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International Nano Letters

, 2:32 | Cite as

Silver nanoparticles: mechanism of antimicrobial action, synthesis, medical applications, and toxicity effects

  • Sukumaran Prabhu
  • Eldho K Poulose
Open Access
Review

Abstract

Silver nanoparticles are nanoparticles of silver which are in the range of 1 and 100 nm in size. Silver nanoparticles have unique properties which help in molecular diagnostics, in therapies, as well as in devices that are used in several medical procedures. The major methods used for silver nanoparticle synthesis are the physical and chemical methods. The problem with the chemical and physical methods is that the synthesis is expensive and can also have toxic substances absorbed onto them. To overcome this, the biological method provides a feasible alternative. The major biological systems involved in this are bacteria, fungi, and plant extracts. The major applications of silver nanoparticles in the medical field include diagnostic applications and therapeutic applications. In most of the therapeutic applications, it is the antimicrobial property that is being majorly explored, though the anti-inflammatory property has its fair share of applications. Though silver nanoparticles are rampantly used in many medical procedures and devices as well as in various biological fields, they have their drawbacks due to nanotoxicity. This review provides a comprehensive view on the mechanism of action, production, applications in the medical field, and the health and environmental concerns that are allegedly caused due to these nanoparticles. The focus is on effective and efficient synthesis of silver nanoparticles while exploring their various prospective applications besides trying to understand the current scenario in the debates on the toxicity concerns these nanoparticles pose.

Keywords

Silver nanoparticle Antimicrobial action Synthesis Medical applications Silver nanotoxicity 

Review

Introduction

The medical properties of silver have been known for over 2,000 years. Since the nineteenth century, silver-based compounds have been used in many antimicrobial applications. Nanoparticles have been known to be used for numerous physical, biological, and pharmaceutical applications. Silver nanoparticles are being used as antimicrobial agents in many public places such as railway stations and elevators in China, and they are said to show good antimicrobial action.

It is a well-known fact that silver ions and silver-based compounds are highly toxic to microorganisms which include 16 major species of bacteria[1, 2]. This aspect of silver makes it an excellent choice for multiple roles in the medical field. Silver is generally used in the nitrate form to induce antimicrobial effect, but when silver nanoparticles are used, there is a huge increase in the surface area available for the microbe to be exposed to. Though silver nanoparticles find use in many antibacterial applications, the action of this metal on microbes is not fully known. It has been hypothesized that silver nanoparticles can cause cell lysis or inhibit cell transduction. There are various mechanisms involved in cell lysis and growth inhibition.

There are many ways depicted in various literatures to synthesize silver nanoparticles. These include physical, chemical, and biological methods. The physical and chemical methods are numerous in number, and many of these methods are expensive or use toxic substances which are major factors that make them ‘not so favored’ methods of synthesis. An alternate, feasible method to synthesize silver nanoparticles is to employ biological methods of using microbes and plants.

Silver nanoparticles find use in many fields, and the major applications include their use as catalysts, as optical sensors of zeptomole (10−21) concentration, in textile engineering, in electronics, in optics, and most importantly in the medical field as a bactericidal and as a therapeutic agent. Silver ions are used in the formulation of dental resin composites; in coatings of medical devices; as a bactericidal coating in water filters; as an antimicrobial agent in air sanitizer sprays, pillows, respirators, socks, wet wipes, detergents, soaps, shampoos, toothpastes, washing machines, and many other consumer products; as bone cement; and in many wound dressings to name a few. Though there are various benefits of silver nanoparticles, there is also the problem of nanotoxicity of silver. There are various literatures that suggest that the nanoparticles can cause various environmental and health problems, though there is a need for more studies to be conducted to conclude that there is a real problem with silver nanoparticles.

This review provides an idea of the antimicrobial properties silver possesses as a nanoparticle, the various methods employed to synthesize silver nanoparticles, and an overview of their applications in the medical field and also discusses the toxicity of silver nanoparticles. The focus is on the characteristics of silver nanoparticles which make them excellent candidates for use in the medical field besides delving into the unique ability of certain biological systems to synthesize silver nanoparticles and also looks at the chances of these particles to induce toxicity in humans and the environment as a whole.

Action of silver nanoparticles on microbes

The exact mechanism which silver nanoparticles employ to cause antimicrobial effect is not clearly known and is a debated topic. There are however various theories on the action of silver nanoparticles on microbes to cause the microbicidal effect.

Silver nanoparticles have the ability to anchor to the bacterial cell wall and subsequently penetrate it, thereby causing structural changes in the cell membrane like the permeability of the cell membrane and death of the cell. There is formation of ‘pits’ on the cell surface, and there is accumulation of the nanoparticles on the cell surface[3]. The formation of free radicals by the silver nanoparticles may be considered to be another mechanism by which the cells die. There have been electron spin resonance spectroscopy studies that suggested that there is formation of free radicals by the silver nanoparticles when in contact with the bacteria, and these free radicals have the ability to damage the cell membrane and make it porous which can ultimately lead to cell death[4, 5].

It has also been proposed that there can be release of silver ions by the nanoparticles[6], and these ions can interact with the thiol groups of many vital enzymes and inactivate them[7]. The bacterial cells in contact with silver take in silver ions, which inhibit several functions in the cell and damage the cells. Then, there is the generation of reactive oxygen species, which are produced possibly through the inhibition of a respiratory enzyme by silver ions and attack the cell itself. Silver is a soft acid, and there is a natural tendency of an acid to react with a base, in this case, a soft acid to react with a soft base[8]. The cells are majorly made up of sulfur and phosphorus which are soft bases. The action of these nanoparticles on the cell can cause the reaction to take place and subsequently lead to cell death. Another fact is that the DNA has sulfur and phosphorus as its major components; the nanoparticles can act on these soft bases and destroy the DNA which would definitely lead to cell death[9]. The interaction of the silver nanoparticles with the sulfur and phosphorus of the DNA can lead to problems in the DNA replication of the bacteria and thus terminate the microbes.

It has also been found that the nanoparticles can modulate the signal transduction in bacteria. It is a well-established fact that phosphorylation of protein substrates in bacteria influences bacterial signal transduction. Dephosphorylation is noted only in the tyrosine residues of gram-negative bacteria. The phosphotyrosine profile of bacterial peptides is altered by the nanoparticles. It was found that the nanoparticles dephosphorylate the peptide substrates on tyrosine residues, which leads to signal transduction inhibition and thus the stoppage of growth. It is however necessary to understand that further research is required on the topic to thoroughly establish the claims[10] (Figure1).
Figure 1

Various modes of action of silver nanoparticles on bacteria.

Chemical and physical syntheses of silver nanoparticles

The production of nanoparticles majorly involves physical and chemical processes. Silver nanomaterials can be obtained by both the so-called ‘top-down’ and ‘bottom-up’ methods. The top-down method involves the mechanical grinding of bulk metals and subsequent stabilization of the resulting nanosized metal particles by the addition of colloidal protecting agents[11, 12]. The bottom-up methods, on the other hand, include reduction of metals, electrochemical methods, and sonodecomposition.

There are various physical and chemical methods, of which the simplest method involves the chemical method of reduction of the metal salt AgBF4 by NaBH4 in water. The obtained nanoparticles with the size range of 3 to 40 nm are characterized by transmission electron microscopy (TEM) and UV-visible (UV–vis) absorption spectroscopy to evaluate their quality[13]. There is the electrochemical method which involves the electroreduction of AgNO3 in aqueous solution in the presence of polyethylene glycol. The nanoparticles thus produced are characterized by TEM, X-ray diffraction, and UV–vis absorption spectroscopy and are 10 nm in diameter[14].

Sonodecomposition, to yield silver nanoparticles, involves the usage of ultrasonic waves to induce cavitation, a phenomenon whereby the passage of ultrasonic waves through an aqueous solution yields microscopic bubbles that expand and ultimately burst. The synthesis of silver nanoparticles involves sonochemical reduction of an aqueous silver nitrate solution in an atmosphere of argon-hydrogen. The silver nanoparticles are then characterized by TEM, X-ray diffraction, absorption spectroscopy, differential scanning calorimetry, and EPR spectroscopy and are found to be 20 nm in diameter. The mechanism of the sonochemical reduction occurs due to the generation of hydrogen radicals during the sonication process[15].

Nanoparticles are also synthesized within aqueous foams as a template. The method involves electrostatically complexing silver ions with an anionic surfactant aerosol in highly stable liquid foam. The foam is subsequently drained off and reduced by introducing sodium borohydride. These silver nanoparticles are extremely stable in solution, suggesting that the aerosol stabilizes them. This method gave nanoparticles of 5 to 40 nm in diameter[16].

A microwave synthesis of silver nanoparticles involves the reduction of silver nanoparticles using variable frequency microwave radiation as against the conventional heating method. The method yields a faster reaction and gives a higher concentration of silver nanoparticles with the same temperature and exposure. It was also found that the higher the concentration of silver nitrate used, the longer the reaction time was and the higher the temperature, the bigger the particle size was, while the higher the poly(N-vinylpyrrolidone) concentration, the smaller the silver particle size was (between 15 and 25 nm)[17].

There are also many more techniques of synthesizing silver nanoparticles, such as thermal decomposition in organic solvents[18], chemical and photoreduction in reverse micelles[19, 20], spark discharge[21], and cryochemical synthesis[22] which yielded nanoparticles between the ranges of 5 to 80 nm in diameter.

Biological synthesis of silver nanoparticles

The problem with most of the chemical and physical methods of nanosilver production is that they are extremely expensive and also involve the use of toxic, hazardous chemicals, which may pose potential environmental and biological risks. It is an unavoidable fact that the silver nanoparticles synthesized have to be handled by humans and must be available at cheaper rates for their effective utilization; thus, there is a need for an environmentally and economically feasible way to synthesize these nanoparticles. The quest for such a method has led to the need for biomimetic production of silver nanoparticles whereby biological methods are used to synthesize the silver nanoparticles. The growing need to develop environmentally friendly and economically feasible technologies for material synthesis led to the search for biomimetic methods of synthesis[23]. In most cases, the chemical synthesis methods lead to some chemically toxic substances being absorbed on the surface and can hinder their usage in medical applications[24]. There are three major sources of synthesizing silver nanoparticles: bacteria, fungi, and plant extracts. Biosynthesis of silver nanoparticles is a bottom-up approach that mostly involves reduction/oxidation reactions. It is majorly the microbial enzymes or the plant phytochemicals with antioxidant or reducing properties that act on the respective compounds and give the desired nanoparticles. The three major components involved in the preparation of nanoparticles using biological methods are the solvent medium for synthesis, the environmentally friendly reducing agent, and a nontoxic stabilizing agent.

Silver-synthesizing bacteria

The first evidence of bacteria synthesizing silver nanoparticles was established using the Pseudomonas stutzeri AG259 strain that was isolated from silver mine[25]. There are some microorganisms that can survive metal ion concentrations and can also grow under those conditions, and this phenomenon is due to their resistance to that metal. The mechanisms involved in the resistance are efflux systems, alteration of solubility and toxicity via reduction or oxidation, biosorption, bioaccumulation, extracellular complex formation or precipitation of metals, and lack of specific metal transport systems[26]. There is also another aspect that though these organisms can grow at lower concentrations, their exposure to higher concentrations of metal ions can induce toxicity.

The most widely accepted mechanism of silver biosynthesis is the presence of the nitrate reductase enzyme. The enzyme converts nitrate into nitrite. In in vitro synthesis of silver using bacteria, the presence of alpha-nicotinamide adenine dinucleotide phosphate reduced form (NADPH)-dependent nitrate reductase would remove the downstream processing step that is required in other cases. During the reduction, nitrate is converted into nitrite and the electron is transferred to the silver ion; hence, the silver ion is reduced to silver (Ag+ to Ag0). This has been said to be observed in Bacillus licheniformis which is known to secrete NADPH and NADPH-dependent enzymes like nitrate reductase that effectively converts Ag+ to Ag0[27]. The mechanism was further confirmed by using purified nitrate reductase from Fusarium oxysporum and silver nitrate along with NADPH in a test tube, and the change in the color of the reaction mixture to brown and further analysis confirmed that silver nanoparticles were obtained[28]. There are also cases which indicate that there are other ways to biosynthesize silver nanoparticles without the presence of enzymes. It was found that dried cells of Lactobacillus sp. A09 can reduce silver ions by the interaction of the silver ions with the groups on the microbial cell wall[29] (Table1).
Table 1

Silver-synthesizing bacteria and the synthesized particle size

Serial number

Organism

Particle size (nm)

Reference

1

P. stutzeri AG259

200

[30]

2

Bacillus megaterium

46.9

[31]

3

Plectonema boryanum

1 to 200

[32]

4

Enterobacter cloacae

50 to 100

[33]

5

Escherichia coli

5 to 25

[34]

6

B. licheniformis

50

[35]

7

Lactobacillus fermentum

11.2

[36]

8

Klebsiella pneumonia

50

[37]

9

Proteus mirabilis

10 to 20

[38]

10

Brevibacterium casei

50

[39]

Silver-synthesizing fungi

When in comparison with bacteria, fungi can produce larger amounts of nanoparticles because they can secrete larger amounts of proteins which directly translate to higher productivity of nanoparticles[40]. The mechanism of silver nanoparticle production by fungi is said to follow the following steps: trapping of Ag+ ions at the surface of the fungal cells and the subsequent reduction of the silver ions by the enzymes present in the fungal system[41]. The extracellular enzymes like naphthoquinones and anthraquinones are said to facilitate the reduction. Considering the example of F. oxysporum, it is believed that the NADPH-dependent nitrate reductase and a shuttle quinine extracellular process are responsible for nanoparticle formation[42]. Though the exact mechanism involved in silver nanoparticle production by fungi is not fully deciphered, it is believed that the abovementioned phenomenon is responsible for the process. A major drawback of using microbes to synthesize silver nanoparticles is that it is a very slow process when in comparison with plant extracts. Hence, the use of plant extracts to synthesize silver nanoparticles becomes an option that is feasible (Table2).
Table 2

Silver-synthesizing fungi and the synthesized particle size

Serial number

Organism

Particle size (nm)

Reference

1

Verticillium sp.

25

[43]

2

Phoma sp. 3.2883

70

[44]

3

F. oxysporum

20 to 50

[45]

4

Phanerochaete chrysosporium

100

[46]

5

Aspergillus fumigatus

5 to 25

[47]

6

Aspergillus flavus

7 to 10

[48]

7

Fusarium semitectum

10 to 60

[49]

8

Coriolus versicolor

350 to 600

[50]

9

Fusarium solani

5 to 35

[51]

10

Aspergillus clavatus

10 to 25

[52]

Silver-synthesizing plants

The major advantage of using plant extracts for silver nanoparticle synthesis is that they are easily available, safe, and nontoxic in most cases, have a broad variety of metabolites that can aid in the reduction of silver ions, and are quicker than microbes in the synthesis.

The main mechanism considered for the process is plant-assisted reduction due to phytochemicals. The main phytochemicals involved are terpenoids, flavones, ketones, aldehydes, amides, and carboxylic acids. Flavones, organic acids, and quinones are water-soluble phytochemicals that are responsible for the immediate reduction of the ions. Studies have revealed that xerophytes contain emodin, an anthraquinone that undergoes tautomerization, leading to the formation of the silver nanoparticles. In the case of mesophytes, it was found that they contain three types of benzoquinones: cyperoquinone, dietchequinone, and remirin. It was suggested that the phytochemicals are involved directly in the reduction of the ions and formation of silver nanoparticles[53]. Though the exact mechanism involved in each plant varies as the phytochemical involved varies, the major mechanism involved is the reduction of the ions (Table3).
Table 3

Silver-synthesizing plants and the synthesized particle size

Serial number

Organism

Particle size (nm)

Reference

1

Medicago sativa

2 to 20

[54]

2

Azadirachta indica

50

[55]

3

Aloe vera

15 to 20

[56]

4

Cinnamomum camphora leaf

55 to 80

[57]

5

Carica papaya fruit

15

[58]

6

Cinnamomum zeylanicum bark

50 to 100

[59]

7

Jatropha curcas

10 to 20

[60]

8

Desmodium triflorum

5 to 20

[61]

9

Coriandrum sativum leaf

26

[62]

10

Piper betle leaf

3 to 37

[63]

Medical applications of silver nanoparticles

Silver nanoparticles, due to their unique properties, find use in many day-to-day applications in human life. A few examples include their addition in house cleaning chemicals, in fabric cleaners, as antireflection coatings, to improve the transfer of heat from collectors of solar energy to their fuel tanks, to produce high-performance delicate electronics, and in hundreds of other applications. Though all these are important applications of silver nanoparticles, perhaps their need is most desired in the medical field.

The general aspect of nanoparticles is that the small size of nanoparticles provides for a larger surface area for the particle and hence increases the effect. The nanosize of the particles also increases the penetration potential of the silver particles, hence again aiding in better utilization of the metal properties. Based on the size factor alone, nanoparticles have the ability to penetrate the circulatory system and translocate even the blood–brain barrier in the human system.

The antimicrobial nature of silver nanoparticles is the most exploited nature of silver nanoparticles in the medical field, though the anti-inflammatory nature is also considered immensely useful in the medical field. Initial studies have suggested that the acceleration of wound healing in the presence of nanoparticles is due to the reduction of local matrix metalloproteinase (MMP) activity and the increase in neutrophil apoptosis within the wound. It has been suggested that the MMP can induce inflammation and hence cause non-healing wounds[64]. A reduction in the levels of pro-inflammatory cytokines was also demonstrated in a mouse model with burn injury when silver nanoparticles were introduced[65]. It was also found that silver nanoparticles can inhibit the activities of interferon gamma and tumor necrosis factor alpha which are involved in inflammation[66]. Though these studies prove that silver nanoparticles are involved in the anti-inflammatory effects, the exact, precise mechanism of action remains to be determined. The anti-inflammatory effects induced by nanosilver however make it an excellent candidate for use as anti-inflammatory agents that can be used for various therapies.

Dr. Robert Burrell is said to have developed the world's first nanosilver-based wound dressing in 1995. He developed Acticoat that speeds up the healing process and removes scars if any[67]. Acticoat has become the final word when it comes to wound dressings; however, there are numerous other players in the same field. It is sold worldwide by Smith & Nephew plc. Nanosilver is effective due to the fact that it has a much better effect on the bacteria that tend to infect the wound and due to the fact that it can easily penetrate the wound through the body fluids. The most prominent players in silver-based wound healing are Acticoat 7, Acticoat Moisture Control, Acticoat Absorbent, Silvercel, Aquacel Ag, Contreet F, Urgotol SSD, and Actisorb.

In July 2010, there were reports that scientists at the University of Bath and the burns team of the South West UK Paediatric Burns Centre at Frenchay Hospital in Bristol were working on an advanced bandage that works by releasing antibiotics from nanocapsules triggered by the presence of pathogenic bacteria. The dressing is said to have the potential to change color when the antibiotic is released and hence alerting that there is an infection in the wound. Experts believe that this dressing has great potential in treating burn victims who are susceptible to toxic shock syndrome. With the advent of such system, there can be a reduction in antibiotic resistance[68]. As of 2012, reports suggest that the bandage could be commercialized any time soon. There are newer, efficient, and safer silver nanoparticle-based wound dressings that are being introduced in the market.

Silver nanoparticles are used in bone cements that are used as artificial joint replacements. Polymethyl methacrylate loaded with nanosilver is being considered as bone cement as the nanosilver can induce antimicrobial activity[69]. Ultrahigh molecular weight polyethylene has been the preferred choice for fabricating inserts for total joint replacement components, but it is susceptible to wear and tear which is a major drawback. To overcome this, silver nanoparticles were added, and the presence of silver nanoparticles drastically reduced the wear and tear of the polymer[70]. The currently used methods to prevent surgical infection include antibiotics and antiseptics. Surgical meshes are used to bridge large wounds and for tissue repairs. Though these meshes are effective, they are susceptible to microbial infections. Silver nanoparticle-coated polypropylene mesh is said to have good antimicrobial activity and can be considered an ideal candidate for surgical meshes[71]. The antimicrobial property of silver nanoparticles is documented, and it has immense potential to be used in disinfectants[72]. It is also believed that most medical treatments such as intravenous catheters, endotracheal tubes, wound dressings, bone cements, and dental fillings can all make use of nanosilver to prevent microbial infections.

Nanosilver also has the capacity to be used in biosensing. The plasmonic properties of nanosilver are dictated by its shape, size, and the dielectric medium that surrounds it. Its properties in the dielectric medium that can be exploited make it an ideal candidate for biosensing. Nanosilver biosensors can effectively biosense a large number of proteins that normal biosensors find hard to detect. This unique advantage that nanosilver has can be utilized for detecting various abnormalities and diseases in the human body including cancer[73].

The plasmonic properties of nanosilver also make it an excellent candidate for bioimaging as they, contrary to commonly used fluorescent dyes, do not undergo photobleaching and can be used to monitor dynamic events over an extended period of time[74]. The plasmonic nature of nanosilver can also be used to destroy unwanted cells. The cells can be conjugated to the target cells and then be used to absorb light and convert it to thermal energy; the thermal energy can lead to thermal ablation of the target cells[75].

Studies over the years have proven that it is difficult to remove silver completely if deposited in the body. Animal and human studies have indicated that nanosilver can be excreted through the hair, urine, and feces majorly[76]. However, the main excretion source is biliary excretion. Once orally administered, silver particles pass through the liver, then into the bile, and is excreted out through feces. In the case of inhalation, the particles enter the lungs and subsequently the blood stream and the other organs and are excreted out through urine or feces. The silver particles can enter the body through the skin too from where they enter the blood stream and are taken to various organs and are finally excreted out through urine or feces.

Toxicity of silver nanoparticles

The unique physical and chemical properties of silver nanoparticles make them excellent candidates for a number of day-to-day activities, and also the antimicrobial and anti-inflammatory properties make them excellent candidates for many purposes in the medical field. However, there are studies and reports that suggest that nanosilver can allegedly cause adverse effects on humans as well as the environment.

It is estimated that tonnes of silver are released into the environment from industrial wastes, and it is believed that the toxicity of silver in the environment is majorly due to free silver ions in the aqueous phase. The adverse effects of these free silver ions on humans and all living beings include permanent bluish-gray discoloration of the skin (argyria) or the eyes (argyrosis), and exposure to soluble silver compounds may produce toxic effects like liver and kidney damage; eye, skin, respiratory, and intestinal tract irritations; and untoward changes in blood cells[77].

Since the beginning of the twenty-first century, nanosilver has been gaining popularity and is now being used in almost every field, most importantly the medical field. However, there have been reports of how nanosilver cannot discriminate between different strains of bacteria and can hence destroy microbes beneficial to the ecology[78]. There are only very few studies conducted to assess the toxicity of nanosilver. In one study, in vitro toxicity assay of silver nanoparticles in rat liver cells has shown that even low-level exposure to silver nanoparticles resulted in oxidative stress and impaired mitochondrial function[79]. Silver nanoparticles also proved to be toxic to in vitro mouse germ line stem cells as they impaired mitochondrial function and caused leakage through the cell membranes. Nanosilver aggregates are said to be more cytotoxic than asbestos[80]. There is evidence that shows that silver ions cause changes in the permeability of the cell membrane to potassium and sodium ions at concentrations that do not even limit sodium, potassium, ATP, or mitochondrial activity[81]. The literature also proves that nanosilver can induce toxic effects on the proliferation and cytokine expression by peripheral blood mononuclear cells[66]. Nanosilver is also known to show severe toxic effects on the male reproductive system. Research shows that nanosilver can cross the blood-testes barrier and be deposited in the testes where they adversely affect the sperm cells[82]. Even commercially available silver-based dressings have been proved to have cytotoxic effects on various experimental models[83]. In vivo studies on the oral toxicity of nanosilver on rats have indicated that the target organ in mouse for the nanosilver was the liver. It was also found from histopathological studies that there was a higher incidence of bile duct hyperplasia, with or without necrosis, fibrosis, and pigmentation in the study animals[84]. Studies have also suggested that there is release of silver when the nanoparticles are stored over a period of time. Hence, it has to be said that aged nanosilver is more toxic than new nanosilver[85].

Nanosilver with its antimicrobial activity can hinder the growth of many ‘friendly’ bacteria in the soil. By showing toxic effects on denitrifying bacteria, silver can disrupt the denitrification process, which involves the conversion of nitrates into nitrogen gas which is essential for the plants. Loss of environmental denitrification through reduction of plant productivity can lead to eutrophication of rivers, lakes, and marine ecosystems and destroy the ecosystem[86]. Nanosilver also has toxic effects on aquatic animals because silver ions can interact with the gills of fish and inhibit basolateral Na+-K+-ATPase activity, which can in turn inhibit osmoregulation in the fish[87]. To understand the toxic potential nanosilver has on the freshwater environment, the Daphnia magna 48-h immobilization test was conducted, and the results showed that the silver nanoparticles have to be classified under ‘category acute 1’ as per the Globally Harmonized System of Classification and Labelling of Chemicals, suggesting that the release of nanosilver into the environment has to be carefully considered[88].

Though these studies tend to suggest that nanosilver can induce toxicity to living beings, it has to be understood that the studies on nanosilver toxicity were done in in vitro conditions which are drastically different from in vivo conditions and at quite high concentrations of nanosilver particles. Hence, it is imperative that more studies be carried out to assess the toxicity effect nanosilver has in vivo before a conclusion on its toxicity is reached.

Conclusions

Silver has always been an excellent antimicrobial and has been used for the purpose for ages. The unique physical and chemical properties of silver nanoparticles only increase the efficacy of silver. Though there are many mechanisms attributed to the antimicrobial activity shown by silver nanoparticles, the actual and most reliable mechanism is not fully understood or cannot be generalized as the nanoparticles are found to act on different organisms in different ways. Chemical and physical methods of silver nanoparticle synthesis were being followed over the decades, but they are found to be expensive and the use of various toxic chemicals for their synthesis makes the biological synthesis the more preferred option. Though bacterial, fungal, and plant extract sources can be used for nanosilver synthesis, the easy availability, the nontoxic nature, the various options available, and the advantage of quicker synthesis make plant extracts the best and an excellent choice for nanosilver synthesis. The uses of silver nanoparticles are varied and many, but the most exploited and desired aspect is their antimicrobial capacity and anti-inflammatory capacity. This has been utilized in various processes in the medical field and has hence been exploited well. However, the downside of silver nanoparticles is that they can induce toxicity at various degrees. It is suggested that higher concentrations of silver nanoparticles are toxic and can cause various health problems. There are also studies that prove that nanoparticles of silver can induce various ecological problems and disturb the ecosystem if released into the environment. Hence, care has to be taken to utilize this marvel well and in a good, effective, and efficient way, understanding its limitations and taking extreme care that it does not cause any harm to an individual or the environment. It can be believed that if utilized properly, silver nanoparticles can be a good friend, but if used haphazardly, they can become a mighty foe. Hence, this current review concludes with a hope and prayer that there would be mechanisms devised to nullify any toxicity caused by nanosilver to humans and the environment so that the unique properties of this substance can be put to great use for human betterment without any controversies.

Notes

Supplementary material

40089_2012_28_MOESM1_ESM.jpeg (74 kb)
Authors’ original file for figure 1

References

  1. 1.
    Slawson RM, Trevors JT, Lee H: Silver accumulation and resistance in Pseudomonas stutzeri. Arch. Microbiol. 1992, 158: 398–404.Google Scholar
  2. 2.
    Zhao GJ, Stevens SE: Multiple parameters for the comprehensive evaluation of the susceptibility of Escherichia coli to the silver ion. Biometals 1998, 11: 27–32. 10.1023/A:1009253223055CrossRefGoogle Scholar
  3. 3.
    Sondi I, Salopek-Sondi B: Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria. J. Colloid Interface Sci. 2004, 275: 177–182. 10.1016/j.jcis.2004.02.012CrossRefGoogle Scholar
  4. 4.
    Danilcauk M, Lund A, Saldo J, Yamada H, Michalik J: Conduction electron spin resonance of small silver particles. Spectrochimaca. Acta. Part A. 2006, 63: 189–191. 10.1016/j.saa.2005.05.002CrossRefGoogle Scholar
  5. 5.
    Kim JS, Kuk E, Yu K, Kim JH, Park SJ, Lee HJ, Kim SH, Park YK, Park YH, Hwang C-Y, Kim YK, Lee YS, Jeong DH, Cho MH: Antimicrobial effects of silver nanoparticles. Nanomedicine 2007, 3: 95–101. 10.1016/j.nano.2006.12.001CrossRefGoogle Scholar
  6. 6.
    Feng QL, Wu J, Chen GQ, Cui FZ, Kim TN, Kim JO: A mechanistic study of the antibacterial effect of silver ions on Escherichia coli and Staphylococcus aureus . J. Biomed. Mater. Res. 2008, 52: 662–668.CrossRefGoogle Scholar
  7. 7.
    Matsumura Y, Yoshikata K, Kunisaki S, Tsuchido T: Mode of bacterial action of silver zeolite and its comparison with that of silver nitrate. Appl. Environ. Microbiol. 2003, 69: 4278–4281. 10.1128/AEM.69.7.4278-4281.2003CrossRefGoogle Scholar
  8. 8.
    Morones JR, Elechiguerra JL, Camacho A, Holt K, Kouri JB, Ramirez JT, Yacaman MJ: The bactericidal effect of silver nanoparticles. Nanotechnology 2005, 16: 2346–2353. 10.1088/0957-4484/16/10/059CrossRefGoogle Scholar
  9. 9.
    Hatchett DW, Henry S: Electrochemistry of sulfur adlayers on low-index faces of silver. J. Phys. Chem. 1996, 100: 9854–9859. 10.1021/jp953757zCrossRefGoogle Scholar
  10. 10.
    Shrivastava S, Bera T, Roy A, Singh G, Ramachandrarao P, Dash D: Characterisation of enhanced antibacterial effects of novel silver nanoparticles. Nanotechnology 2007, 18: 1–9.CrossRefGoogle Scholar
  11. 11.
    Gaffet E, Tachikart M, El Kedim O, Rahouadj R: Nanostructural materials formation by mechanical alloying: morphologic analysis based on transmission and scanning electron microscopic observations. Mater. Charact 1996, 36: 185–190. 10.1016/S1044-5803(96)00047-2CrossRefGoogle Scholar
  12. 12.
    Amulyavichus A, Daugvila A, Davidonis R, Sipavichus C: Study of chemical composition of nanostructural materials prepared by laser cutting of metals. Fizika Met. Met. 1998, 85: 111–117.Google Scholar
  13. 13.
    Thirumalai Arasu V, Prabhu D, Soniya M: Stable silver nanoparticle synthesizing methods and its applications. J. Bio. Sci. Res. 2010, 1: 259–270.Google Scholar
  14. 14.
    Zhu J, Liao X, Chen H-Y: Electrochemical preparation of silver dendrites in the presence of DNA. Mater. Res. Bull. 2001, 36: 1687–1692. 10.1016/S0025-5408(01)00600-6CrossRefGoogle Scholar
  15. 15.
    Salkar RA, Jeevanandam P, Aruna ST, Koltypin Y, Gedanken A: The sonochemical preparation of amorphous silver nanoparticles. J. Mater. Chem. 1999, 9: 1333–1335. 10.1039/a900568dCrossRefGoogle Scholar
  16. 16.
    Mandal S, Arumugam S, Pasricha R, Sastry M: Silver nanoparticles of variable morphology synthesized in aqueous foams as novel templates. Bull. Mater. Sci. 2001, 28: 503–510.CrossRefGoogle Scholar
  17. 17.
    Jiang H, Moon K, Zhang Z, Pothukuchi S, Wong CP: Variable frequency microwave synthesis of silver nanoparticles. J. Nanopart. Res. 2006, 8: 117–124. 10.1007/s11051-005-7522-6CrossRefGoogle Scholar
  18. 18.
    Esumi K, Tano T, Torigue K, Meguro K: Preparation and characterization of bimetallic Pd-Cu colloids by thermal decomposition of their acetate compounds in organic solvents. Chem. Mater. 1990, 2: 564–56. 10.1021/cm00011a019CrossRefGoogle Scholar
  19. 19.
    Pileni MP: Fabrication and physical properties of self-organized silver nanocrystals. Pure Appl. Chem. 2000, 72: 53–65. 10.1351/pac200072010053CrossRefGoogle Scholar
  20. 20.
    Sun YP, Atorngitjawat P, Meziani MJ: Preparation of silver nanoparticles via rapid expansion of water in carbon dioxide microemulsion into reductant solution. Langmuir 2001, 17: 5707–5710. 10.1021/la0103057CrossRefGoogle Scholar
  21. 21.
    Tien DC, Tseng KH, Liao CY, Tsung TT: Colloidal silver fabrication using the spark discharge system and its antimicrobial effect on Staphylococcus aureus . Med. Eng. Phys. 2007, 30: 948–952.CrossRefGoogle Scholar
  22. 22.
    Sergeev MB, Kasaikin AV, Litmanovich AE: Cryochemical synthesis and properties of silver nanoparticle dispersions stabilised by poly(2-dimethylaminoethyl methacrylate). Mendeleev. Commun. 1999, 9: 130–132. 10.1070/MC1999v009n04ABEH001080CrossRefGoogle Scholar
  23. 23.
    Kalishwaralal K, Deepak V, Ramkumarpandian S, Nellaiah H, Sangiliyandi G: Extracellular biosynthesis of silver nanoparticles by the culture supernatant of Bacillus licheniformis. Mater. Lett. 2008, 62: 4411–4413. 10.1016/j.matlet.2008.06.051CrossRefGoogle Scholar
  24. 24.
    Parashar UK, Saxena SP, Srivastava A: Bioinspired synthesis of silver nanoparticles. Dig. J. Nanomat. Biostruct. 2009, 4: 159–166.Google Scholar
  25. 25.
    Haefeli C, Franklin C, Hardy K: Plasmid-determined silver resistance in Pseudomonas stutzeri isolated from a silver mine. J. Bacteriol. 1984, 158: 389–392.Google Scholar
  26. 26.
    Husseiny MI, Aziz MAE, Badr Y, Mahmoud MA: Biosynthesis of gold nanoparticles using Pseudomonas aeruginosa . Spectrochimica. Acta. Part A. 2006, 67: 1003–1006.CrossRefGoogle Scholar
  27. 27.
    Vaidyanathan R, Gopalram S, Kalishwaralal K, Deepak V, Pandian SR, Gurunathan S: Enhanced silver nanoparticle synthesis by optimization of nitrate reductase activity. Colloids Surf. B Biointerfaces 2010, 75: 335–341. 10.1016/j.colsurfb.2009.09.006CrossRefGoogle Scholar
  28. 28.
    Anil Kumar S, Majid KA, Gosavi SW, Kulkarni SK, Pasricha R, Ahmad A, Khan MI: Nitrate reductase mediated synthesis of silver nanoparticles from AgNO3. Biotechnol. Lett. 2007, 29: 439–445. 10.1007/s10529-006-9256-7CrossRefGoogle Scholar
  29. 29.
    Fu JK, Liu Y, Gu P, Tang DL, Lin ZY, Yao BX, Weng S: Spectroscopic characterization on the biosorption and bioreduction of Ag(I) by Lactobacillus sp. A09. Acta. Physico-Chimica. Sinica. 2000, 16: 770–782.Google Scholar
  30. 30.
    Tanja K, Ralph J, Eva O, Claes-Göran G: Silver-based crystalline nanoparticles, microbially fabricated. PNAS 1999, 96: 13611–13614. 10.1073/pnas.96.24.13611CrossRefGoogle Scholar
  31. 31.
    Fu JK, Zhang WD, Liu YY, Lin ZY, Yao BX, Weng SZ, Zeng JL: Characterization of adsorption and reduction of noble metal ions by bacteria. Chem. J. Chin. Univ. 1999, 20: 1452–1454.Google Scholar
  32. 32.
    Lengke FM, Fleet EM, Southam G: Biosynthesis of silver nanoparticles by filamentous cyanobacteria a from a silver(I) nitrate complex. Langmuir 2007, 23: 2694–2699. 10.1021/la0613124CrossRefGoogle Scholar
  33. 33.
    Minaeian S, Shahverdi RA, Nohi SA, Shahverdi RH: Extracellular biosynthesis of silver nanoparticles by some bacteria. J. Sci. I. A. U. 2008,17(66):1–4.Google Scholar
  34. 34.
    El-Shanshoury AER, ElSilk SE, Ebeid ME: Extracellular biosynthesis of silver nanoparticles using Escherichia coli ATCC 8739, Bacillus subtilis ATCC 6633, and Streptococcus thermophilus ESh1 and their antimicrobial activities. ISRN Nanotechnology 2011, 2011: 1–7.CrossRefGoogle Scholar
  35. 35.
    Kalimuthu K, Babu RS, Venkataraman D, Bilal M, Gurunathan S: Biosynthesis of silver nanocrystals by Bacillus licheniformis . Colloids Surf. B Biointerfaces 2008, 65: 150–153. 10.1016/j.colsurfb.2008.02.018CrossRefGoogle Scholar
  36. 36.
    Sintubin L, De Windt W, Dick J, Mast J, van der Ha D, Verstraete W, Boon N: Lactic acid bacteria as reducing and capping agent for the fast and efficient production of silver nanoparticles. Appl. Microbiol. Biotechnol. 2009, 84: 741–749. 10.1007/s00253-009-2032-6CrossRefGoogle Scholar
  37. 37.
    Mokhtari M, Deneshpojouh S, Seyedbagheri S, Atashdehghan R, Abdi K, Sarkar S, Minaian S, Shahverdi RH, Shahverdi RA: Biological synthesis of very small silver nanoparticles by culture supernatant of Klebsiella pneumonia : the effects of visible-light irradiation and the liquid mixing process. Mater. Res. Bull. 2009, 44: 1415–1421. 10.1016/j.materresbull.2008.11.021CrossRefGoogle Scholar
  38. 38.
    Samadi N, Golkaran D, Eslamifar A, Jamalifar H, Fazeli MR, Mohseni FA: Intra/extracellular biosynthesis of silver nanoparticles by an autochthonous strain of Proteus mirabilis isolated from photographic waste. J. Biomed. Nanotechnol. 2009, 5: 247–253. 10.1166/jbn.2009.1029CrossRefGoogle Scholar
  39. 39.
    Kalishwaralal K, Deepak V, Pandiana SBRK, Kottaisamy M, BarathManiKanth S, Kartikeyan B, Gurunathan S: Biosynthesis of silver and gold nanoparticles using Brevibacterium casei . Colloids Surf. B Biointerfaces 2010, 77: 257–262. 10.1016/j.colsurfb.2010.02.007CrossRefGoogle Scholar
  40. 40.
    Mohanpuria P, Rana KN, Yadav SK: Biosynthesis of nanoparticles: technological concepts and future applications. J. Nanopart. Res. 2008, 10: 507–517. 10.1007/s11051-007-9275-xCrossRefGoogle Scholar
  41. 41.
    Mukherjee P, Ahmad A, Mandal D, Senapati S, Sainkar SR, Khan MI, Parischa R, Ajaykumar PV, Alam M, Kumar R, Sastry M: Fungus mediated synthesis of silver nanoparticles and their immobilization in the mycelial matrix: a novel biological approach to nanoparticle synthesis. Nano Lett. 2001, 1: 515–519. 10.1021/nl0155274CrossRefGoogle Scholar
  42. 42.
    Ahmad A, Mukherjee P, Senapati S, Mandal D, Khan MI, Kumar R, Sastry M: Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium oxysporum . Colloids Surf. B Biointerfaces 2003, 28: 313–318. 10.1016/S0927-7765(02)00174-1CrossRefGoogle Scholar
  43. 43.
    Mukherjee P, Ahmad A, Mandal D, Senapati S, Sainkar SR, Khan MI, Ramani R, Parischa R, Ajayakumar PV, Alam M, Sastry M, Kumar R: Bioreduction of AuCl4− ions by the fungus, Verticillium sp. and surface trapping of the gold nanoparticles formed. Angew. Chem. Int. Ed 2001, 40: 3585–3588. 10.1002/1521-3773(20011001)40:19<3585::AID-ANIE3585>3.0.CO;2-KCrossRefGoogle Scholar
  44. 44.
    Chen JC, Lin ZH, Ma XX: Evidence of the production of silver nanoparticles via pretreatment of Phoma sp. 3.2883 with silver nitrate. Lett. Appl. Microbiol. 2003, 37: 105–108. 10.1046/j.1472-765X.2003.01348.xCrossRefGoogle Scholar
  45. 45.
    Duran N, Marcato DP, Alves LO, De Souza G, Esposito E: Mechanical aspect of biosynthesis of silver nanoparticles by several Fusarium oxysporum strains. J. Nanobiotechnology 2005, 3: 8–15. 10.1186/1477-3155-3-8CrossRefGoogle Scholar
  46. 46.
    Vigneshwaran N, Kathe AA, Varadarajan PV, Nachane RP, Balasubramanya RH: Biomimetics of silver nanoparticles by white rot fungus, Phaenerochaete chrysosporium . Colloids Surf. B Biointerfaces 2006, 53: 55–59. 10.1016/j.colsurfb.2006.07.014CrossRefGoogle Scholar
  47. 47.
    Bhainsa CK, D’Souza FS: Extracellular biosynthesis of silver nanoparticles using the fungus Aspergillus funigatus . Colloids Surf. B Biointerfaces 2006, 47: 160–164. 10.1016/j.colsurfb.2005.11.026CrossRefGoogle Scholar
  48. 48.
    Vigneshwaran N, Ashtaputre NM, Varadarajan PV, Nachane RP, Paralikar KM, Balasubramanya RH: Biological synthesis of silver nanoparticles using the fungus Aspergillus flavus . Mater. Lett. 2007, 66: 1413–1418.CrossRefGoogle Scholar
  49. 49.
    Basavaraja S, Balaji SD, Lagashetty A, Rajasabd AH, Venkataraman A: Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium semitectum . Mater. Res. Bull 2008, 43: 1164–1170. 10.1016/j.materresbull.2007.06.020CrossRefGoogle Scholar
  50. 50.
    Sanghi R, Verma P: Biomimetic synthesis and characterisation of protein capped silver nanoparticles. Bioresour. Technol. 2009, 100: 501–504. 10.1016/j.biortech.2008.05.048CrossRefGoogle Scholar
  51. 51.
    Gade A, Ingle A, Bawaskar M, Rai M: Fusarium solani : a novel biological agent for extracellular synthesis of nanoparticles. J. Nanopart. Res. 2009, 11: 2079–2085. 10.1007/s11051-008-9573-yCrossRefGoogle Scholar
  52. 52.
    Verma VC, Kharwar RN, Gange AC: Biosynthesis of antimicrobial silver nanoparticles by the endophytic fungus Aspergillus clavatus . Nanomedicine 2010, 5: 33–40. 10.2217/nnm.09.77CrossRefGoogle Scholar
  53. 53.
    Jha AK, Prasad K, Prasad K, Kulkarni AR: Plant system: nature's nanofactory. Colloids Surf. B Biointerfaces 2009, 73: 219–223. 10.1016/j.colsurfb.2009.05.018CrossRefGoogle Scholar
  54. 54.
    Gardea-Torresdey JL, Gomez E, Peralta-Videa JR, Parsons JG, Troiani H, Jose-Yacaman M: Alfalfa sprouts: a natural source for the synthesis of silver nanoparticles. Langmuir 2003, 19: 1357–1361. 10.1021/la020835iCrossRefGoogle Scholar
  55. 55.
    Shankar SS, Rai A, Ahmad A, Sastry M: Rapid synthesis of Au, Ag, and bimetallic Au core–Ag shell nanoparticles using Neem ( Azadirachta indica ) leaf broth. J. Colloid Interface Sci. 2004, 275: 496–502. 10.1016/j.jcis.2004.03.003CrossRefGoogle Scholar
  56. 56.
    Chandran SP, Chaudhary M, Pasricha R, Ahmad A, Sastry M: Synthesis of gold nanotriangles and silver nanoparticles using Aloe vera plant extract. Biotechnol. Prog. 2006, 22: 577–583. 10.1021/bp0501423CrossRefGoogle Scholar
  57. 57.
    Huang J, Li Q, Sun D, Lu Y, Su Y, Yang X, Wang H, Wang Y, Shao W, He N: Biosynthesis of silver and gold nanoparticles by novel sundried Cinnamomum camphora leaf. Nanotechnol. 2007, 18: 1–11.Google Scholar
  58. 58.
    Jain D, Kumar Daima H, Kachhwaha S, Kothari SL: Synthesis of plant-mediated silver nanoparticles using papaya fruit extract and evaluation of their anti microbial activities. Digest Journal of Nanomaterials and Biostructures 2009, 4: 557–563.Google Scholar
  59. 59.
    Sathishkumar M, Sneha K, Won SW, Cho C-W, Kim S, Yun Y-S: Cinnamon zeylanicum bark extract and powder mediated green synthesis of nano-crystalline silver particles and its bactericidal activity. Colloids Surf. B Biointerfaces 2009, 73: 332–338. 10.1016/j.colsurfb.2009.06.005CrossRefGoogle Scholar
  60. 60.
    Bar H, Bhui KD, Sahoo PG, Sarkar P, De PS, Misra A: Green synthesis of silver nanoparticles using latex of Jatropha curcas . Colloids Surf. A Physicochem. Eng. Asp. 2009, 339: 134–139. 10.1016/j.colsurfa.2009.02.008CrossRefGoogle Scholar
  61. 61.
    Ahmad N, Sharma S, Singh VN, Shamsi SF, Fatma A, Mehta BR: Biosynthesis of silver nanoparticles from Desmodium triflorum : a novel approach towards weed utilization. Biotechnology Research International 2011, 2011: 1–8. 10.4061/2011/454090CrossRefGoogle Scholar
  62. 62.
    Sathyavathi R, Krishna MB, Rao SV, Saritha R, Rao DN: Biosynthesis of silver nanoparticles using Coriandrum sativum leaf extract and their application in nonlinear optics. Adv. Sci. Lett. 2010, 3: 138–143. 10.1166/asl.2010.1099CrossRefGoogle Scholar
  63. 63.
    Mallikarjuna K, Dillip GR, Narasimha G, John Sushma N, Deva Prasad Raju B: Phytofabrication and characterization of silver nanoparticles from Piper betle broth. Res. J. Nanosci. Nanotechnol. 2012, 2: 17–23. 10.3923/rjnn.2012.17.23CrossRefGoogle Scholar
  64. 64.
    Kirsner R, Orsted H, Wright B: Matrix metalloproteinases in normal and impaired wound healing: a potential role of nanocrystalline silver. Wounds 2001, 13: 5–10.Google Scholar
  65. 65.
    Tian J, Wong KK, Ho CM, Lok CN, Yu WY, Che CM, Chiu JF, Tam PK: Tropical delivery of silver nanoparticles promotes wound healing. Chem. Med. Chem. 2007, 2: 129–136.CrossRefGoogle Scholar
  66. 66.
    Shin SH, Ye MK, Kim HS, Kang HS: The effects of nano-silver on the proliferation and cytokine expression by peripheral blood mononuclear cells. Int. Immunopharmacol. 2007, 7: 1813–1818. 10.1016/j.intimp.2007.08.025CrossRefGoogle Scholar
  67. 67.
    Burrell RE, McIntosh CL, Morris LR: Process of activating anti-microbial materials. Patent 1995, 5454886: 3.Google Scholar
  68. 68.
    Nano Bio Technology: Revolutionary medical bandage using nanotechnology to fight infection. (2010). Accessed 15 Sept 2012 http://nanobiotechnews.com/revolutionary-medical-bandage-using-nanotechnology-to-fight-infection.html (2010). Accessed 15 Sept 2012
  69. 69.
    Alt V, Bechert T, Steinrücke P, Wagener M, Seidel P, Dingeldein E, Scheddin D, Domann E, Schnettler R: Nanoparticulate silver. A new antimicrobial substance for bone cement. Orthopade 2004, 33: 885–892.CrossRefGoogle Scholar
  70. 70.
    Morley KS, Webb PB, Tokareva NV, Krasnov AP, Popov VK, Zhang J, Roberts CJ, Howdle SM: Synthesis and characterisation of advanced UHMWPE/silver nanocomposites for biomedical applications. Eur. Polym. J. 2007, 43: 307–314. 10.1016/j.eurpolymj.2006.10.011CrossRefGoogle Scholar
  71. 71.
    Cohen MS, Stern JM, Vanni AJ, Kelley RS, Baumgart E, Field D, Libertino JA, Summerhayes IC: In vitro analysis of a nanocrystalline silver-coated surgical mesh. Surg. Infect. 2007, 8: 397–403. 10.1089/sur.2006.032CrossRefGoogle Scholar
  72. 72.
    Brady MJ, Lissay CM, Yurkovetskiy AV, Sarwan SP: Persistent silver disinfectant for environmental control of pathogenic bacteria. Am. J. Infect. Control 2003, 31: 208–214. 10.1067/mic.2003.23CrossRefGoogle Scholar
  73. 73.
    Zhou W, Ma YY, Yang HA, Ding Y, Luo XG: A label-free biosensor based on silver nanoparticles array for clinical detection of serum p53 in head and neck squamous cell carcinoma. Int. J. Nanomed. 2011, 6: 381–386.CrossRefGoogle Scholar
  74. 74.
    Lee KJ, Nallathamby PD, Browning LM, Osgood CJ, Xu XHN: In vivo imaging of transport and biocompatibility of single silver nanoparticles in early development of zebra fish embryos. ACS Nano 2007, 1: 133–143. 10.1021/nn700048yCrossRefGoogle Scholar
  75. 75.
    Loo C, Lowery A, Halas N, West J, Drezek R: Immunotargeted nanoshells for integrated cancer imaging and therapy. Nano Lett. 2005, 5: 709–711. 10.1021/nl050127sCrossRefGoogle Scholar
  76. 76.
    Di Vincenzo GD, Giordano CJ, Schriever LS: Biologic monitoring of workers exposed to silver. Int. Arch. Occup. Environ. Health 1985, 56: 207–215. 10.1007/BF00396598CrossRefGoogle Scholar
  77. 77.
    Panyala NR, Pena-Mendez EM, Havel J: Silver or silver nanoparticles: a hazardous threat to the environment and human health? J. Appl. Biomed. 2008, 6: 117–129.Google Scholar
  78. 78.
    Allsopp M, Walters A, Santillo D: Nanotechnologies and Nanomaterials in Electrical and Electronic Goods: A Review of Uses and Health Concerns. Greenpeace Research Laboratories, London; 2007.Google Scholar
  79. 79.
    Hussain SM, Hess KL, Gearhart JM, Geiss KT, Schlager JJ: In vitro toxicity of nanoparticles in BRL 3A rat liver cells. Toxicol. In Vitro 2005, 19: 975–983. 10.1016/j.tiv.2005.06.034CrossRefGoogle Scholar
  80. 80.
    Soto KF, Murr LE, Garza KM: Cytotoxic responses and potential respiratory health effects of carbon and carbonaceous nanoparticulates in the Paso del Norte airshed environment. Int. J. Environ. Res. Public Health 2008, 5: 12–25. 10.3390/ijerph5010012CrossRefGoogle Scholar
  81. 81.
    Kone BC, Kaleta M, Gullans SR: Silver ion (Ag+)-induced increases in cell membrane K+ and Na+ permeability in the renal proximal tubule: reversal by thiol reagents. J. Membr. Biol. 1988, 102: 11–19. 10.1007/BF01875349CrossRefGoogle Scholar
  82. 82.
    McAuliffe ME, Perry MJ: Are nanoparticles potential male reproductive toxicants? A literature review. Nanotoxicol 2007, 1: 204–210. 10.1080/17435390701675914CrossRefGoogle Scholar
  83. 83.
    Burd A, Kwok CH, Hung SC, Chan HS, Gu H, Lam WK, Huang L: A comparative study of the cytotoxicity of silver-based dressings in monolayer cell, tissue explant, and animal models. Wound. Rep. Reg. 2007, 15: 94–104. 10.1111/j.1524-475X.2006.00190.xCrossRefGoogle Scholar
  84. 84.
    Kim YS, Song MY, Park JD, Song KS, Ryu HR, Chung YH, Chang HK, Lee JH, Oh KH, Kelman BJ, Hwang IK, Yu IJ: Subchronic oral toxicity of silver nanoparticles. Part. Fibre Toxicol. 2010, 7: 20. 10.1186/1743-8977-7-20CrossRefGoogle Scholar
  85. 85.
    Kittler S, Greulich C, Diendorf J, Köller M, Epple M: Toxicity of silver nanoparticles increases during storage because of slow dissolution under release of silver ions. Chem. Mater. 2010, 22: 4548–4554. 10.1021/cm100023pCrossRefGoogle Scholar
  86. 86.
    Senjen R: Nanosilver - a threat to soil, water and human health? Friends of the Earth Australia. (2007). Accessed 17 May 2012 http://nano.foe.org.au/sites/default/files/Nanosilver%20-%20a%20threat%20to%20soil,%20water%20and%20health%20March%202007.pdf (2007). Accessed 17 May 2012
  87. 87.
    Wood CM, Playle RC, Hogstrand C: Physiology and modeling of mechanisms of silver uptake and toxicity in fish. Environ. Toxicol. Chem. 1993, 18: 71–83.CrossRefGoogle Scholar
  88. 88.
    Asghari S, Johari SA, Lee JH, Kim YS, Jeon YB, Choi HJ, Moon MC, Yu IJ: Toxicity of various silver nanoparticles compared to silver ions in Daphnia magna . J. Nanobiotechnology 2012, 10: 14. 10.1186/1477-3155-10-14CrossRefGoogle Scholar

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© Prabhu and Poulose; licensee Springer. 2012

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Authors and Affiliations

  1. 1.Department of BiotechnologySri Venkateswara College of EngineeringSriperumbudurIndia

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