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Silver nanotechnology has received tremendous attention in recent years, owing to its wide range of applications in various fields and its intrinsic therapeutic properties. In this review, an attempt is made to critically evaluate the chemical, physical, and biological synthesis of silver nanoparticles (AgNPs) as well as their efficacy in the field of theranostics including microbiology and parasitology. Moreover, an outlook is also provided regarding the performance of AgNPs against different biological systems such as bacteria, fungi, viruses, and parasites (leishmanial and malarial parasites) in curing certain fatal human diseases, with a special focus on cancer. The mechanism of action of AgNPs in different biological systems still remains enigmatic. Here, due to limited available literature, we only focused on AgNPs mechanism in biological systems including human (wound healing and apoptosis), bacteria, and viruses which may open new windows for future research to ensure the versatile application of AgNPs in cosmetics, electronics, and medical fields.
The focus of this review is to provide a comprehensive, well-elaborated, and up-to-date view about what is currently investigated about the antimicrobial and antiparasitic activities and various methods used for the synthesis of AgNPs. Besides, we strive to compile all the most recent investigations about the applications of AgNPs in many fields with a special focus on cancer and viral infection inhibition, and the toxicology of AgNPs. We strongly believe that this review will provide a handy mechanistic framework for the future analysis of AgNPs.
Nowadays, the applications of nanoparticles are tremendously increasing as they possess unique optical, chemical, electrical, electronic, and mechanical properties. These properties are attributed to their large surface area-to-volume ratio, which imparts them unique properties as compared to atoms/molecules as well as the bulk of the same material. Metallic particles, specifically AgNPs, are in focus due to their antimicrobial resistance as metal ions, while antibiotics are losing their effectiveness due to development of resistant strains of microbes. 1 Although the antimicrobial properties of AgNPs are extensively studied, their activities against other types of pathogens such as arthropods and different types of cancer cells have been evaluated only recently. AgNPs as therapeutic agents have achieved remarkable attention in the treatment of cancer, leishmania, malaria, and many other human diseases. However, there still remain many questions that are a matter of discussion for future research.
Currently, different metals including zinc, titanium and copper, 9 magnesium and gold, 10 , 11 and alginate 12 are used as antimicrobial agents, but among these AgNPs have been found to be the most efficient due to their outstanding antimicrobial properties. 13 In particular, nanosilver has been verified to have a great medicinal value attributable to its characteristic antibacterial, 13 , 14 antifungal, 9 antiviral, 15 antiprotozoal, 16 anticatalytic, 17 and antiarthropodal characteristics. 18 In cancer, metastasis is a great challenge to oncologists and clinicians due to the development of resistance to anticancer agents; 19 however, this problem can be overcome by nanoscale materials, especially nanosilver.
Various terminologies are used for silver particles such as colloidal silver, nano-silver, silver nanostructures, and silver nanoparticles (AgNPs). For the sake of convenience, we use the abbreviation AgNPs throughout this review. Nanotechnology is an advanced field dealing with the manufacturing of different kinds of nanomaterials having biomedical applications. 4 Due to a wide range of transmittable diseases caused by different pathogenic bacteria and their enhanced antibiotic resistance, many pharmaceutical companies and researchers are striving for synthesizing novel materials with enhanced antibacterial activity and reduced side effects. Currently, nanoscale materials have achieved considerable attention as novel antimicrobial agents due to their high surface area-to-volume ratio and distinct physical and chemical properties. 5 – 7 The extremely strong broad-spectrum antimicrobial property of AgNPs is the key direction for the improvement of AgNPs-based biomedical products, including bandages, catheters, antiseptic sprayers, textiles, and food storage containers. 8
“Nano” is a Greek word meaning small or dwarf. Nanoparticles can be defined as the particles ranging in size from 1 to 100 nm in either direction but can be considered as ranging up to several hundred nanometers. 1 These are actually aggregates of atoms, ions, or molecules. 1 In other words, “nano” is used to represent one billion of a meter or can be referred to as 10 −9 m. The concept of nanotechnology was first defined by Professor Norio Taniguchi in 1974, and since then, the field of nanotechnology has been receiving immense attention, especially from the early 1980s. 2 , 3
Graphene oxide (GO), an oxidized form of graphene, has been extensively used for various applications since the discovery of graphene in 2004. 207 Recently, GO has been utilized as a platform for growing NPs or attaching pre-synthesized NPs on its surface to produce NP-GO nanocomposites (NCs). Interestingly, NP-GO NCs exhibit enhanced surface enhanced Raman scattering, catalytic, and antibacterial properties compared to bare GO and NP. 208 – 213 Recent studies reported the fabrication of AgNPs-decorated GO as an effective antibacterial agent. 213 – 216
Over the past decade, silk fibroin has been applied in tissue engineering as a degradable surgical suture and scaffold 197 , 198 for its good biocompatibility, controllable biodegradability, and easy fabrication into different forms, such as fibers, films, gels, and three-dimensional scaffolds. 199 Silk fibroin is a good candidate for biomineralization. Previous works have indicated that silk fibroin regulates the morphologies of inorganic nanoparticles during the biomineralization process. 200 , 201 Silk fibroin contains 18 types of amino acid residues, including some polar amino acids such as tyrosine (Tyr). Tyr endows silk fibroin with the electron-donating property. The electron-donating property of the phenolic hydroxyl group of Tyr could directly reduce silver ion to AgNP. 202 Thus, it is possible to synthesize AgNPs through the reduction of Ag + by silk fibroin in situ to prepare the antibacterial silk film. Biopolymer film such as AgNPs silk is limited in its packaging application due to its poor mechanical property. To improve the mechanical property, biopolymer–polymer interaction is developed by blending natural biopolymers with polymers. PVA is a biodegradable, biocompatible, water-soluble, and nontoxic semicrystalline polymer. It offers good thermomechanical property, thermal stability, mechanical strength, and flexibility, as well as good optical and physical properties that are crucial for packaging application. 203 , 204 Moreover, PVA is approved by the US Food and Drug Administration as an indirect food additive for flexible food packaging. 205 , 206 The combination of AgNPs, silk fibroin, and PVA will be promising for active packaging.
Sericin, a globular glue protein, is exclusively produced in the middle silk gland of silkworm when silkworm spins a cocoon for protective and adhesive effects. 195 Silkworm cocoon is usually composed of about 75% fibroin and 25% sericin. However, sericin has been disposed of as a waste during the silk reeling process in the past few thousand years. It is not only a great waste of natural resources but also causes serious environmental pollution. Modern studies propounded that sericin performs a variety of biological activities, such as anticoagulation, antioxidant, antibacterial, and mitogenic effects, on mammalian cells. In regenerative medicines, it is usually mingled with functional polymers to form various scaffolds for biomedical purposes. 195
Cellulose is also one of the most important groups of polysaccharides, and due to its unique properties, cellulose is considered as an excellent template for the nanosilver formation. Both soluble and insoluble cellulose have been employed for the preparation of AgNPs, where alcohol and aldehyde groups performed an important role in the stabilization and reduction of silver ions 191 as presented in . Recently, the green synthesis of AgNPs using hydroxyl propyl cellulose (HPC) has also been reported. HPC plays a dual role (reducer and stabilizer) in the synthesis of AgNPs. 192 , 193 Insoluble cellulose was also investigated for the synthesis of AgNPs. Furthermore, it was indicated that various types of fibers were used in the silver salt solution. Meanwhile, experimental results showed that AgNPs of undetectable size to 160 and 50 nm were deposited on cotton and viscose fibers, respectively. Recently, cotton fabrics were investigated for the synthesis of the AgNPs. Trisodium citrate was used as a reducing agent at 90°C. Experimental results indicated that 20–90 nm AgNPs can be obtained. 194
It was also found that gum ghatti and gum kondagogu can be used as stabilizer and reducing agent for the synthesis of AgNPs. 180 , 181 Using gum ghatti, narrow-sized (4.8–6.4 nm) AgNPs were produced, whereas gum kondagogu produced 2–9 nm AgNPs. 181 Moreover, AgNPs of undetectable size to 25 nm (spherical) were also obtained from alkali-soluble xanthan and acacia. 182 , 183 Schizophyllan 184 and hyaluronic acid (HA) 185 were used as reducer and stabilizing agent for the synthesis of AgNPs. HA was analyzed chemically and thermally, and the results showed that 5–30 nm AgNPs can be obtained. 185 Similarly, carboxymethyl chitosan and N-phthaloyl chitosan were also used in the preparation of nanosilver. 186 – 188 In a recent report, it was investigated that under acidic medium, silver chitosan film was formed due to the mixing of both silver salts and chitosan. 189 Also, acidic medium and chitosan were used as chelating agents for AgNPs. 190
The starch solution (reducing/capping agent) and AgNO 3 (salt) have been used for the synthesis of AgNPs, and using these agents, stable AgNPs sized 10–34 nm were formed. These nanoparticles were stable in the aqueous solution at 25°C for around 3 months. 172 Similarly, small-sized AgNPs (5–20 and ≤10 nm) can be prepared using starch (stabilizer and capping agent) and NaOH solution having glucose (reducing agent). 173 , 174 Small-sized (1–21 nm) and spherical-shaped AgNPs have been synthesized using carboxymethyl starch in aqueous solution with a stability of more than 3 months at 25°C. 175 The alkaline solutions can also be used for solubilization of spherical nanoparticles in starch. 176 Recent studies revealed that ester of alginic acid (sodium and calcium alginate) can be used for the preparation of AgNPs. 177 , 178 Some studies also reported that the spherical-shaped and small-sized (1–4 nm) AgNPs can be obtained in 1 min from sodium alginate using water as solvent at 70°C. 179
Polysaccharides have been widely used for biomedical applications, as they are biocompatible and biodegradable. Polysaccharides are considered as excellent templates for the preparation of nanosilvers. Polysaccharides play a dual role, that is, reductants and/or capping agents, in the synthesis of AgNPs. For more than a decade, gentle heating of starch (capping agent) and β-d-glucose (reducing agent) has resulted in the formation of AgNPs. 171
Algae have been recently studied for the synthesis of AgNPs. Venkatpurwar and Pokharkar reported the formation of AgNPs from aquatic red algae using sulfated polysaccharides. These AgNPs were highly constant at broad pH range (2–10) and showed effective antibacterial activity against Gram-negative than Gram-positive bacteria. 167 El-Rafie et al extracted water-soluble polysaccharides from aquatic microalgae. These polysaccharides were used as both reducing and stabilizing agents for AgNPs formation. The colloidal solutions imparted antimicrobial activity when tested on cotton fabrics. 168 More recently, Salari et al were able to synthesize AgNPs from macroalgae Spirogyra varians through bio-reduction of silver ions. These AgNPs functioned as efficient bactericidal mediators in response to many pathogenic bacteria. 169 Some other algal species, namely Tetraselmis gracilis, Chaetoceros calcitrans, Isochrysis galbana, and Chlorella salina, can be successfully used for the AgNPs biosynthesis. 170
The spherical nanosilver can also be synthesized using Coriolus versicolor, but the reduction of AgNPs is time consuming (ie, 72 h; however, the duration could be reduced to 1 h by tailoring the reaction conditions using alkaline media at pH 10). The alkaline media play a vital role in the bio-reduction of silver ions, water hydrolysis, and interaction with protein functionalities. Furthermore, the S–H group from the protein plays an excellent role in the bio-reduction, whereas glucose molecule also plays a significant role in the reduction of AgNPs. 165 Aspergillus flavus can also be used to obtain stable nanosilver with more than 3 months of stability in aqueous solution. Meanwhile, the stabilizing agents released by fungal species ensure prevention of aggregation. 166
Balaji et al used an extracellular solution of Cladosporium cladosporiodes for the reduction of AgNO 3 to form spherical-shaped AgNPs of 10–100 nm size. They further reported that C. cladosporiodes released some organic materials, including polysaccharides, organic acids, and proteins, which were responsible for the formation of spherical crystalline AgNPs. 126 Penicillium spp. were also used for the production of AgNPs. 163 Soil-isolated Penicillium spp. J3 which has the ability to produce silver nanoparticles was used for the synthesis, and the AgNPs formation took place on the surface of the cells in which proteins acted as stabilizing agents. 164
Recent studies showed that AgNPs of size 5–25 and 5–50 nm could be extracellularly synthesized using Aspergillus fumigatus and Fusarium oxysporum, respectively. 161 , 162 The authors further reported that most of the nanoparticles were spherical in shape; however, rare triangular-shaped nanoparticles were also noticed. 161
Green and/or biogenic synthesis of any type of nanoparticles involves natural processes occurring in microorganisms like fungi, bacteria, and plants, as shown in . These organisms generate biocompatible nanostructures having excellent therapeutic potential. 131 Fungi-based synthesis of AgNPs is also eco-friendly and of low cost. In a recent study, two fungal strains, namely Penicillium expansum HA2N and Aspergillus terreus HA1N, were reported for the synthesis of AgNPs. The transmission electron microscopy result showed that 14–25 nm AgNPs were obtained from P. expansum, while 10–18 nm AgNPs were obtained from A. terreus. The efficacy of these AgNPs was further examined against different fungal species which demonstrated their strong antifungal potential. 62
Like other methods, metal precursors or silver salts are also used in the preparation of silver nanostructure from bacterial cultures. The production of AgNPs using sulfide (Ag 2 S) and oxide (Ag 2 O) of silver has also been reported by various studies. 31 , 156 In a recent report, the culture supernatant of bacterium Bacillus licheniformis was used to produce 40 and 50 nm AgNPs, respectively. 157 , 158 AgNPs of 1–6 nm size has also been produced using visible light emission from the supernatants of Klebsiella pneumoniae. 159 Furthermore, it was also found that Lactobacillus strains can be used for the production of AgNPs. 155 , 160 Recently, the bacterial strains of Aeromonas spp. SH10 and Corynebacterium spp. SH09 were screened for the biosynthesis of AgNPs. The authors concluded from their results that the bio-reduction of [Ag(NH 3 ) 2 ] + resulted in the production of monodispersed and stable AgNPs. 153
Klaus et al were the first to explore the ability of the bacterium Pseudomonas stutzeri AG259 to synthesize AgNPs. The bacteria exhibited a remarkable property of surviving in an extreme silver-rich environment, which might be the possible explanation for the accumulation of nanosilver. 150 Nanosilver particles have been synthesized using both Gram-positive and Gram-negative bacteria including the silver-resistant bacteria to form AgNPs. 151 Some bacteria have the ability to produce extracellular AgNPs, while others can synthesize intracellular AgNPs. Interestingly, some bacteria including Calothrix pulvinata, Anabaena flos-aquae, 152 Vibrio alginolyticus, 33 Aeromonas spp. SH10, 153 Plectonema boryanum UTEX 485, 154 and Lactobacillus spp. 155 have the ability to produce both extra- and intracellular AgNPs.
The biosynthesis of AgNPs was reported for the first time using identified antimicrobial molecules (gallic acid + apocynin) and (gallic acid + apocynin + quercetin) from the medicinal plant Pelargonium endlicherianum Fenzl., and these AgNPs had dramatically enhanced antimicrobial activity. 149
A simple, environmental-friendly, and cost-effective method has been developed to synthesize AgNPs using tea leaf extract. The synthesized AgNPs showed a good stability in terms of time-dependent release of silver ions. Due to the larger size and less silver ion release, the synthesized NPs showed low antibacterial activity against E. coli. 148
Babu and Prabu described the AgNP synthesis using a leaf extract of C. camphora, while the reduction was considered to be due to presence of the phenolics, terpenoids, polysaccharides, and flavonoids in the extract. 147
Chandran et al 140 and Li et al 141 reported the synthesis of AgNPs from the leaf extracts of Aloe vera and Capsicum annum plants, respectively. The rapid synthesis of AgNPs using the fruit extract of Carica papaya was demonstrated, and it was found that the synthesized nanoparticles were highly toxic against different multidrug-resistant (MDR) human pathogens. 142 Begum et al 143 were able to synthesize stable AgNPs of various shapes using black tea leaf extract. Extracellular synthesis of AgNPs was also carried out using leaf extract of Pine, Persimmon, Ginkgo, Magnolia, and Platanus plants. 144 In addition, AgNPs were successfully synthesized using the latex and seed extract of Jatropha curcas. 145 The compatibility of the bark and powder extracts of Curcuma longa was also checked towards the formation of AgNPs, and it was reported that bark extract could produce a higher amount of AgNPs compared to the powder extract. 146
The cubic- and hexagonal-shaped AgNPs of 31–40 nm size were obtained using the bark extract of Cinnamon zeylanicum. 137 Spherically shaped nanosilver sized 1–10 nm was synthesized from geraniol (C 10 H 18 O) compound isolated from two important medicinal plants, namely Pelargonium graveolens and Azadirachta indica. These AgNPs ablated fibrosarcoma Wehi 164 cancer cells. 86 In another study, ten different Cassia medicinal plant species were screened for the biosynthesis of AgNPs. It was also found that the leaves of P. graveolens and Cinnamomum camphora contained terpenoids which were responsible for the biosynthesis of AgNPs. 130 , 138 Among them, only the aqueous leaf extract of Cassia roxburghii supported the synthesis of stable AgNPs (35 nm size). These nanoparticles were further tested against human and plant pathogenic fungi, and they exhibited excellent result as compared to tested standard drugs. 139
In a recent study, the leaf extract of Ocimum sanctum was found to reduce Ag + ions into crystalline AgNPs having a size of 4–30 nm in 8 min. However, due to the presence of ascorbic acid in the plant leaves, the silver ions were readily reduced to metallic silver. The authors related the stability of the particles to the presence of proteins which played an important role as capping agents. The resulted AgNPs were effective against Escherichia coli and S. aureus. 136
Plant-based production is one of the most cost-effective and valuable alternative large-scale method for synthesizing AgNPs. 132 Researchers have put attempts and focused to synthesize AgNPs of varying size and shape using different plant extracts with a broad range of antimicrobial, anticancer, antiviral, and anticatalytic activities as shown in . Euphorbia hirta leaf extract was used for the synthesis of AgNPs resulting in the production of spherical nanoparticles sized 40–50 nm. These AgNPs showed strong activity against Bacillus cereus and Staphylococcus aureus bacterial strains. 133 Krishnaraj et al and Veerasamy et al were able to synthesize AgNPs of size 20–30 and 35 nm, respectively, using leaf extracts of the medicinal plants Acalypha indica and Garcinia mangostana. 134 , 135
The bio-based or green synthesis of AgNPs has great advantages over chemical and physical methods. Biologically synthesized AgNPs are eco-friendly, as no toxic reductants or stabilizing agents are used during the synthesis of nanoparticles. In biological systems, the health hazardous reducing and stabilizing agents can be substituted by essential biomolecules such as proteins 121 and carbohydrates, 122 which are locally produced by microbes including bacteria, 23 , 123 – 125 fungi 24 , 62 , 126 , 127 and yeast, 127 – 129 plants, 25 , 127 , 130 , 131 and lower organisms like algae. 127 , 130 , 131 The different reducing, capping, or stabilizing agents and silver salts or metal precursors which are used during biological method are presented in . Herein, we summarize some important biogenic synthesis or biological systems such as plants, bacteria, fungi, and algae using proteins and polysaccharides as reducing and stabilizing agents for the synthesis of AgNPs.
The sonoelectrochemistry technique utilizes the ultrasonic power primarily to manipulate the material mechanically. The pulsed sonoelectrochemical synthetic method involves alternating sonic and electric pulses. Electrolyte composition plays a crucial role in shape formation. 120 It was reported that silver nanospheres could be prepared by sonoelectrochemical reduction using a complexing agent, nitrilotriacetate, to avoid aggregation. 120
Previous studies demonstrated that UV light can assist in the reduction of silver ions to immobilize AgNPs on the surface of the polymer. Synthesis approach was applied to immobilize AgNPs in situ on the surface of sericin gel with the assistance of UV light. Scanning electron microscopy (SEM), X-ray diffractometry, Fourier-transform infrared spectroscopy, and differential scanning calorimetry were applied to characterize the surface tomography and structure of the AgNPs-modified sericin materials. Sericin gel was cut into small sheets and then soaked into 50 mM AgNO 3 solution. At the same time, sericin gel sheets were irradiated with a 365 nm UV light lamp (24 W) for 10, 30, and 60 min to make AgNPs immobilize on the surface of sericin gel, respectively. The collected AgNPs-modified sericin gel sheets were dried at room temperature, and then their surface tomography, structure, and antimicrobial activity were studied. 119
A simple and effective method, ultraviolet (UV)-initiated photoreduction, has been reported for the synthesis of AgNPs in the presence of citrate, PVP, poly (acrylic acid), and collagen. For instance, Huang and Yang produced AgNPs via photoreduction of AgNO 3 in layered inorganic laponite clay suspension which served as a stabilizing agent for the prevention of NPs aggregation. The properties of produced NPs were studied as a function of UV irradiation time. Bimodal size distribution and relatively large AgNPs were obtained using UV irradiation for 3 h. Further irradiation disintegrated the AgNPs into smaller-sized particles with a single distribution mode until a relatively stable size and size distribution were obtained. 117 Silver NPs (nanosphere, nanowire, and dendrite) have been prepared by UV irradiation photoreduction technique at room temperature using poly (vinyl alcohol) (PVA) (as protecting and stabilizing agent). The concentration of both PVA and AgNO 3 played a significant role in the growth of the nanorods and dendrites. 118
Some studies documented that AgNPs were formed when bulk materials in solution were subjected to laser ablation technique. 22 , 113 – 115 Meanwhile, it was also found that silver nanospheroids sized 20–50 nm can be obtained by the same technique in pure water with femtosecond laser pulses at 800 nm. 71 Laser ablation method has an advantage over other techniques because there is no need to add any reagent to solutions. Thus, laser ablation technique is useful for the production of uncontaminated and pure metal colloids. 116
Tsuji et al used the small ceramic heater and laser ablation method, respectively, to synthesize AgNPs. 116 Later on, investigators successfully synthesized colloidal AgNPs in a metal solution with no chemical reagent added. Furthermore, using arc discharge method, Tien et al produced AgNPs having 20–30 nm size in pure water without the addition of any stabilizers or surfactants. 103
The most important physical techniques frequently used for the preparation of AgNPs include evaporation/vapor condensation, 22 , 102 , 108 arc discharge, 109 energy ball milling, 110 and direct current magnetron sputtering method. 23 Compared to chemical methods, physical methods are generally less time consuming and do not involve any type of hazardous chemicals. 110 However, high energy consumption and requirement of long time for thermal stability are still the bottlenecks of these methods. 22 , 111 , 112
Irradiation is another method to prepare AgNPs. Abid et al concluded from their study that AgNPs of definite shape and size can be produced using laser irradiation of surfactant and an aqueous solution of silver salt. 106 Sudeep and Kamat successfully induced the synthesis of AgNPs in ethanol/toluene organic solution. 107 However, more investigations are needed to further address the possible in vitro and in vivo potential toxicities that can be the outcomes of the chemical method used for synthesizing AgNPs.
Similar to chemical reduction method, the silver nanostructure can be synthesized by an electrochemical method. Using this approach, small-sized (10–20 nm) AgNPs with spherical shape can be produced. 78 Furthermore, using crystals of zeolite, monodisperse silver nanospheroids of size 1–18 nm have been formed by electrochemical reduction. 105 However, using organic and aqueous interface, polyphenylpyrrole-coated silver nanospheroids of size 3–20 nm can be obtained by electrochemical method. 77
In their recent study, Zhang et al reported that colloidal silver could be synthesized through the chemical reaction of polymethylene bisacrylamide aminoethyl piperazine with terminal dimethylamine groups (HPAMAM-N (CH 3 ) 2 ). Later on, it was documented that these groups have strong reducing and stabilizing potential. 104 In another case study, it was demonstrated that polyol process and modified injection technique could produce spherical, highly mono-dispersed AgNPs of controllable size. The reaction temperature and rate of injection were important factors in this method to obtain uniform AgNPs of reduced sized. AgNPs with 17±2 nm diameter were obtained at 100°C and 2.5 mL/s injection rate. 73
The commonly reported stabilizing/capping agents include surfactants and polymeric compounds such as polyvinyl pyrrolidone (PVP), PEG, poly(N-isopropylacrylamide), poly (methyl methacrylate), poly (methacrylic acid), and collagen. 101 , 102 Among these stabilizers, the alcohols, thiols, amines, acidic functional groups, and surfactants protect the nanoparticles from sedimentation as well as protect them from losing their surface properties. Silver nitrate (AgNO 3 ) is the most significant silver salt frequently used for the preparation of AgNPs, and as compared to other salts, it is chemically stable, easily available, and cost-effective. 103 A detailed summary of reducing, capping, or stabilizing agents and silver salts or metal precursors used in biological, chemical, and physical methods is provided in .
AgNPs can be synthesized by chemical reduction, 92 electrochemical technique, 20 irradiation-assisted chemical method, 93 and pyrolysis; 21 of these, chemical reduction has been the most common route to synthesize nanosilver. Three main components, namely organic and inorganic reducing agents, capping agents or stabilizers, and metal precursors or silver salts, are used in this method ( ). Hydrogen gas, 94 borohydride, 80 , 94 , 95 citrate, 96 ascorbic acid, 97 hydrazine compounds, polyol process, Tollens’ reagent, N,N-dimethylformamide, and poly (ethylene glycol) (PEG)-block polymers are the reducing agents most frequently used in this method. These reductants bring about a reduction of silver ions (Ag + ) to metallic silver (Ag 0 ) followed by agglomeration into oligomeric clusters in aqueous and nonaqueous solutions. Finally, these clusters form metallic colloidal nanosilver. 98 – 100 Borohydride has been extensively used for reduction process because of its strong and rapid reductant properties as well as its ability to act as a stabilizer to evade aggregation of AgNPs throughout decaying. 94
AgNPs can be synthesized by various methods ( ) including chemical synthesis, 8 , 20 – 22 physical techniques, 8 , 22 , 23 and green or biological methods. 24 – 26 Some important examples for biological, physical, and chemical synthesis of AgNPs are mentioned in .
Antimicrobial activities of AgNPs as presented in and have been known for many centuries, but their assessment on a scientific basis has only been realized in recent years. Sondi and Salopek-Sondi for the first time depicted AgNPs performance against E. coli, to propose a possible enlightenment of the observed action of AgNPs on bacteria. The authors revealed that the appearance of “pits” in bacterial cell wall and accumulation of AgNPs in the cellular membrane resulted in an enhanced permeability of cell wall and eventually induced bactericidal activity.218
Open in a separate windowDevi and Joshi evaluated 53 strains of various fungi for the mycosynthesis of AgNPs and showed considerable effectiveness of AgNPs against Streptococcus pyogenes, Salmonella enterica, S. aureus, and Enterococcus faecalis.219 Moreover, the mycosynthesized nanoparticles also exhibited potential antibacterial activity and synergistic effect with erythromycin, chloramphenicol, methicillin, and ciprofloxacin against Enterobacter aerogenes and K. pneumoniae66 and with antibiotics ampicillin, tetracycline, gentamycin, and streptomycin against E. coli, S. aureus, and Pseudomonas aeruginosa.220 The antibacterial activity of AgNPs strongly depends on the size of the silver particles as reported in previous reports. AgNPs with a smaller size have high activity due to a relative increase in contact surface.221
Shameli et al reported size-based bactericidal potential of various AgNPs prepared in PEG against S. aureus and Salmonella typhimurium bacteria using disc diffusion method. AgNPs were found to be very effective and cause momentous inhibition of both strains. They summarized that the bactericidal potential of AgNPs in PEG can be tuned by controlling the size of nanoparticles, since smaller particles have a relatively greater contact surface area than larger particles. The factors that are influencing the activity of AgNPs (size, shape, concentration, UV radiation, and combination with different antibiotics) should be taken into account during the preparation processes and medicinal applications of AgNPs.222 Similarly, investigations by Raheman et al and Gade et al had already demonstrated the biocidal potential of AgNPs, respectively.67,223 Silver bionanocomposite films having a size less than 20 nm were tested against E. coli, P. aeruginosa, S. aureus, and Micrococcus luteus. These silver composites exhibited satisfactory antibacterial properties.224
In recent studies, spherical-shaped 20, 18, and 15 nm AgNPs were prepared. The experimental result showed that all AgNPs were active against different strains of bacteria.13,17 In another study, AgNPs having a spherical shape and ranging in size from 5 to 30 nm and crude latex aqueous extract were tested against different bacterial pathogens such as Enterococci spp., B. cereus, Shigella spp., P. aeruginosa, S. aureus, K. pneumoniae, and E. coli. These biosynthesized AgNPs were found to have the capability of enhancing the antimicrobial activity compared to crude latex aqueous extract.225 The nanoparticles assumed spherical geometry and were often aggregated into small particles with quite a uniform size of 12.50–41.90 nm. These AgNPs showed exceptional antibacterial property against different strains of bacteria. Afterwards, they were found to be more effective against E. coli and K. pneumoniae than against E. faecalis and S. mutans. This differential activity may possibly be due to the difference in bacterial cell wall structure.226
Recently, AgNPs with an average uniform size of 5 nm were tested against bacteria. Results indicated that the efficiency of antibiotics was improved in the presence of AgNPs against test strains. The activity of AgNPs was more pronounced with ampicillin against the Gram-negative bacteria Shigella flexneri and P. aeruginosa, and vancomycin against the Gram-positive bacteria Streptococcus pneumoniae and S. aureus. More interestingly, these antibiotics exhibited higher antimicrobial efficiency in association with AgNPs. These results suggested that AgNPs could be used as an adjuvant for curing various infectious diseases caused by bacteria.4 AgNPs which were synthesized by the green method and their antibacterial properties were studied using diffusion method. The concentration of AgNPs was varied as 25, 50, 75, and 100 μg/mL. The highest efficiency of AgNPs was found against S. aureus (23 mm) and E. coli (28 mm). The moderate activity was obtained against Salmonella typhi (18 mm) followed by M. luteus (15 mm) and P. aeruginosa (13 mm).19
AgNPs, having a size of 26 nm, have been reported to be efficient against E. faecalis CCM 4224, S. aureus CCM 3953, E. coli CCM 3954, and P. aeruginosa CCM 3955. The modified antibacterial activity of silver NPs was considerably improved as confirmed by minimum inhibitory concentration (MIC) values ranging from 6.75 down to 0.84 μg/mL.227 In another study, the growth rates of bacteria were studied under varying AgNPs concentrations, incubation temperatures, times, and pH. E. coli and S. aureus were shown to be substantially inhibited by AgNPs, and the antibacterial activity of AgNPs did not change with pH or temperature.228
AgNPs in montmorillonite were prepared, and their antibacterial activities against S. aureus and methicillin-resistant S. aureus (Gram-positive bacteria) and E. coli, E. coli O157:H7, and K. pneumoniae (Gram-negative bacteria) were tested by the disc diffusion method using Mueller–Hinton agar. The smaller AgNPs exhibited significantly higher antibacterial activity.229 More recently, cream formulations of AgNPs and AgNO3 were prepared, and their antibacterial activity was evaluated on human pathogens (S. aureus, Proteus vulgaris, E. coli, P. aeruginosa, and Candida albicans) and a plant pathogen (Agrobacterium tumefaciens). The antimicrobial studies concluded that AgNPs have 200 times more inhibitory effect compared to AgNO3. The AgNPs act by damaging the cell membrane of E. coli, which was confirmed by SEM study.230
The antibacterial activity of AgNPs was tested against nine human diseases-causing Gram-negative bacteria and one Gram-positive bacteria. AgNPs extracts had the capability to enhance antibacterial activity against all tested strains compared to the extracts alone. AgNPs were more bactericidal in liquid than in solid medium, probably due to better contact with bacterial cells in a liquid state. Maximum zone of inhibition was 19 mm for nanoparticles of leaves on P. aeruginosa (ATCC278223) and 18 mm for latex nanoparticles on S. flexneri (ATCC12022). The minimum zone of inhibition was 7 mm for both nanoparticles of leaves and latex on S. typhi (ATCC19430) and S. typhimurium (ATCC14028), respectively.231
The leaf extract of Lantana camara was used for the biosynthesis of AgNPs. These nanoparticles were evaluated for catalytic and antibacterial activities. The biosynthesized nanosilver had excellent potential against the tested strains including E. coli, Pseudomonas spp., Bacillus spp., and Staphylococcus spp. Moreover, these AgNPs also showed higher catalytic activity in the reduction of methylene blue observed using UV–vis spectrophotometer.232 Spherical nanosilver sized 10–15 nm was synthesized from fresh spinach leaves. These nanoparticles had strong bactericidal potential and good catalytic property toward methyl red and methylene blue.233
A recent study on the effect of AgNPs (13.4 nm) against E. coli and S. aureus found their MIC values to be below 6.6 nM and above 33 nM, respectively.234 Another study was conducted against the bacterium E. coli. The results showed that AgNPs (16 nm) had the ability to inhibit E. coli colony-forming unit at a concentration of 60 μg/mL.235 Furthermore, the activity of some important dendrimer (poly-amidoamine) Ag-composites has also been reported against E. coli, S. aureus, P. aeruginosa, Klebsiella mobilis, and Bacillus subtilis.104
The antimicrobial property of AgNPs is most exploited in the medical field, though their anti-inflammatory nature is also considered immensely useful. Initial studies have suggested that the acceleration of wound healing in the presence of nanoparticles is due to the reduction of local matrix metalloproteinase activity and the increase in neutrophil apoptosis within the wound.
Recent evidence suggests that nanosilver has a potent anti-inflammatory effect236–238 and accelerates wound healing.239,240 Silver has long been known to possess antibacterial activity and has been used throughout history, from Hippocrates’ early treatment of ulcers to C.S.F. Crede’s treatment of gonococcal infections in newborns. Silver is still used clinically, and nanosilver is emerging as a valuable tool in the therapeutic armory ( ). Silver sulfadiazine is the gold standard for the topical treatment of burn patients.241 The resurgent interest in silver and nanosilver has been motivated by the emergence of rampant antibiotic-resistant bacteria and the increasing prevalence of hospital-acquired bacterial infections. The use of silver has been severely limited by the toxicity of silver ions to humans; however, nanotechnology has facilitated the production of smaller silver particles with increasingly large surface area-to-volume ratios, greater efficacy against bacteria,242,243 and most importantly, lower toxicity to humans.244
Nanocrystalline silver wound dressings have been commercially available for over a decade (eg, Acticoat™) and are in current clinical use for the treatment of various wounds, including burns,240,245,246 toxic epidermal necrolysis,247 Stevens–Johnson syndrome,248 chronic ulcers,237 and pemphigus.248 Typical dressings consist of two layers of polyethylene mesh forming a sandwich around a layer of polyester gauze. Typical nanocrystalline coatings are 900 nm thick with a crystallite size of 10–15 nm236 and are applied to the polyethylene layer.
In 2008, Kim et al demonstrated the potential of AgNPs against 44 strains of six fungal species, namely Candida tropicalis, C. albicans, Candida glabrata, Candida krusei, Candida parapsilosis, and Trichophyton mentagrophytes. The AgNPs were found active against various strains of T. mentagrophytes and Candida spp.249 Similarly, Velluti et al found that nanosilver complexes [Ag2(SMX)2] showed good activity against 10 fungal strains, namely C. tropicalis (C 131), C. albicans (ATCC 10231), Cryptococcus neoformans (ATCC 32264), Saccharomyces cerevisiae (ATCC 9763), A. fumigatus (ATCC 26934), A. flavus (ATCC 9170), Aspergillus niger (ATCC 9029), dermatophytes including Trichophyton rubrum (C 113), T. mentagrophytes (ATCC 9972), and Microsporum gypseum (C 115).250
Gajbhiye et al reported the efficiency of biogenic AgNPs against Pleospora herbarum, Phoma glomerata, Fusarium semitectum, Trichoderma spp., and C. albicans. Furthermore, they also reported the synergistic effects of AgNPs in association with fluconazole.251 In 2009, Jo et al demonstrated the antifungal potential of silver ions and nanoparticles against two plant pathogenic fungi, Magnaporthe grisea and Bipolaris sorokiniana. The fungicidal potential of AgNPs in combination with various heterocyclic compounds like phthalazine, thiazolidine, hydrazide, pyrazolo, tetrazolo, and pyridazine derivatives was studied against C. albicans and A. flavus, and the AgNPs were found to have significant fungicidal activity against tested organisms.252
Recently, six fungal species, namely Penicillium brevicompactum, A. fumigatus, Mortierella alpina, C. cladosporoides, Chaetomium globosum, and Stachybotrys chartarum, were selected for the study of the antifungal activity of AgNPs. The growth rates of all tested fungal species, except Mortierella spp., were affected by the addition of AgNPs, which caused the limitation of Chaetomium and Stachybotrys on gypsum products. Each fungus showed a distinct response to applied AgNPs depending upon the concentration and the rate of Ag ions released into the environment.253
In 2010, Jaidev and Narasimha demonstrated the antifungal (A. niger) and antibacterial (Staphylococcus spp., E. coli, Bacillus spp.) activities of AgNPs. They reported that nanosilver has excellent inhibitory activity against A. niger confirming the maximum activity as compared to Bacillus spp. (0.8 cm), Staphylococcus spp. (0.9 cm), and E. coli (0.8 cm).69 Meanwhile, Nasrollahi et al studied the fungicidal potential of AgNPs against S. cerevisiae and C. albicans. Their results were productive confirming the excellent potential of AgNPs as compared to standard antifungal agents (viz. fluconazole and amphotericin B).254 Savithramma et al prepared AgNPs using a different extract of medicinal plants, Shorea tumbuggaia, Boswellia ovalifoliolata, and Svensonia hyderobadensis, to evaluate their antifungal activity against A. niger, Curvularia spp., A. flavus, Fusarium spp., and Rhizopus spp. The results confirmed that all biogenic AgNPs showed considerable antifungal activity against various fungal spp. The AgNPs synthesized with S. hyderobadensis exhibited higher activity as compared to AgNPs synthesized using the other two plants.255
Kaur et al reported the fungicidal potential of silver and chitosan nanoparticles against A. flavus, Rhizoctonia solani, and Alternaria alternata from chickpea seeds.256 In 2012, Arjun and Bholay also demonstrated the momentous efficiency of AgNPs against T. rubrum, C. albicans, and A. fumigatus.257 Xu et al also tested nanosilver and natamycin against 216 strains of fungi from patients suffering from severe keratitis. These included 82 isolates of Aspergillus, 112 isolates of Fusarium, and 10 isolates of Alternaria. Results demonstrated that AgNPs had higher activity as compared to natamycin.258 Similarly, Dar et al studied the biocidal potential of AgNPs synthesized from Cryphonectria spp. against S. typhi, E. coli, S. aureus, and C. albicans, concluding that AgNPs can be used as potential antifungal agents.64
More recently, the antifungal activity of mycosynthesized AgNPs was tested for the first time against plant pathogenic fungi. AgNPs displayed good antifungal activity against Colletotrichum spp. (12.63 mm) followed by R. solani (12.03 mm) and Cochliobolus lunata (11.23 mm) at 1 mg/mL concentration. The nanoparticles were less effective against Fusarium spp. (9.37 mm).259 In another study, AgNO3 was tested against three fungi namely Trichoderma spp. (ATCC 18648), Mucor spp. (ATCC 48559), and A. niger (ATCC 6275), and it was found to exhibit good antifungal activity.260
The antifungal activity of AgNPs against C. tropicalis and C. albicans was also investigated. Stable nanoparticles of size 12.5±4.9 nm (mean ± SD) were obtained, which presented high activity against Candida spp.261 The spherical and polydispersed AgNPs, ranging in size from 4 to 36 nm and 8 to 60 nm, respectively, were applied against superficial mycoses caused by T. rubrum, Malassezia furfur, C. albicans, and C. tropicalis. The AgNPs exhibited highest antifungal activity against T. rubrum and the least against M. furfur and C. albicans as compared to others.262
C. glabrata and C. krusei were exposed to spherical nanoparticles (19 nm) with positive surface charge. The MIC50 values were 0.1–l g mL−1 AgNPs, and minimum fungicidal concentration (MFC) values were 0.25 and 0.5 g mL−1 for C. glabrata and C. krusei, respectively.263 Meanwhile, another research confirmed that concentrations of AgNPs between 10 and 25 μM reduced the growth rates of the tested fungus and bacteria and showed the bactericidal/fungicidal activity by delaying the exponential and stationary phases. However, complete inhibition of the growth of C. albicans MTCC183 was found at a concentration of 10 μM AgNPs.264
A more recent report showed that AgNPs (spherical, 1–40 nm) had excellent antifungal activity against R. solani cultures by inhibiting 83% of the mycelium growth at 25 μg/mL concentration.265 In another study, several essential oils were tested for their antifungal activity. The oil isolated from the bark of Cinnamomum cassia had the highest activity against MIC and MFC values for all tested strains in the range of 0.0006%–0.0097% (v/v) and 0.0012%–0.019% (v/v), respectively.
Further studies were carried out about the antifungal activity of AgNPs against some Candida spp. The fungicidal efficacy of AgNPs functionalized with PVP was established. The PVP-functionalized silver particles demonstrated no damage to fungi until the exposure time was 24 h. After 24 h, no viability of fungal cells was observed. The work revealed that Ag particles aggregate outside the fungal cells, releasing free silver ions and thus inducing cell necrosis through the reduction process.266 Naz et al synthesized silver particles capped with 5-amino-β-resocyclic acid hydrochloride dehydrate (AR). They analyzed their nanostructures before and after conjugation to silver metal for in vitro antifungal, antibacterial, antioxidant, and enzyme inhibitory properties. The results indicated that the fungicidal activity of Ag, AR, and Ag AR were not momentous as compared to the dithane-M45 (standard fungicide).267
AgNPs have been popular for their antibacterial and antifungal activities. However, recent studies have exploited AgNO3 potential in neoplastic maladies. Recently, eco-friendly AgNPs were synthesized from the leaf extracts of Vitex negundo268 and Sesbania grandiflora, and their efficacy was tested against human colon cancer cell lines HCT15 and MCF-7, respectively. The results demonstrated that AgNPs obtained from V. negundo showed antiproliferative effects on cancer cell line, reduced DNA synthesis, and induced apoptosis.268 Similarly, nanosilver obtained from S. grandiflora also caused cytotoxicity, oxidative stress, and apoptosis in tumor cells.269 Moreover, green-synthesized AgNPs from the leaves extract of Podophyllum hexandrum and Suaefa monoica were examined and found to show cytotoxic activity and apoptotic effect, respectively.270,271
Piao et al demonstrated that OH radicals released by the AgNPs attacked cellular molecules including DNA, proteins, and lipids to induce oxidative damages.272 In another report, it was shown that AgNPs exhibited toxicity due to some factors such as dose, size of particles, and time. In the case of MCF-7 cell culture, the toxicity was due to the dose of AgNPs. AgNPs also caused cellular damage in Human Epidermoid Larynx (Hep-2) cell line through reactive oxygen species (ROS) formation.273 Lima et al greenly synthesized nanosilver and evaluated its genotoxicity and cytotoxicity.63 Also, Durán et al studied the potential of biosynthesized AgNPs. These nanosilver particles interacted with DNA, proteins, and cellular organelles via ROS, and induced necrosis and apoptosis in the tumor cells.274
New nanocrystalline silver with a structural size of 8 nm customized with TAT cell penetrating peptide (AgNP-TAT) exhibited higher antitumor property in both nonresistant and MDR cells without any discrimination. The AgNP-TAT displayed outstanding efficacy in killing tumor cells, that is, up to 24-fold higher than pristine AgNO3 without TAT alteration. Moreover, the AgNP-TAT also displayed considerable reduction in adverse toxic effects, in vivo.275
Dimocarpus longan Lour. peel aqueous extract (acts as reducing and stabilizing agent) was evaluated for the synthesis and anticancer and antibacterial effects of AgNPs. The antibacterial activities of AgNPs were evaluated using dilution method, whereas their efficacy against human prostate cancer (PC-3) cells was in vitro evaluated via blue assay and Western blot by the expression of phosphorylated stat 3, caspase-3, bcl-2, and survivin. These nanoparticles had the face-centered cubic structure (size 9–32 nm) and exhibited great bactericidal potential against both Gram-positive and Gram-negative strains of bacteria.276
In another study, Malus domestica and Origanim vulgare extracts were used for the synthesis of nanosilver. The M. domestica extract-biosynthesized silver had considerable effects on MCF-7 breast cancer cells, whereas silver synthesized from O. vulgare aqueous extracts showed dose-dependent response against human lung cancer A549 cell line.277,278
In a recent study, AgNPs were obtained from the stem bark extract of Moringa olifera. These biosynthesized AgNPs were tested for anticancer properties. The flow cytometry results showed apoptosis induced through ROS generation in HeLa cells.279 The rhamnolipids were isolated from P. aeruginosa strain JS-11 and used for the biosynthesis of Rh-AgNPs. These nanosilver particles were tested against MCF-7 human cells.280 Furthermore, caffeic acid-mediated spherical nanosilver particles of 6.67±0.35 nm size were used against cancer cells. The results showed that AgNPs efficiently inhibited the growth of HepG2 cells via apoptosis induction.281
Recently, spherical-shaped (6.2±0.2 nm) silver-(protein-lipid) nanoparticles (Ag-LP-NPs) were obtained using the seed extract of Sterculia foetida. These eco-friendly Ag-LP-NPs showed antiproliferative activity against HeLa cancer cell lines and also showed potential toxicity in a dose-dependent manner.282 More recently, biogenic AgNPs were obtained from the flower extract of Plumeria alba (frangipani) known as frangipani AgNPs (FS NPs). These FS NPs had a cytotoxic effect on COLO 205 which was determined by MTT assay, and after 24 and 48 h of incubation, the IC50 concentration was found at 4 and 5.5 μg/mL, respectively. Furthermore, the FS NPs cytotoxic affect on COLO 205 cells was associated with the loss of membrane integrity and chromatin condensation that have a great role in the induction of apoptosis as evidenced by acridine orange/ethidium bromide staining.283
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Silver nanotechnology has received tremendous attention in recent years, owing to its wide range of applications in various fields and its intrinsic therapeutic properties. In this review, an attempt is made to critically evaluate the chemical, physical, and biological synthesis of silver nanoparticles (AgNPs) as well as their efficacy in the field of theranostics including microbiology and parasitology. Moreover, an outlook is also provided regarding the performance of AgNPs against different biological systems such as bacteria, fungi, viruses, and parasites (leishmanial and malarial parasites) in curing certain fatal human diseases, with a special focus on cancer. The mechanism of action of AgNPs in different biological systems still remains enigmatic. Here, due to limited available literature, we only focused on AgNPs mechanism in biological systems including human (wound healing and apoptosis), bacteria, and viruses which may open new windows for future research to ensure the versatile application of AgNPs in cosmetics, electronics, and medical fields.
The focus of this review is to provide a comprehensive, well-elaborated, and up-to-date view about what is currently investigated about the antimicrobial and antiparasitic activities and various methods used for the synthesis of AgNPs. Besides, we strive to compile all the most recent investigations about the applications of AgNPs in many fields with a special focus on cancer and viral infection inhibition, and the toxicology of AgNPs. We strongly believe that this review will provide a handy mechanistic framework for the future analysis of AgNPs.
Nowadays, the applications of nanoparticles are tremendously increasing as they possess unique optical, chemical, electrical, electronic, and mechanical properties. These properties are attributed to their large surface area-to-volume ratio, which imparts them unique properties as compared to atoms/molecules as well as the bulk of the same material. Metallic particles, specifically AgNPs, are in focus due to their antimicrobial resistance as metal ions, while antibiotics are losing their effectiveness due to development of resistant strains of microbes. 1 Although the antimicrobial properties of AgNPs are extensively studied, their activities against other types of pathogens such as arthropods and different types of cancer cells have been evaluated only recently. AgNPs as therapeutic agents have achieved remarkable attention in the treatment of cancer, leishmania, malaria, and many other human diseases. However, there still remain many questions that are a matter of discussion for future research.
Currently, different metals including zinc, titanium and copper, 9 magnesium and gold, 10 , 11 and alginate 12 are used as antimicrobial agents, but among these AgNPs have been found to be the most efficient due to their outstanding antimicrobial properties. 13 In particular, nanosilver has been verified to have a great medicinal value attributable to its characteristic antibacterial, 13 , 14 antifungal, 9 antiviral, 15 antiprotozoal, 16 anticatalytic, 17 and antiarthropodal characteristics. 18 In cancer, metastasis is a great challenge to oncologists and clinicians due to the development of resistance to anticancer agents; 19 however, this problem can be overcome by nanoscale materials, especially nanosilver.
Various terminologies are used for silver particles such as colloidal silver, nano-silver, silver nanostructures, and silver nanoparticles (AgNPs). For the sake of convenience, we use the abbreviation AgNPs throughout this review. Nanotechnology is an advanced field dealing with the manufacturing of different kinds of nanomaterials having biomedical applications. 4 Due to a wide range of transmittable diseases caused by different pathogenic bacteria and their enhanced antibiotic resistance, many pharmaceutical companies and researchers are striving for synthesizing novel materials with enhanced antibacterial activity and reduced side effects. Currently, nanoscale materials have achieved considerable attention as novel antimicrobial agents due to their high surface area-to-volume ratio and distinct physical and chemical properties. 5 – 7 The extremely strong broad-spectrum antimicrobial property of AgNPs is the key direction for the improvement of AgNPs-based biomedical products, including bandages, catheters, antiseptic sprayers, textiles, and food storage containers. 8
“Nano” is a Greek word meaning small or dwarf. Nanoparticles can be defined as the particles ranging in size from 1 to 100 nm in either direction but can be considered as ranging up to several hundred nanometers. 1 These are actually aggregates of atoms, ions, or molecules. 1 In other words, “nano” is used to represent one billion of a meter or can be referred to as 10 −9 m. The concept of nanotechnology was first defined by Professor Norio Taniguchi in 1974, and since then, the field of nanotechnology has been receiving immense attention, especially from the early 1980s. 2 , 3
Graphene oxide (GO), an oxidized form of graphene, has been extensively used for various applications since the discovery of graphene in 2004. 207 Recently, GO has been utilized as a platform for growing NPs or attaching pre-synthesized NPs on its surface to produce NP-GO nanocomposites (NCs). Interestingly, NP-GO NCs exhibit enhanced surface enhanced Raman scattering, catalytic, and antibacterial properties compared to bare GO and NP. 208 – 213 Recent studies reported the fabrication of AgNPs-decorated GO as an effective antibacterial agent. 213 – 216
Over the past decade, silk fibroin has been applied in tissue engineering as a degradable surgical suture and scaffold 197 , 198 for its good biocompatibility, controllable biodegradability, and easy fabrication into different forms, such as fibers, films, gels, and three-dimensional scaffolds. 199 Silk fibroin is a good candidate for biomineralization. Previous works have indicated that silk fibroin regulates the morphologies of inorganic nanoparticles during the biomineralization process. 200 , 201 Silk fibroin contains 18 types of amino acid residues, including some polar amino acids such as tyrosine (Tyr). Tyr endows silk fibroin with the electron-donating property. The electron-donating property of the phenolic hydroxyl group of Tyr could directly reduce silver ion to AgNP. 202 Thus, it is possible to synthesize AgNPs through the reduction of Ag + by silk fibroin in situ to prepare the antibacterial silk film. Biopolymer film such as AgNPs silk is limited in its packaging application due to its poor mechanical property. To improve the mechanical property, biopolymer–polymer interaction is developed by blending natural biopolymers with polymers. PVA is a biodegradable, biocompatible, water-soluble, and nontoxic semicrystalline polymer. It offers good thermomechanical property, thermal stability, mechanical strength, and flexibility, as well as good optical and physical properties that are crucial for packaging application. 203 , 204 Moreover, PVA is approved by the US Food and Drug Administration as an indirect food additive for flexible food packaging. 205 , 206 The combination of AgNPs, silk fibroin, and PVA will be promising for active packaging.
Sericin, a globular glue protein, is exclusively produced in the middle silk gland of silkworm when silkworm spins a cocoon for protective and adhesive effects. 195 Silkworm cocoon is usually composed of about 75% fibroin and 25% sericin. However, sericin has been disposed of as a waste during the silk reeling process in the past few thousand years. It is not only a great waste of natural resources but also causes serious environmental pollution. Modern studies propounded that sericin performs a variety of biological activities, such as anticoagulation, antioxidant, antibacterial, and mitogenic effects, on mammalian cells. In regenerative medicines, it is usually mingled with functional polymers to form various scaffolds for biomedical purposes. 195
Cellulose is also one of the most important groups of polysaccharides, and due to its unique properties, cellulose is considered as an excellent template for the nanosilver formation. Both soluble and insoluble cellulose have been employed for the preparation of AgNPs, where alcohol and aldehyde groups performed an important role in the stabilization and reduction of silver ions 191 as presented in . Recently, the green synthesis of AgNPs using hydroxyl propyl cellulose (HPC) has also been reported. HPC plays a dual role (reducer and stabilizer) in the synthesis of AgNPs. 192 , 193 Insoluble cellulose was also investigated for the synthesis of AgNPs. Furthermore, it was indicated that various types of fibers were used in the silver salt solution. Meanwhile, experimental results showed that AgNPs of undetectable size to 160 and 50 nm were deposited on cotton and viscose fibers, respectively. Recently, cotton fabrics were investigated for the synthesis of the AgNPs. Trisodium citrate was used as a reducing agent at 90°C. Experimental results indicated that 20–90 nm AgNPs can be obtained. 194
It was also found that gum ghatti and gum kondagogu can be used as stabilizer and reducing agent for the synthesis of AgNPs. 180 , 181 Using gum ghatti, narrow-sized (4.8–6.4 nm) AgNPs were produced, whereas gum kondagogu produced 2–9 nm AgNPs. 181 Moreover, AgNPs of undetectable size to 25 nm (spherical) were also obtained from alkali-soluble xanthan and acacia. 182 , 183 Schizophyllan 184 and hyaluronic acid (HA) 185 were used as reducer and stabilizing agent for the synthesis of AgNPs. HA was analyzed chemically and thermally, and the results showed that 5–30 nm AgNPs can be obtained. 185 Similarly, carboxymethyl chitosan and N-phthaloyl chitosan were also used in the preparation of nanosilver. 186 – 188 In a recent report, it was investigated that under acidic medium, silver chitosan film was formed due to the mixing of both silver salts and chitosan. 189 Also, acidic medium and chitosan were used as chelating agents for AgNPs. 190
The starch solution (reducing/capping agent) and AgNO 3 (salt) have been used for the synthesis of AgNPs, and using these agents, stable AgNPs sized 10–34 nm were formed. These nanoparticles were stable in the aqueous solution at 25°C for around 3 months. 172 Similarly, small-sized AgNPs (5–20 and ≤10 nm) can be prepared using starch (stabilizer and capping agent) and NaOH solution having glucose (reducing agent). 173 , 174 Small-sized (1–21 nm) and spherical-shaped AgNPs have been synthesized using carboxymethyl starch in aqueous solution with a stability of more than 3 months at 25°C. 175 The alkaline solutions can also be used for solubilization of spherical nanoparticles in starch. 176 Recent studies revealed that ester of alginic acid (sodium and calcium alginate) can be used for the preparation of AgNPs. 177 , 178 Some studies also reported that the spherical-shaped and small-sized (1–4 nm) AgNPs can be obtained in 1 min from sodium alginate using water as solvent at 70°C. 179
Polysaccharides have been widely used for biomedical applications, as they are biocompatible and biodegradable. Polysaccharides are considered as excellent templates for the preparation of nanosilvers. Polysaccharides play a dual role, that is, reductants and/or capping agents, in the synthesis of AgNPs. For more than a decade, gentle heating of starch (capping agent) and β-d-glucose (reducing agent) has resulted in the formation of AgNPs. 171
Algae have been recently studied for the synthesis of AgNPs. Venkatpurwar and Pokharkar reported the formation of AgNPs from aquatic red algae using sulfated polysaccharides. These AgNPs were highly constant at broad pH range (2–10) and showed effective antibacterial activity against Gram-negative than Gram-positive bacteria. 167 El-Rafie et al extracted water-soluble polysaccharides from aquatic microalgae. These polysaccharides were used as both reducing and stabilizing agents for AgNPs formation. The colloidal solutions imparted antimicrobial activity when tested on cotton fabrics. 168 More recently, Salari et al were able to synthesize AgNPs from macroalgae Spirogyra varians through bio-reduction of silver ions. These AgNPs functioned as efficient bactericidal mediators in response to many pathogenic bacteria. 169 Some other algal species, namely Tetraselmis gracilis, Chaetoceros calcitrans, Isochrysis galbana, and Chlorella salina, can be successfully used for the AgNPs biosynthesis. 170
The spherical nanosilver can also be synthesized using Coriolus versicolor, but the reduction of AgNPs is time consuming (ie, 72 h; however, the duration could be reduced to 1 h by tailoring the reaction conditions using alkaline media at pH 10). The alkaline media play a vital role in the bio-reduction of silver ions, water hydrolysis, and interaction with protein functionalities. Furthermore, the S–H group from the protein plays an excellent role in the bio-reduction, whereas glucose molecule also plays a significant role in the reduction of AgNPs. 165 Aspergillus flavus can also be used to obtain stable nanosilver with more than 3 months of stability in aqueous solution. Meanwhile, the stabilizing agents released by fungal species ensure prevention of aggregation. 166
Balaji et al used an extracellular solution of Cladosporium cladosporiodes for the reduction of AgNO 3 to form spherical-shaped AgNPs of 10–100 nm size. They further reported that C. cladosporiodes released some organic materials, including polysaccharides, organic acids, and proteins, which were responsible for the formation of spherical crystalline AgNPs. 126 Penicillium spp. were also used for the production of AgNPs. 163 Soil-isolated Penicillium spp. J3 which has the ability to produce silver nanoparticles was used for the synthesis, and the AgNPs formation took place on the surface of the cells in which proteins acted as stabilizing agents. 164
Recent studies showed that AgNPs of size 5–25 and 5–50 nm could be extracellularly synthesized using Aspergillus fumigatus and Fusarium oxysporum, respectively. 161 , 162 The authors further reported that most of the nanoparticles were spherical in shape; however, rare triangular-shaped nanoparticles were also noticed. 161
Green and/or biogenic synthesis of any type of nanoparticles involves natural processes occurring in microorganisms like fungi, bacteria, and plants, as shown in . These organisms generate biocompatible nanostructures having excellent therapeutic potential. 131 Fungi-based synthesis of AgNPs is also eco-friendly and of low cost. In a recent study, two fungal strains, namely Penicillium expansum HA2N and Aspergillus terreus HA1N, were reported for the synthesis of AgNPs. The transmission electron microscopy result showed that 14–25 nm AgNPs were obtained from P. expansum, while 10–18 nm AgNPs were obtained from A. terreus. The efficacy of these AgNPs was further examined against different fungal species which demonstrated their strong antifungal potential. 62
Like other methods, metal precursors or silver salts are also used in the preparation of silver nanostructure from bacterial cultures. The production of AgNPs using sulfide (Ag 2 S) and oxide (Ag 2 O) of silver has also been reported by various studies. 31 , 156 In a recent report, the culture supernatant of bacterium Bacillus licheniformis was used to produce 40 and 50 nm AgNPs, respectively. 157 , 158 AgNPs of 1–6 nm size has also been produced using visible light emission from the supernatants of Klebsiella pneumoniae. 159 Furthermore, it was also found that Lactobacillus strains can be used for the production of AgNPs. 155 , 160 Recently, the bacterial strains of Aeromonas spp. SH10 and Corynebacterium spp. SH09 were screened for the biosynthesis of AgNPs. The authors concluded from their results that the bio-reduction of [Ag(NH 3 ) 2 ] + resulted in the production of monodispersed and stable AgNPs. 153
Klaus et al were the first to explore the ability of the bacterium Pseudomonas stutzeri AG259 to synthesize AgNPs. The bacteria exhibited a remarkable property of surviving in an extreme silver-rich environment, which might be the possible explanation for the accumulation of nanosilver. 150 Nanosilver particles have been synthesized using both Gram-positive and Gram-negative bacteria including the silver-resistant bacteria to form AgNPs. 151 Some bacteria have the ability to produce extracellular AgNPs, while others can synthesize intracellular AgNPs. Interestingly, some bacteria including Calothrix pulvinata, Anabaena flos-aquae, 152 Vibrio alginolyticus, 33 Aeromonas spp. SH10, 153 Plectonema boryanum UTEX 485, 154 and Lactobacillus spp. 155 have the ability to produce both extra- and intracellular AgNPs.
The biosynthesis of AgNPs was reported for the first time using identified antimicrobial molecules (gallic acid + apocynin) and (gallic acid + apocynin + quercetin) from the medicinal plant Pelargonium endlicherianum Fenzl., and these AgNPs had dramatically enhanced antimicrobial activity. 149
A simple, environmental-friendly, and cost-effective method has been developed to synthesize AgNPs using tea leaf extract. The synthesized AgNPs showed a good stability in terms of time-dependent release of silver ions. Due to the larger size and less silver ion release, the synthesized NPs showed low antibacterial activity against E. coli. 148
Babu and Prabu described the AgNP synthesis using a leaf extract of C. camphora, while the reduction was considered to be due to presence of the phenolics, terpenoids, polysaccharides, and flavonoids in the extract. 147
Chandran et al 140 and Li et al 141 reported the synthesis of AgNPs from the leaf extracts of Aloe vera and Capsicum annum plants, respectively. The rapid synthesis of AgNPs using the fruit extract of Carica papaya was demonstrated, and it was found that the synthesized nanoparticles were highly toxic against different multidrug-resistant (MDR) human pathogens. 142 Begum et al 143 were able to synthesize stable AgNPs of various shapes using black tea leaf extract. Extracellular synthesis of AgNPs was also carried out using leaf extract of Pine, Persimmon, Ginkgo, Magnolia, and Platanus plants. 144 In addition, AgNPs were successfully synthesized using the latex and seed extract of Jatropha curcas. 145 The compatibility of the bark and powder extracts of Curcuma longa was also checked towards the formation of AgNPs, and it was reported that bark extract could produce a higher amount of AgNPs compared to the powder extract. 146
The cubic- and hexagonal-shaped AgNPs of 31–40 nm size were obtained using the bark extract of Cinnamon zeylanicum. 137 Spherically shaped nanosilver sized 1–10 nm was synthesized from geraniol (C 10 H 18 O) compound isolated from two important medicinal plants, namely Pelargonium graveolens and Azadirachta indica. These AgNPs ablated fibrosarcoma Wehi 164 cancer cells. 86 In another study, ten different Cassia medicinal plant species were screened for the biosynthesis of AgNPs. It was also found that the leaves of P. graveolens and Cinnamomum camphora contained terpenoids which were responsible for the biosynthesis of AgNPs. 130 , 138 Among them, only the aqueous leaf extract of Cassia roxburghii supported the synthesis of stable AgNPs (35 nm size). These nanoparticles were further tested against human and plant pathogenic fungi, and they exhibited excellent result as compared to tested standard drugs. 139
In a recent study, the leaf extract of Ocimum sanctum was found to reduce Ag + ions into crystalline AgNPs having a size of 4–30 nm in 8 min. However, due to the presence of ascorbic acid in the plant leaves, the silver ions were readily reduced to metallic silver. The authors related the stability of the particles to the presence of proteins which played an important role as capping agents. The resulted AgNPs were effective against Escherichia coli and S. aureus. 136
Plant-based production is one of the most cost-effective and valuable alternative large-scale method for synthesizing AgNPs. 132 Researchers have put attempts and focused to synthesize AgNPs of varying size and shape using different plant extracts with a broad range of antimicrobial, anticancer, antiviral, and anticatalytic activities as shown in . Euphorbia hirta leaf extract was used for the synthesis of AgNPs resulting in the production of spherical nanoparticles sized 40–50 nm. These AgNPs showed strong activity against Bacillus cereus and Staphylococcus aureus bacterial strains. 133 Krishnaraj et al and Veerasamy et al were able to synthesize AgNPs of size 20–30 and 35 nm, respectively, using leaf extracts of the medicinal plants Acalypha indica and Garcinia mangostana. 134 , 135
The bio-based or green synthesis of AgNPs has great advantages over chemical and physical methods. Biologically synthesized AgNPs are eco-friendly, as no toxic reductants or stabilizing agents are used during the synthesis of nanoparticles. In biological systems, the health hazardous reducing and stabilizing agents can be substituted by essential biomolecules such as proteins 121 and carbohydrates, 122 which are locally produced by microbes including bacteria, 23 , 123 – 125 fungi 24 , 62 , 126 , 127 and yeast, 127 – 129 plants, 25 , 127 , 130 , 131 and lower organisms like algae. 127 , 130 , 131 The different reducing, capping, or stabilizing agents and silver salts or metal precursors which are used during biological method are presented in . Herein, we summarize some important biogenic synthesis or biological systems such as plants, bacteria, fungi, and algae using proteins and polysaccharides as reducing and stabilizing agents for the synthesis of AgNPs.
The sonoelectrochemistry technique utilizes the ultrasonic power primarily to manipulate the material mechanically. The pulsed sonoelectrochemical synthetic method involves alternating sonic and electric pulses. Electrolyte composition plays a crucial role in shape formation. 120 It was reported that silver nanospheres could be prepared by sonoelectrochemical reduction using a complexing agent, nitrilotriacetate, to avoid aggregation. 120
Previous studies demonstrated that UV light can assist in the reduction of silver ions to immobilize AgNPs on the surface of the polymer. Synthesis approach was applied to immobilize AgNPs in situ on the surface of sericin gel with the assistance of UV light. Scanning electron microscopy (SEM), X-ray diffractometry, Fourier-transform infrared spectroscopy, and differential scanning calorimetry were applied to characterize the surface tomography and structure of the AgNPs-modified sericin materials. Sericin gel was cut into small sheets and then soaked into 50 mM AgNO 3 solution. At the same time, sericin gel sheets were irradiated with a 365 nm UV light lamp (24 W) for 10, 30, and 60 min to make AgNPs immobilize on the surface of sericin gel, respectively. The collected AgNPs-modified sericin gel sheets were dried at room temperature, and then their surface tomography, structure, and antimicrobial activity were studied. 119
A simple and effective method, ultraviolet (UV)-initiated photoreduction, has been reported for the synthesis of AgNPs in the presence of citrate, PVP, poly (acrylic acid), and collagen. For instance, Huang and Yang produced AgNPs via photoreduction of AgNO 3 in layered inorganic laponite clay suspension which served as a stabilizing agent for the prevention of NPs aggregation. The properties of produced NPs were studied as a function of UV irradiation time. Bimodal size distribution and relatively large AgNPs were obtained using UV irradiation for 3 h. Further irradiation disintegrated the AgNPs into smaller-sized particles with a single distribution mode until a relatively stable size and size distribution were obtained. 117 Silver NPs (nanosphere, nanowire, and dendrite) have been prepared by UV irradiation photoreduction technique at room temperature using poly (vinyl alcohol) (PVA) (as protecting and stabilizing agent). The concentration of both PVA and AgNO 3 played a significant role in the growth of the nanorods and dendrites. 118
Some studies documented that AgNPs were formed when bulk materials in solution were subjected to laser ablation technique. 22 , 113 – 115 Meanwhile, it was also found that silver nanospheroids sized 20–50 nm can be obtained by the same technique in pure water with femtosecond laser pulses at 800 nm. 71 Laser ablation method has an advantage over other techniques because there is no need to add any reagent to solutions. Thus, laser ablation technique is useful for the production of uncontaminated and pure metal colloids. 116
Tsuji et al used the small ceramic heater and laser ablation method, respectively, to synthesize AgNPs. 116 Later on, investigators successfully synthesized colloidal AgNPs in a metal solution with no chemical reagent added. Furthermore, using arc discharge method, Tien et al produced AgNPs having 20–30 nm size in pure water without the addition of any stabilizers or surfactants. 103
The most important physical techniques frequently used for the preparation of AgNPs include evaporation/vapor condensation, 22 , 102 , 108 arc discharge, 109 energy ball milling, 110 and direct current magnetron sputtering method. 23 Compared to chemical methods, physical methods are generally less time consuming and do not involve any type of hazardous chemicals. 110 However, high energy consumption and requirement of long time for thermal stability are still the bottlenecks of these methods. 22 , 111 , 112
Irradiation is another method to prepare AgNPs. Abid et al concluded from their study that AgNPs of definite shape and size can be produced using laser irradiation of surfactant and an aqueous solution of silver salt. 106 Sudeep and Kamat successfully induced the synthesis of AgNPs in ethanol/toluene organic solution. 107 However, more investigations are needed to further address the possible in vitro and in vivo potential toxicities that can be the outcomes of the chemical method used for synthesizing AgNPs.
Similar to chemical reduction method, the silver nanostructure can be synthesized by an electrochemical method. Using this approach, small-sized (10–20 nm) AgNPs with spherical shape can be produced. 78 Furthermore, using crystals of zeolite, monodisperse silver nanospheroids of size 1–18 nm have been formed by electrochemical reduction. 105 However, using organic and aqueous interface, polyphenylpyrrole-coated silver nanospheroids of size 3–20 nm can be obtained by electrochemical method. 77
In their recent study, Zhang et al reported that colloidal silver could be synthesized through the chemical reaction of polymethylene bisacrylamide aminoethyl piperazine with terminal dimethylamine groups (HPAMAM-N (CH 3 ) 2 ). Later on, it was documented that these groups have strong reducing and stabilizing potential. 104 In another case study, it was demonstrated that polyol process and modified injection technique could produce spherical, highly mono-dispersed AgNPs of controllable size. The reaction temperature and rate of injection were important factors in this method to obtain uniform AgNPs of reduced sized. AgNPs with 17±2 nm diameter were obtained at 100°C and 2.5 mL/s injection rate. 73
The commonly reported stabilizing/capping agents include surfactants and polymeric compounds such as polyvinyl pyrrolidone (PVP), PEG, poly(N-isopropylacrylamide), poly (methyl methacrylate), poly (methacrylic acid), and collagen. 101 , 102 Among these stabilizers, the alcohols, thiols, amines, acidic functional groups, and surfactants protect the nanoparticles from sedimentation as well as protect them from losing their surface properties. Silver nitrate (AgNO 3 ) is the most significant silver salt frequently used for the preparation of AgNPs, and as compared to other salts, it is chemically stable, easily available, and cost-effective. 103 A detailed summary of reducing, capping, or stabilizing agents and silver salts or metal precursors used in biological, chemical, and physical methods is provided in .
AgNPs can be synthesized by chemical reduction, 92 electrochemical technique, 20 irradiation-assisted chemical method, 93 and pyrolysis; 21 of these, chemical reduction has been the most common route to synthesize nanosilver. Three main components, namely organic and inorganic reducing agents, capping agents or stabilizers, and metal precursors or silver salts, are used in this method ( ). Hydrogen gas, 94 borohydride, 80 , 94 , 95 citrate, 96 ascorbic acid, 97 hydrazine compounds, polyol process, Tollens’ reagent, N,N-dimethylformamide, and poly (ethylene glycol) (PEG)-block polymers are the reducing agents most frequently used in this method. These reductants bring about a reduction of silver ions (Ag + ) to metallic silver (Ag 0 ) followed by agglomeration into oligomeric clusters in aqueous and nonaqueous solutions. Finally, these clusters form metallic colloidal nanosilver. 98 – 100 Borohydride has been extensively used for reduction process because of its strong and rapid reductant properties as well as its ability to act as a stabilizer to evade aggregation of AgNPs throughout decaying. 94
AgNPs can be synthesized by various methods ( ) including chemical synthesis, 8 , 20 – 22 physical techniques, 8 , 22 , 23 and green or biological methods. 24 – 26 Some important examples for biological, physical, and chemical synthesis of AgNPs are mentioned in .
Antimicrobial activities of AgNPs as presented in and have been known for many centuries, but their assessment on a scientific basis has only been realized in recent years. Sondi and Salopek-Sondi for the first time depicted AgNPs performance against E. coli, to propose a possible enlightenment of the observed action of AgNPs on bacteria. The authors revealed that the appearance of “pits” in bacterial cell wall and accumulation of AgNPs in the cellular membrane resulted in an enhanced permeability of cell wall and eventually induced bactericidal activity.218
Open in a separate windowDevi and Joshi evaluated 53 strains of various fungi for the mycosynthesis of AgNPs and showed considerable effectiveness of AgNPs against Streptococcus pyogenes, Salmonella enterica, S. aureus, and Enterococcus faecalis.219 Moreover, the mycosynthesized nanoparticles also exhibited potential antibacterial activity and synergistic effect with erythromycin, chloramphenicol, methicillin, and ciprofloxacin against Enterobacter aerogenes and K. pneumoniae66 and with antibiotics ampicillin, tetracycline, gentamycin, and streptomycin against E. coli, S. aureus, and Pseudomonas aeruginosa.220 The antibacterial activity of AgNPs strongly depends on the size of the silver particles as reported in previous reports. AgNPs with a smaller size have high activity due to a relative increase in contact surface.221
Shameli et al reported size-based bactericidal potential of various AgNPs prepared in PEG against S. aureus and Salmonella typhimurium bacteria using disc diffusion method. AgNPs were found to be very effective and cause momentous inhibition of both strains. They summarized that the bactericidal potential of AgNPs in PEG can be tuned by controlling the size of nanoparticles, since smaller particles have a relatively greater contact surface area than larger particles. The factors that are influencing the activity of AgNPs (size, shape, concentration, UV radiation, and combination with different antibiotics) should be taken into account during the preparation processes and medicinal applications of AgNPs.222 Similarly, investigations by Raheman et al and Gade et al had already demonstrated the biocidal potential of AgNPs, respectively.67,223 Silver bionanocomposite films having a size less than 20 nm were tested against E. coli, P. aeruginosa, S. aureus, and Micrococcus luteus. These silver composites exhibited satisfactory antibacterial properties.224
In recent studies, spherical-shaped 20, 18, and 15 nm AgNPs were prepared. The experimental result showed that all AgNPs were active against different strains of bacteria.13,17 In another study, AgNPs having a spherical shape and ranging in size from 5 to 30 nm and crude latex aqueous extract were tested against different bacterial pathogens such as Enterococci spp., B. cereus, Shigella spp., P. aeruginosa, S. aureus, K. pneumoniae, and E. coli. These biosynthesized AgNPs were found to have the capability of enhancing the antimicrobial activity compared to crude latex aqueous extract.225 The nanoparticles assumed spherical geometry and were often aggregated into small particles with quite a uniform size of 12.50–41.90 nm. These AgNPs showed exceptional antibacterial property against different strains of bacteria. Afterwards, they were found to be more effective against E. coli and K. pneumoniae than against E. faecalis and S. mutans. This differential activity may possibly be due to the difference in bacterial cell wall structure.226
Recently, AgNPs with an average uniform size of 5 nm were tested against bacteria. Results indicated that the efficiency of antibiotics was improved in the presence of AgNPs against test strains. The activity of AgNPs was more pronounced with ampicillin against the Gram-negative bacteria Shigella flexneri and P. aeruginosa, and vancomycin against the Gram-positive bacteria Streptococcus pneumoniae and S. aureus. More interestingly, these antibiotics exhibited higher antimicrobial efficiency in association with AgNPs. These results suggested that AgNPs could be used as an adjuvant for curing various infectious diseases caused by bacteria.4 AgNPs which were synthesized by the green method and their antibacterial properties were studied using diffusion method. The concentration of AgNPs was varied as 25, 50, 75, and 100 μg/mL. The highest efficiency of AgNPs was found against S. aureus (23 mm) and E. coli (28 mm). The moderate activity was obtained against Salmonella typhi (18 mm) followed by M. luteus (15 mm) and P. aeruginosa (13 mm).19
AgNPs, having a size of 26 nm, have been reported to be efficient against E. faecalis CCM 4224, S. aureus CCM 3953, E. coli CCM 3954, and P. aeruginosa CCM 3955. The modified antibacterial activity of silver NPs was considerably improved as confirmed by minimum inhibitory concentration (MIC) values ranging from 6.75 down to 0.84 μg/mL.227 In another study, the growth rates of bacteria were studied under varying AgNPs concentrations, incubation temperatures, times, and pH. E. coli and S. aureus were shown to be substantially inhibited by AgNPs, and the antibacterial activity of AgNPs did not change with pH or temperature.228
AgNPs in montmorillonite were prepared, and their antibacterial activities against S. aureus and methicillin-resistant S. aureus (Gram-positive bacteria) and E. coli, E. coli O157:H7, and K. pneumoniae (Gram-negative bacteria) were tested by the disc diffusion method using Mueller–Hinton agar. The smaller AgNPs exhibited significantly higher antibacterial activity.229 More recently, cream formulations of AgNPs and AgNO3 were prepared, and their antibacterial activity was evaluated on human pathogens (S. aureus, Proteus vulgaris, E. coli, P. aeruginosa, and Candida albicans) and a plant pathogen (Agrobacterium tumefaciens). The antimicrobial studies concluded that AgNPs have 200 times more inhibitory effect compared to AgNO3. The AgNPs act by damaging the cell membrane of E. coli, which was confirmed by SEM study.230
The antibacterial activity of AgNPs was tested against nine human diseases-causing Gram-negative bacteria and one Gram-positive bacteria. AgNPs extracts had the capability to enhance antibacterial activity against all tested strains compared to the extracts alone. AgNPs were more bactericidal in liquid than in solid medium, probably due to better contact with bacterial cells in a liquid state. Maximum zone of inhibition was 19 mm for nanoparticles of leaves on P. aeruginosa (ATCC278223) and 18 mm for latex nanoparticles on S. flexneri (ATCC12022). The minimum zone of inhibition was 7 mm for both nanoparticles of leaves and latex on S. typhi (ATCC19430) and S. typhimurium (ATCC14028), respectively.231
The leaf extract of Lantana camara was used for the biosynthesis of AgNPs. These nanoparticles were evaluated for catalytic and antibacterial activities. The biosynthesized nanosilver had excellent potential against the tested strains including E. coli, Pseudomonas spp., Bacillus spp., and Staphylococcus spp. Moreover, these AgNPs also showed higher catalytic activity in the reduction of methylene blue observed using UV–vis spectrophotometer.232 Spherical nanosilver sized 10–15 nm was synthesized from fresh spinach leaves. These nanoparticles had strong bactericidal potential and good catalytic property toward methyl red and methylene blue.233
A recent study on the effect of AgNPs (13.4 nm) against E. coli and S. aureus found their MIC values to be below 6.6 nM and above 33 nM, respectively.234 Another study was conducted against the bacterium E. coli. The results showed that AgNPs (16 nm) had the ability to inhibit E. coli colony-forming unit at a concentration of 60 μg/mL.235 Furthermore, the activity of some important dendrimer (poly-amidoamine) Ag-composites has also been reported against E. coli, S. aureus, P. aeruginosa, Klebsiella mobilis, and Bacillus subtilis.104
The antimicrobial property of AgNPs is most exploited in the medical field, though their anti-inflammatory nature is also considered immensely useful. Initial studies have suggested that the acceleration of wound healing in the presence of nanoparticles is due to the reduction of local matrix metalloproteinase activity and the increase in neutrophil apoptosis within the wound.
Recent evidence suggests that nanosilver has a potent anti-inflammatory effect236–238 and accelerates wound healing.239,240 Silver has long been known to possess antibacterial activity and has been used throughout history, from Hippocrates’ early treatment of ulcers to C.S.F. Crede’s treatment of gonococcal infections in newborns. Silver is still used clinically, and nanosilver is emerging as a valuable tool in the therapeutic armory ( ). Silver sulfadiazine is the gold standard for the topical treatment of burn patients.241 The resurgent interest in silver and nanosilver has been motivated by the emergence of rampant antibiotic-resistant bacteria and the increasing prevalence of hospital-acquired bacterial infections. The use of silver has been severely limited by the toxicity of silver ions to humans; however, nanotechnology has facilitated the production of smaller silver particles with increasingly large surface area-to-volume ratios, greater efficacy against bacteria,242,243 and most importantly, lower toxicity to humans.244
Nanocrystalline silver wound dressings have been commercially available for over a decade (eg, Acticoat™) and are in current clinical use for the treatment of various wounds, including burns,240,245,246 toxic epidermal necrolysis,247 Stevens–Johnson syndrome,248 chronic ulcers,237 and pemphigus.248 Typical dressings consist of two layers of polyethylene mesh forming a sandwich around a layer of polyester gauze. Typical nanocrystalline coatings are 900 nm thick with a crystallite size of 10–15 nm236 and are applied to the polyethylene layer.
In 2008, Kim et al demonstrated the potential of AgNPs against 44 strains of six fungal species, namely Candida tropicalis, C. albicans, Candida glabrata, Candida krusei, Candida parapsilosis, and Trichophyton mentagrophytes. The AgNPs were found active against various strains of T. mentagrophytes and Candida spp.249 Similarly, Velluti et al found that nanosilver complexes [Ag2(SMX)2] showed good activity against 10 fungal strains, namely C. tropicalis (C 131), C. albicans (ATCC 10231), Cryptococcus neoformans (ATCC 32264), Saccharomyces cerevisiae (ATCC 9763), A. fumigatus (ATCC 26934), A. flavus (ATCC 9170), Aspergillus niger (ATCC 9029), dermatophytes including Trichophyton rubrum (C 113), T. mentagrophytes (ATCC 9972), and Microsporum gypseum (C 115).250
Gajbhiye et al reported the efficiency of biogenic AgNPs against Pleospora herbarum, Phoma glomerata, Fusarium semitectum, Trichoderma spp., and C. albicans. Furthermore, they also reported the synergistic effects of AgNPs in association with fluconazole.251 In 2009, Jo et al demonstrated the antifungal potential of silver ions and nanoparticles against two plant pathogenic fungi, Magnaporthe grisea and Bipolaris sorokiniana. The fungicidal potential of AgNPs in combination with various heterocyclic compounds like phthalazine, thiazolidine, hydrazide, pyrazolo, tetrazolo, and pyridazine derivatives was studied against C. albicans and A. flavus, and the AgNPs were found to have significant fungicidal activity against tested organisms.252
Recently, six fungal species, namely Penicillium brevicompactum, A. fumigatus, Mortierella alpina, C. cladosporoides, Chaetomium globosum, and Stachybotrys chartarum, were selected for the study of the antifungal activity of AgNPs. The growth rates of all tested fungal species, except Mortierella spp., were affected by the addition of AgNPs, which caused the limitation of Chaetomium and Stachybotrys on gypsum products. Each fungus showed a distinct response to applied AgNPs depending upon the concentration and the rate of Ag ions released into the environment.253
In 2010, Jaidev and Narasimha demonstrated the antifungal (A. niger) and antibacterial (Staphylococcus spp., E. coli, Bacillus spp.) activities of AgNPs. They reported that nanosilver has excellent inhibitory activity against A. niger confirming the maximum activity as compared to Bacillus spp. (0.8 cm), Staphylococcus spp. (0.9 cm), and E. coli (0.8 cm).69 Meanwhile, Nasrollahi et al studied the fungicidal potential of AgNPs against S. cerevisiae and C. albicans. Their results were productive confirming the excellent potential of AgNPs as compared to standard antifungal agents (viz. fluconazole and amphotericin B).254 Savithramma et al prepared AgNPs using a different extract of medicinal plants, Shorea tumbuggaia, Boswellia ovalifoliolata, and Svensonia hyderobadensis, to evaluate their antifungal activity against A. niger, Curvularia spp., A. flavus, Fusarium spp., and Rhizopus spp. The results confirmed that all biogenic AgNPs showed considerable antifungal activity against various fungal spp. The AgNPs synthesized with S. hyderobadensis exhibited higher activity as compared to AgNPs synthesized using the other two plants.255
Kaur et al reported the fungicidal potential of silver and chitosan nanoparticles against A. flavus, Rhizoctonia solani, and Alternaria alternata from chickpea seeds.256 In 2012, Arjun and Bholay also demonstrated the momentous efficiency of AgNPs against T. rubrum, C. albicans, and A. fumigatus.257 Xu et al also tested nanosilver and natamycin against 216 strains of fungi from patients suffering from severe keratitis. These included 82 isolates of Aspergillus, 112 isolates of Fusarium, and 10 isolates of Alternaria. Results demonstrated that AgNPs had higher activity as compared to natamycin.258 Similarly, Dar et al studied the biocidal potential of AgNPs synthesized from Cryphonectria spp. against S. typhi, E. coli, S. aureus, and C. albicans, concluding that AgNPs can be used as potential antifungal agents.64
More recently, the antifungal activity of mycosynthesized AgNPs was tested for the first time against plant pathogenic fungi. AgNPs displayed good antifungal activity against Colletotrichum spp. (12.63 mm) followed by R. solani (12.03 mm) and Cochliobolus lunata (11.23 mm) at 1 mg/mL concentration. The nanoparticles were less effective against Fusarium spp. (9.37 mm).259 In another study, AgNO3 was tested against three fungi namely Trichoderma spp. (ATCC 18648), Mucor spp. (ATCC 48559), and A. niger (ATCC 6275), and it was found to exhibit good antifungal activity.260
The antifungal activity of AgNPs against C. tropicalis and C. albicans was also investigated. Stable nanoparticles of size 12.5±4.9 nm (mean ± SD) were obtained, which presented high activity against Candida spp.261 The spherical and polydispersed AgNPs, ranging in size from 4 to 36 nm and 8 to 60 nm, respectively, were applied against superficial mycoses caused by T. rubrum, Malassezia furfur, C. albicans, and C. tropicalis. The AgNPs exhibited highest antifungal activity against T. rubrum and the least against M. furfur and C. albicans as compared to others.262
C. glabrata and C. krusei were exposed to spherical nanoparticles (19 nm) with positive surface charge. The MIC50 values were 0.1–l g mL−1 AgNPs, and minimum fungicidal concentration (MFC) values were 0.25 and 0.5 g mL−1 for C. glabrata and C. krusei, respectively.263 Meanwhile, another research confirmed that concentrations of AgNPs between 10 and 25 μM reduced the growth rates of the tested fungus and bacteria and showed the bactericidal/fungicidal activity by delaying the exponential and stationary phases. However, complete inhibition of the growth of C. albicans MTCC183 was found at a concentration of 10 μM AgNPs.264
A more recent report showed that AgNPs (spherical, 1–40 nm) had excellent antifungal activity against R. solani cultures by inhibiting 83% of the mycelium growth at 25 μg/mL concentration.265 In another study, several essential oils were tested for their antifungal activity. The oil isolated from the bark of Cinnamomum cassia had the highest activity against MIC and MFC values for all tested strains in the range of 0.0006%–0.0097% (v/v) and 0.0012%–0.019% (v/v), respectively.
Further studies were carried out about the antifungal activity of AgNPs against some Candida spp. The fungicidal efficacy of AgNPs functionalized with PVP was established. The PVP-functionalized silver particles demonstrated no damage to fungi until the exposure time was 24 h. After 24 h, no viability of fungal cells was observed. The work revealed that Ag particles aggregate outside the fungal cells, releasing free silver ions and thus inducing cell necrosis through the reduction process.266 Naz et al synthesized silver particles capped with 5-amino-β-resocyclic acid hydrochloride dehydrate (AR). They analyzed their nanostructures before and after conjugation to silver metal for in vitro antifungal, antibacterial, antioxidant, and enzyme inhibitory properties. The results indicated that the fungicidal activity of Ag, AR, and Ag AR were not momentous as compared to the dithane-M45 (standard fungicide).267
AgNPs have been popular for their antibacterial and antifungal activities. However, recent studies have exploited AgNO3 potential in neoplastic maladies. Recently, eco-friendly AgNPs were synthesized from the leaf extracts of Vitex negundo268 and Sesbania grandiflora, and their efficacy was tested against human colon cancer cell lines HCT15 and MCF-7, respectively. The results demonstrated that AgNPs obtained from V. negundo showed antiproliferative effects on cancer cell line, reduced DNA synthesis, and induced apoptosis.268 Similarly, nanosilver obtained from S. grandiflora also caused cytotoxicity, oxidative stress, and apoptosis in tumor cells.269 Moreover, green-synthesized AgNPs from the leaves extract of Podophyllum hexandrum and Suaefa monoica were examined and found to show cytotoxic activity and apoptotic effect, respectively.270,271
Piao et al demonstrated that OH radicals released by the AgNPs attacked cellular molecules including DNA, proteins, and lipids to induce oxidative damages.272 In another report, it was shown that AgNPs exhibited toxicity due to some factors such as dose, size of particles, and time. In the case of MCF-7 cell culture, the toxicity was due to the dose of AgNPs. AgNPs also caused cellular damage in Human Epidermoid Larynx (Hep-2) cell line through reactive oxygen species (ROS) formation.273 Lima et al greenly synthesized nanosilver and evaluated its genotoxicity and cytotoxicity.63 Also, Durán et al studied the potential of biosynthesized AgNPs. These nanosilver particles interacted with DNA, proteins, and cellular organelles via ROS, and induced necrosis and apoptosis in the tumor cells.274
New nanocrystalline silver with a structural size of 8 nm customized with TAT cell penetrating peptide (AgNP-TAT) exhibited higher antitumor property in both nonresistant and MDR cells without any discrimination. The AgNP-TAT displayed outstanding efficacy in killing tumor cells, that is, up to 24-fold higher than pristine AgNO3 without TAT alteration. Moreover, the AgNP-TAT also displayed considerable reduction in adverse toxic effects, in vivo.275
Dimocarpus longan Lour. peel aqueous extract (acts as reducing and stabilizing agent) was evaluated for the synthesis and anticancer and antibacterial effects of AgNPs. The antibacterial activities of AgNPs were evaluated using dilution method, whereas their efficacy against human prostate cancer (PC-3) cells was in vitro evaluated via blue assay and Western blot by the expression of phosphorylated stat 3, caspase-3, bcl-2, and survivin. These nanoparticles had the face-centered cubic structure (size 9–32 nm) and exhibited great bactericidal potential against both Gram-positive and Gram-negative strains of bacteria.276
In another study, Malus domestica and Origanim vulgare extracts were used for the synthesis of nanosilver. The M. domestica extract-biosynthesized silver had considerable effects on MCF-7 breast cancer cells, whereas silver synthesized from O. vulgare aqueous extracts showed dose-dependent response against human lung cancer A549 cell line.277,278
In a recent study, AgNPs were obtained from the stem bark extract of Moringa olifera. These biosynthesized AgNPs were tested for anticancer properties. The flow cytometry results showed apoptosis induced through ROS generation in HeLa cells.279 The rhamnolipids were isolated from P. aeruginosa strain JS-11 and used for the biosynthesis of Rh-AgNPs. These nanosilver particles were tested against MCF-7 human cells.280 Furthermore, caffeic acid-mediated spherical nanosilver particles of 6.67±0.35 nm size were used against cancer cells. The results showed that AgNPs efficiently inhibited the growth of HepG2 cells via apoptosis induction.281
Recently, spherical-shaped (6.2±0.2 nm) silver-(protein-lipid) nanoparticles (Ag-LP-NPs) were obtained using the seed extract of Sterculia foetida. These eco-friendly Ag-LP-NPs showed antiproliferative activity against HeLa cancer cell lines and also showed potential toxicity in a dose-dependent manner.282 More recently, biogenic AgNPs were obtained from the flower extract of Plumeria alba (frangipani) known as frangipani AgNPs (FS NPs). These FS NPs had a cytotoxic effect on COLO 205 which was determined by MTT assay, and after 24 and 48 h of incubation, the IC50 concentration was found at 4 and 5.5 μg/mL, respectively. Furthermore, the FS NPs cytotoxic affect on COLO 205 cells was associated with the loss of membrane integrity and chromatin condensation that have a great role in the induction of apoptosis as evidenced by acridine orange/ethidium bromide staining.283
On the other hand, it was also demonstrated that AgNO3 and metal-based nanoparticles (AgNPs) had strong potential for cytotoxic, antiproliferative, and apoptotic property in H-ras 5RP7 cells and cervical cancer, respectively.284,285
Biosynthesized nanosilver from the extract of Pterocladiella capillacea (11.4±3.52 nm) and P. aeruginosa (13–76 nm) showed great potential against human hepatocellular carcinoma (HepG2) cell lines and human cervical cancer cells (HeLa), respectively.286,287 In another study, it was found that green-synthesized nanosilver (45±0.15 nm) from novel Nocardiopsis spp. had potent activity against in vitro human cervical cancer cell line. The IC50 value was recorded in the range of 200 μg/mL of AgNPs against HeLa cancer cells.288 It was also found that the plumbagin-caged nanosilver induced ~80% cell death at a concentration of 2.5 μM, whereas no cytotoxicity was observed for normal cells.289
A study published by Yeasmin et al demonstrated that AgNPs with controlled shape are more effective against many types of cancer cell lines. They stabilized the shape of spherical silver nanoparticles by interaction with natural gum and then screened against cervical cancer cell lines (HeLa), lung cancer (A549), and mice macrophage or RAW 264.7 and found that the particles effectively killed these cell lines in a dose-dependent manner.290 Venil et al reported flexirubin (a bacterial pigment)-mediated silver nanoparticles for the first time that were highly cytotoxic (IC50 value of 36 μg/mL) against human breast cancer cell lines (MCF-7).291
Nowadays, chitosan-based biosynthesized silver nanoparticles are mostly synthesized and used against different cancer cell lines. A study performed by Venkatesan et al demonstrated that porous chitosan-alginate-biosynthesized AgNPs exhibited cytotoxic effects against breast cancer cell line MDA-MB-231 (IC50 =4.6 mg).292 A recent study demonstrated that loaded quinazolinone polypyrrole/chitosan silver chloride NC had active anticancer efficacy against Ehrlich ascites carcinoma cells.293 The chitosan-silver hybrid nanoparticles were proven to induce apoptosis in HepG2 cells by downregulating BCL2 gene and upregulating P53.294
AgNPs have received enormous attention for their bactericidal potential, while the antiviral activities of metal nanoparticles remain an emergent area. The potential of AgNPs was studied in both prokaryotic and eukaryotic organisms,295 and it was reported that small-sized AgNPs of around 25 nm or less had outstanding potential in viral infection inhibition.296 The aqueous extract of Ricinus communis was used for the synthesis of nanoparticles, which resulted in AgNPs sized 1,000 nm. Smaller-sized (5–20 nm) AgNPs were obtained from fungi. The results indicated that the small-sized AgNPs had an excellent ability to decrease the infection potential of herpes simplex virus types (HSV) 1/2 and human parainfluenza virus type 3.297
Baram-Pinto et al investigated the inhibitory effect of AgNPs against HSV-1 and demonstrated that sulfonate-capped nanosilver inhibited HSV-1 infection. Furthermore, they demonstrated that AgNPs prevented the attachment and entry of virus into a cell or prevented the cell from spreading the virus. The heparan sulfate is a cellular primary acceptor of HSV, and thus competes with the virus for attaching to the cell and the potential was enhanced due to the presence of the inner core AgNPs.298 This study also demonstrated the virucidal action of AgNPs. These nanoparticles exhibited anti-HIV activity at an early stage of viral infection and also prevented the further replication of HIV-1.299 Furthermore, the viruses and other microbial strains were grown under multicycler growth condition in the absence or presence of colloidal silver to check the antimicrobial property. As expected, no viral growth was seen with any strains tested.300
A recent study also showed that T lymphocyte (T)-tropic and macrophage (M)-tropic strains of HIV-1 were extremely susceptible to the AgNPs coated with polyurethane condom.15
In a recent study, different types of nanosilver particles were biosynthesized from F. oxysporum (4–13 nm), Curvularia spp. (5–23 nm), and Alternaria and Phoma spp. (7–20 nm). Silver particles produced from F. oxysporum and Curvularia spp. had exceptional antiviral activity but were less cytotoxic to Vero cells, whereas particles produced from Alternaria and Phoma spp. showed moderate virucidal action. This study also confirmed that small-sized nanoparticles have excellent ability to inhibit the replication of virus as compared to larger ones.297
More recently, the tannic acid-modified AgNPs in the range of 13, 33, and 46 nm were found to reduce HSV-2 infectivity in vivo and in vitro. In particular, tannic acid in the same amount also showed somewhat in vivo potential against the virus. Therefore, tannic acid-modified nanosilver was used as an antimicrobial agent in addition to cream or protective gel used for oral herpes infections treatment.301
According to the WHO, leishmaniasis is the sixth most infectious disease.302 Leishmaniasis is one of the most abandoned tropical infections around the globe, with occurrence in 88 countries and a predictable number of 500,000 cases of visceral form and 1.5 million cases of cutaneous leishmaniasis.303 Rossi-Bergmann et al demonstrated the potential function of biosynthesized AgNPs (using F. oxysporum) against Leishmania amazonensis promastigotes both in vivo and in vitro. They also compared the biologically and chemically synthesized AgNPs. Their results demonstrated that biosynthesized nanosilver was four times more active as compared to chemically produced AgNPs in vitro, while the in vivo results showed it was even more effective.304
The protozoal vector-borne diseases are the most common and important infections in developed regions, resulting in over one million deaths from malaria on yearly bases, worldwide.305 To control the malaria vector, researchers strive to discover innovative approach against antimalarial agents. Among various antimalarial drugs, AgNPs have also been evaluated against malarial parasites and reported with promising potential against malaria. In recent studies, the biologically synthesized AgNPs from Andrographis paniculata Nees. (Acanthaceae) ~55 nm in size306 and Catharanthus roseus leaves (approximate size 35–55 nm) were tested against P. falciparum.307 In another study, the higher antimalarial potential of AgNPs was reported. The AgNPs were bio-reduced in 5% Cassia occidentalis leaf broth against chloroquine-sensitive and chloroquine-resistant strains of P. falciparum and malarial vector Anopheles stephensi.232
The global "Nano Silver Powder Market" report indicates a |Consistent Growth of 2024| pattern in recent times, which is expected to continue positively until 2032. A prominent trend in the Nano Silver Powder market is the increasing demand for products that are environmentally sustainable and eco-friendly. Another significant observation in this market is the rising incorporation of technology to elevate both the quality and efficiency of products. State-of-the-art technologies such as artificial intelligence, machine learning, and blockchain are being harnessed to create innovative products that surpass conventional options in terms of both effectiveness and efficiency. The Nano Silver Powder Market Research Report for 2024 highlights trends, growth prospects, and potential scenarios up to the year 2032.
The Nano Silver Powder market provides detailed insights into the five major elements (size, share, scope, growth and potential of the industry). It offers valuable information to help businesses identify opportunities and potential risks within the market. This detailed report is spread across 105 pages, ensuring an in-depth analysis of the subject matter.
Overall, the Nano Silver Powder market is poised for continued expansion in the coming years due to the increasing demand for sustainable and innovative products, as well as the widespread adoption of technology. By 2032, the global Nano Silver Powder market size is projected to reach multimillion figures, displaying an unexpected compound annual growth rate between 2024 and 2032 when compared to the figures observed in 2021.
Companies Covered: Nano Silver Powder Market Ask for A Sample Report
These companies have the potential to drive market growth through various strategies. They can focus on offering innovative and high-performance products, taking advantage of advancements in technology. Additionally, expanding their distribution channels to target new customers would be beneficial. Strategic partnerships and collaborations can also be pursued to strengthen market presence and enhance competitiveness.
Who is the largest manufacturers of Nano Silver Powder Market worldwide?
The global Nano Silver Powder market size is segmented on the basis of application, end user, and region, with focus on manufacturers in different regions. The study has detailed the analysis of different factors that increase the industries growth. This study also provides the scope of different segments and applications that can potentially influence the industry in the future. Pricing analysis is covered in this report according to each type, manufacturer, regional analysis, price. Nano Silver Powder Market Share report provides overview of market value structure, cost drivers, various driving factors and analyze industry atmosphere, then studies global outline of industry size, demand, application, revenue, product, region and segments.
What is Nano Silver Powder?
Nano Silver Powder is a kind of ultra-fine nano-silver particles powder , prepared through special production process. It has a wide range of applications with its excellent performance. It can be used for sterilization, can also be used as a catalyst, etc.
According to 2024 New survey, global Nano Silver Powder market is projected to reach USD 46 million in 2029, increasing from USD 32 million in 2022, with the CAGR of 5.3% during the period of 2023 to 2029. Influencing issues, such as economy environments, COVID-19 and Russia-Ukraine War, have led to great market fluctuations in the past few years and are considered comprehensively in the whole Nano Silver Powder market research.
Nano silver powder is a promising novel material with widespread applications, making significant strides in sectors such as healthcare, electronics, and environmental protection. The market has been consistently expanding, primarily driven by the increased demand in the healthcare industry for its antibacterial and disinfection properties, as well as its conductivity applications in electronics. With the continual maturation of nanotechnology and the exploration of new application domains, the nano silver powdernano silver powder market is poised for sustained growth. In the future, as environmental consciousness rises, the potential of nano silver powder to replace traditional materials is likely to be further tapped into, projecting broader market prospects in emerging fields.
Report Scope
This report, based on historical analysis (2018-2022) and forecast calculation (2023-2029), aims to help readers to get a comprehensive understanding of global Nano Silver Powder market with multiple angles, which provides sufficient supports to readers’ strategy and decision making.
Having extensive expertise as a consultant and industry specialist in Nano Silver Powder manufacturing and design, it is evident that this sector has witnessed remarkable growth in recent times. Nano Silver Powders have evolved beyond their primary purpose of noise reduction and have become integral to the performance and visual appeal of modern motorcycles.
In-depth market research indicates that the expansion of the Nano Silver Powder market can be attributed to several key factors. Firstly, there is a growing demand for high-performance motorcycles, which has propelled the need for advanced Nano Silver Powders. Additionally, customization has become increasingly popular among motorcycle enthusiasts, driving the market further. Furthermore, stringent emission regulations imposed on motorcycles have necessitated the development and utilization of Nano Silver Powders to meet compliance requirements. Moreover, the continuous advancements in technology and materials used in the manufacturing process of Nano Silver Powder have significantly boosted their demand.
The current Nano Silver Powder market offers a wide range of products customized to different products and user preferences. The surging popularity of this industry has further contributed to the market's growth. we can anticipate continued technological advancements and innovative approaches in Nano Silver Powder manufacturing.
Nano Silver Powder Market Forecast by regions, type and application, with sales and revenue, from 2022 to 2032. Nano Silver Powder Market Share, distributors, major suppliers, changing price patterns and the supply chain of raw materials is highlighted in the report.Nano Silver Powder Market Size report provides important information regarding the total valuation that this industry holds presently and it also lists the segmentation of the market along with the growth opportunities present across this business vertical.This Report Focuses on the Nano Silver Powder Market manufacturers, to study the sales, value, market share and development plans in the future.
It is Define, describe and forecast the Nano Silver Powder Market Growth by type, application, and region to Study the global and key regions market potential and advantage, opportunity and challenge, restraints and risks. Know significant trends and factors driving or inhibiting the Nano Silver Powder Market growth opportunities in the market for stakeholders by identifying the high growth segments. Strategically it examines each submarket with respect to individual growth trend and their contribution to the Nano Silver Powder Market.
Enquire before purchasing this report - https://www.marketreportsworld.com/enquiry/pre-order-enquiry/26163473
What are the types of Nano Silver Powder available in the Market?
What are the factors driving application of the growth of the Nano Silver Powder Market?
The Global Nano Silver Powder Market Trends, development and marketing channels are analysed. Finally, the feasibility of new investment projects is assessed and overall research conclusions offered.The global Nano Silver Powder Market Growth is anticipated to rise at a considerable rate during the forecast period, between 2021 and 2032. In 2021, the market was growing at a steady rate and with the rising adoption of strategies by key players, the market is expected to rise over the projected horizon.
The Impact of Covid-19 and the Russia-Ukraine War on the Nano Silver Powder Market
The Nano Silver Powder market is anticipated to be significantly influenced by two major factors: The Russia-Ukraine war and the post-Covid-19 pandemic. The ongoing war has created political and economic instability, resulting in a decline in consumer purchasing power within the region. Additionally, the pandemic has severely disrupted supply chains, leading to challenges in production and distribution for manufacturers. As a result, the market is expected to witness sluggish growth due to the combined impact of these factors.
However, it is important to note that Nano Silver Powder are considered essential components, and as the situation stabilizes, there is an expected rebound in demand for these products. In this scenario, major manufacturers with diverse customer bases, the ability to adapt to production fluctuations, and strong financial capabilities are likely to be the primary beneficiaries, as they can navigate through prolonged periods of uncertainty.
The Nano Silver Powder plays a vital role in the industry. Its usage in North America, Europe, the USA, and China is governed by local regulations and vehicle emissions standards. In the Asia-Pacific (APAC) region, the specific usage of Nano Silver Powder varies based on individual country regulations.
Which regions are leading the Nano Silver Powder Market?
Nano Silver Powder Market Outlook (2024 - 2032)
From 2024 to 2032, the Nano Silver Powder market displays a consistent and positive growth direction, indicating a favorable outlook for the industry. This growth is propelled by several key factors, including increasing consumer demand, advancements in technology, and shifting consumer preferences.
A significant driver of the Nano Silver Powder market is the growing consumer awareness of health and wellness. This heightened consciousness has resulted in a surge in demand for Nano Silver Powder products that are perceived as healthier and more natural alternatives. Furthermore, technological advancements within the Nano Silver Powder industry have led to the emergence of more efficient and sustainable production methods, further enhancing market growth.
Furthermore, key players in the industry are making substantial investments, which are anticipated to drive innovation and fuel market expansion. These investments primarily focus on the development of new products and the expansion of distribution networks, which in turn will stimulate future demand.
In summary, the outlook for the Nano Silver Powder market is optimistic, with sustained growth expected in the coming years. Increasing consumer demand, advancements in technology, and investments from key industry players are poised to drive growth and advance innovation within the market.
Nano Silver Powder Market Report Acknowledges:
Purchase this report (Price 2900 USD for a single-user license) - https://www.marketreportsworld.com/purchase/26163473
What is the current market size of the Nano Silver Powder market?
Detailed TOC of Global Nano Silver Powder Market Research Report, 2024-2032
1 Nano Silver Powder Market Overview
2 Nano Silver Powder Market Upstream and Downstream Analysis
3 Players Profiles
5 Global Nano Silver Powder Sales, Revenue, Price Trend by Type
6 Global Nano Silver Powder Market Analysis by Application
7 Global Nano Silver Powder Sales and Revenue Region Wise (2017-2022)
8 Global Nano Silver Powder Market Forecast (2022-2032)
9 Industry Outlook
10 Research Findings and Conclusion
11 Appendix
Continued...
Get a sample PDF of the report -https://www.marketreportsworld.com/enquiry/request-sample/26163473
About Us: –
Market Reports World is the Credible Source for Gaining the Market Reports that will Provide you with the Lead Your Business Needs. Market is changing rapidly with the ongoing expansion of the industry. Advancement in the technology has provided today’s businesses with multifaceted advantages resulting in daily economic shifts. Thus, it is very important for a company to comprehend the patterns of the market movements in order to strategize better. An efficient strategy offers the companies with a head start in planning and an edge over the competitors.
On the other hand, it was also demonstrated that AgNO3 and metal-based nanoparticles (AgNPs) had strong potential for cytotoxic, antiproliferative, and apoptotic property in H-ras 5RP7 cells and cervical cancer, respectively.284,285
Biosynthesized nanosilver from the extract of Pterocladiella capillacea (11.4±3.52 nm) and P. aeruginosa (13–76 nm) showed great potential against human hepatocellular carcinoma (HepG2) cell lines and human cervical cancer cells (HeLa), respectively.286,287 In another study, it was found that green-synthesized nanosilver (45±0.15 nm) from novel Nocardiopsis spp. had potent activity against in vitro human cervical cancer cell line. The IC50 value was recorded in the range of 200 μg/mL of AgNPs against HeLa cancer cells.288 It was also found that the plumbagin-caged nanosilver induced ~80% cell death at a concentration of 2.5 μM, whereas no cytotoxicity was observed for normal cells.289
A study published by Yeasmin et al demonstrated that AgNPs with controlled shape are more effective against many types of cancer cell lines. They stabilized the shape of spherical silver nanoparticles by interaction with natural gum and then screened against cervical cancer cell lines (HeLa), lung cancer (A549), and mice macrophage or RAW 264.7 and found that the particles effectively killed these cell lines in a dose-dependent manner.290 Venil et al reported flexirubin (a bacterial pigment)-mediated silver nanoparticles for the first time that were highly cytotoxic (IC50 value of 36 μg/mL) against human breast cancer cell lines (MCF-7).291
Nowadays, chitosan-based biosynthesized silver nanoparticles are mostly synthesized and used against different cancer cell lines. A study performed by Venkatesan et al demonstrated that porous chitosan-alginate-biosynthesized AgNPs exhibited cytotoxic effects against breast cancer cell line MDA-MB-231 (IC50 =4.6 mg).292 A recent study demonstrated that loaded quinazolinone polypyrrole/chitosan silver chloride NC had active anticancer efficacy against Ehrlich ascites carcinoma cells.293 The chitosan-silver hybrid nanoparticles were proven to induce apoptosis in HepG2 cells by downregulating BCL2 gene and upregulating P53.294
AgNPs have received enormous attention for their bactericidal potential, while the antiviral activities of metal nanoparticles remain an emergent area. The potential of AgNPs was studied in both prokaryotic and eukaryotic organisms,295 and it was reported that small-sized AgNPs of around 25 nm or less had outstanding potential in viral infection inhibition.296 The aqueous extract of Ricinus communis was used for the synthesis of nanoparticles, which resulted in AgNPs sized 1,000 nm. Smaller-sized (5–20 nm) AgNPs were obtained from fungi. The results indicated that the small-sized AgNPs had an excellent ability to decrease the infection potential of herpes simplex virus types (HSV) 1/2 and human parainfluenza virus type 3.297
Baram-Pinto et al investigated the inhibitory effect of AgNPs against HSV-1 and demonstrated that sulfonate-capped nanosilver inhibited HSV-1 infection. Furthermore, they demonstrated that AgNPs prevented the attachment and entry of virus into a cell or prevented the cell from spreading the virus. The heparan sulfate is a cellular primary acceptor of HSV, and thus competes with the virus for attaching to the cell and the potential was enhanced due to the presence of the inner core AgNPs.298 This study also demonstrated the virucidal action of AgNPs. These nanoparticles exhibited anti-HIV activity at an early stage of viral infection and also prevented the further replication of HIV-1.299 Furthermore, the viruses and other microbial strains were grown under multicycler growth condition in the absence or presence of colloidal silver to check the antimicrobial property. As expected, no viral growth was seen with any strains tested.300
A recent study also showed that T lymphocyte (T)-tropic and macrophage (M)-tropic strains of HIV-1 were extremely susceptible to the AgNPs coated with polyurethane condom.15
In a recent study, different types of nanosilver particles were biosynthesized from F. oxysporum (4–13 nm), Curvularia spp. (5–23 nm), and Alternaria and Phoma spp. (7–20 nm). Silver particles produced from F. oxysporum and Curvularia spp. had exceptional antiviral activity but were less cytotoxic to Vero cells, whereas particles produced from Alternaria and Phoma spp. showed moderate virucidal action. This study also confirmed that small-sized nanoparticles have excellent ability to inhibit the replication of virus as compared to larger ones.297
More recently, the tannic acid-modified AgNPs in the range of 13, 33, and 46 nm were found to reduce HSV-2 infectivity in vivo and in vitro. In particular, tannic acid in the same amount also showed somewhat in vivo potential against the virus. Therefore, tannic acid-modified nanosilver was used as an antimicrobial agent in addition to cream or protective gel used for oral herpes infections treatment.301
According to the WHO, leishmaniasis is the sixth most infectious disease.302 Leishmaniasis is one of the most abandoned tropical infections around the globe, with occurrence in 88 countries and a predictable number of 500,000 cases of visceral form and 1.5 million cases of cutaneous leishmaniasis.303 Rossi-Bergmann et al demonstrated the potential function of biosynthesized AgNPs (using F. oxysporum) against Leishmania amazonensis promastigotes both in vivo and in vitro. They also compared the biologically and chemically synthesized AgNPs. Their results demonstrated that biosynthesized nanosilver was four times more active as compared to chemically produced AgNPs in vitro, while the in vivo results showed it was even more effective.304
The protozoal vector-borne diseases are the most common and important infections in developed regions, resulting in over one million deaths from malaria on yearly bases, worldwide.305 To control the malaria vector, researchers strive to discover innovative approach against antimalarial agents. Among various antimalarial drugs, AgNPs have also been evaluated against malarial parasites and reported with promising potential against malaria. In recent studies, the biologically synthesized AgNPs from Andrographis paniculata Nees. (Acanthaceae) ~55 nm in size306 and Catharanthus roseus leaves (approximate size 35–55 nm) were tested against P. falciparum.307 In another study, the higher antimalarial potential of AgNPs was reported. The AgNPs were bio-reduced in 5% Cassia occidentalis leaf broth against chloroquine-sensitive and chloroquine-resistant strains of P. falciparum and malarial vector Anopheles stephensi.232
The global "Nano Silver Powder Market" report indicates a |Consistent Growth of 2024| pattern in recent times, which is expected to continue positively until 2032. A prominent trend in the Nano Silver Powder market is the increasing demand for products that are environmentally sustainable and eco-friendly. Another significant observation in this market is the rising incorporation of technology to elevate both the quality and efficiency of products. State-of-the-art technologies such as artificial intelligence, machine learning, and blockchain are being harnessed to create innovative products that surpass conventional options in terms of both effectiveness and efficiency. The Nano Silver Powder Market Research Report for 2024 highlights trends, growth prospects, and potential scenarios up to the year 2032.
The Nano Silver Powder market provides detailed insights into the five major elements (size, share, scope, growth and potential of the industry). It offers valuable information to help businesses identify opportunities and potential risks within the market. This detailed report is spread across 105 pages, ensuring an in-depth analysis of the subject matter.
Overall, the Nano Silver Powder market is poised for continued expansion in the coming years due to the increasing demand for sustainable and innovative products, as well as the widespread adoption of technology. By 2032, the global Nano Silver Powder market size is projected to reach multimillion figures, displaying an unexpected compound annual growth rate between 2024 and 2032 when compared to the figures observed in 2021.
Companies Covered: Nano Silver Powder Market Ask for A Sample Report
These companies have the potential to drive market growth through various strategies. They can focus on offering innovative and high-performance products, taking advantage of advancements in technology. Additionally, expanding their distribution channels to target new customers would be beneficial. Strategic partnerships and collaborations can also be pursued to strengthen market presence and enhance competitiveness.
Who is the largest manufacturers of Nano Silver Powder Market worldwide?
The global Nano Silver Powder market size is segmented on the basis of application, end user, and region, with focus on manufacturers in different regions. The study has detailed the analysis of different factors that increase the industries growth. This study also provides the scope of different segments and applications that can potentially influence the industry in the future. Pricing analysis is covered in this report according to each type, manufacturer, regional analysis, price. Nano Silver Powder Market Share report provides overview of market value structure, cost drivers, various driving factors and analyze industry atmosphere, then studies global outline of industry size, demand, application, revenue, product, region and segments.
What is Nano Silver Powder?
Nano Silver Powder is a kind of ultra-fine nano-silver particles powder , prepared through special production process. It has a wide range of applications with its excellent performance. It can be used for sterilization, can also be used as a catalyst, etc.
According to 2024 New survey, global Nano Silver Powder market is projected to reach USD 46 million in 2029, increasing from USD 32 million in 2022, with the CAGR of 5.3% during the period of 2023 to 2029. Influencing issues, such as economy environments, COVID-19 and Russia-Ukraine War, have led to great market fluctuations in the past few years and are considered comprehensively in the whole Nano Silver Powder market research.
Nano silver powder is a promising novel material with widespread applications, making significant strides in sectors such as healthcare, electronics, and environmental protection. The market has been consistently expanding, primarily driven by the increased demand in the healthcare industry for its antibacterial and disinfection properties, as well as its conductivity applications in electronics. With the continual maturation of nanotechnology and the exploration of new application domains, the nano silver powder market is poised for sustained growth. In the future, as environmental consciousness rises, the potential of nano silver powder to replace traditional materials is likely to be further tapped into, projecting broader market prospects in emerging fields.
Report Scope
This report, based on historical analysis (2018-2022) and forecast calculation (2023-2029), aims to help readers to get a comprehensive understanding of global Nano Silver Powder market with multiple angles, which provides sufficient supports to readers’ strategy and decision making.
Having extensive expertise as a consultant and industry specialist in Nano Silver Powder manufacturing and design, it is evident that this sector has witnessed remarkable growth in recent times. Nano Silver Powders have evolved beyond their primary purpose of noise reduction and have become integral to the performance and visual appeal of modern motorcycles.
In-depth market research indicates that the expansion of the Nano Silver Powder market can be attributed to several key factors. Firstly, there is a growing demand for high-performance motorcycles, which has propelled the need for advanced Nano Silver Powders. Additionally, customization has become increasingly popular among motorcycle enthusiasts, driving the market further. Furthermore, stringent emission regulations imposed on motorcycles have necessitated the development and utilization of Nano Silver Powders to meet compliance requirements. Moreover, the continuous advancements in technology and materials used in the manufacturing process of Nano Silver Powder have significantly boosted their demand.
The current Nano Silver Powder market offers a wide range of products customized to different products and user preferences. The surging popularity of this industry has further contributed to the market's growth. we can anticipate continued technological advancements and innovative approaches in Nano Silver Powder manufacturing.
Nano Silver Powder Market Forecast by regions, type and application, with sales and revenue, from 2022 to 2032. Nano Silver Powder Market Share, distributors, major suppliers, changing price patterns and the supply chain of raw materials is highlighted in the report.Nano Silver Powder Market Size report provides important information regarding the total valuation that this industry holds presently and it also lists the segmentation of the market along with the growth opportunities present across this business vertical.This Report Focuses on the Nano Silver Powder Market manufacturers, to study the sales, value, market share and development plans in the future.
It is Define, describe and forecast the Nano Silver Powder Market Growth by type, application, and region to Study the global and key regions market potential and advantage, opportunity and challenge, restraints and risks. Know significant trends and factors driving or inhibiting the Nano Silver Powder Market growth opportunities in the market for stakeholders by identifying the high growth segments. Strategically it examines each submarket with respect to individual growth trend and their contribution to the Nano Silver Powder Market.
Enquire before purchasing this report - https://www.marketreportsworld.com/enquiry/pre-order-enquiry/26163473
What are the types of Nano Silver Powder available in the Market?
What are the factors driving application of the growth of the Nano Silver Powder Market?
The Global Nano Silver Powder Market Trends, development and marketing channels are analysed. Finally, the feasibility of new investment projects is assessed and overall research conclusions offered.The global Nano Silver Powder Market Growth is anticipated to rise at a considerable rate during the forecast period, between 2021 and 2032. In 2021, the market was growing at a steady rate and with the rising adoption of strategies by key players, the market is expected to rise over the projected horizon.
The Impact of Covid-19 and the Russia-Ukraine War on the Nano Silver Powder Market
The Nano Silver Powder market is anticipated to be significantly influenced by two major factors: The Russia-Ukraine war and the post-Covid-19 pandemic. The ongoing war has created political and economic instability, resulting in a decline in consumer purchasing power within the region. Additionally, the pandemic has severely disrupted supply chains, leading to challenges in production and distribution for manufacturers. As a result, the market is expected to witness sluggish growth due to the combined impact of these factors.
However, it is important to note that Nano Silver Powder are considered essential components, and as the situation stabilizes, there is an expected rebound in demand for these products. In this scenario, major manufacturers with diverse customer bases, the ability to adapt to production fluctuations, and strong financial capabilities are likely to be the primary beneficiaries, as they can navigate through prolonged periods of uncertainty.
The Nano Silver Powder plays a vital role in the industry. Its usage in North America, Europe, the USA, and China is governed by local regulations and vehicle emissions standards. In the Asia-Pacific (APAC) region, the specific usage of Nano Silver Powder varies based on individual country regulations.
Which regions are leading the Nano Silver Powder Market?
Nano Silver Powder Market Outlook (2024 - 2032)
From 2024 to 2032, the Nano Silver Powder market displays a consistent and positive growth direction, indicating a favorable outlook for the industry. This growth is propelled by several key factors, including increasing consumer demand, advancements in technology, and shifting consumer preferences.
A significant driver of the Nano Silver Powder market is the growing consumer awareness of health and wellness. This heightened consciousness has resulted in a surge in demand for Nano Silver Powder products that are perceived as healthier and more natural alternatives. Furthermore, technological advancements within the Nano Silver Powder industry have led to the emergence of more efficient and sustainable production methods, further enhancing market growth.
Furthermore, key players in the industry are making substantial investments, which are anticipated to drive innovation and fuel market expansion. These investments primarily focus on the development of new products and the expansion of distribution networks, which in turn will stimulate future demand.
In summary, the outlook for the Nano Silver Powder market is optimistic, with sustained growth expected in the coming years. Increasing consumer demand, advancements in technology, and investments from key industry players are poised to drive growth and advance innovation within the market.
Nano Silver Powder Market Report Acknowledges:
Purchase this report (Price 2900 USD for a single-user license) - https://www.marketreportsworld.com/purchase/26163473
What is the current market size of the Nano Silver Powder market?
Detailed TOC of Global Nano Silver Powder Market Research Report, 2024-2032
1 Nano Silver Powder Market Overview
2 Nano Silver Powder Market Upstream and Downstream Analysis
3 Players Profiles
5 Global Nano Silver Powder Sales, Revenue, Price Trend by Type
6 Global Nano Silver Powder Market Analysis by Application
7 Global Nano Silver Powder Sales and Revenue Region Wise (2017-2022)
8 Global Nano Silver Powder Market Forecast (2022-2032)
9 Industry Outlook
10 Research Findings and Conclusion
11 Appendix
Continued...
Get a sample PDF of the report -https://www.marketreportsworld.com/enquiry/request-sample/26163473
About Us: –
Market Reports World is the Credible Source for Gaining the Market Reports that will Provide you with the Lead Your Business Needs. Market is changing rapidly with the ongoing expansion of the industry. Advancement in the technology has provided today’s businesses with multifaceted advantages resulting in daily economic shifts. Thus, it is very important for a company to comprehend the patterns of the market movements in order to strategize better. An efficient strategy offers the companies with a head start in planning and an edge over the competitors.
Want more information on silver nano antibacterial powder? Feel free to contact us.