**Abstract**

Nanotechnology is an expanding area of research where we use to deal with the materials in Nano-dimension. The conventional procedures for synthesizing metal nanoparticles need to sophisticated and costly instruments or high-priced chemicals. Moreover, the techniques may not be environmentally safe. Therefore "green" technologies for synthesis of nanoparticles are always preferred which is simple, convenient, eco-friendly and cost effective. Green synthesis of nanoparticle is a novel way to synthesis nanoparticles by using biological sources. It is gaining attention due to its cost effective, ecofriendly and large scale production possibilities. Silver nanoparticles (AgNPs) are one of the most vital and fascinating nanomaterials among several metallic nanoparticles that are involved in biomedical applications. It has vital importance in nanoscience and naomedicines to treat and prevent vital disease in human beings especially in cancer treatment. In current work we discussed different methods for synthesis of AgNPs like biological, chemical and physical along with its characterization. We have also discussed vital importance of AgNPs to cure life threatnign diseases like cancer along with antidiabetic, antifungal, antiviral and antimicrobial alog with its molecular mode of action etc. Finally we conclude by discussing future prospects and possible applications of silver nano particles.

**Keywords:** green synthesis, silver nanoparticles, nonmaterials, anticancer and antidiabetic

#### **1. Introduction**

Currently, improving and protecting our environment using green chemistry have become important issues in many fields of research. The most promising approach for generating new fields in biomedical sciences is the pharmaceutical application of nanoparticles (NPs) [1]. Due to ascension of industrial era and explosion of world population large amount of hazardous chemicals and gases released in environment in which adversely affecting our nature. Due avoid this and to protect our nature currently we world is focusing on development of natural products nanoparaticles. Biomolecules are highly compatible with nanotechnology which makes unique assembly for development of metal nanoparticles of biological molecules which are

authentic and coast effective [2]. From the ancient era noval medicinal potential of silver has been known and proven for its antimicrobial potential [3]. Silver nano particles (AgNPs) and its related products were tremendously venomous and showed broad spectrum antibacterial potential against sixteen bacterial species [4, 5]. Nanotechnology is future era in material science which develops and upgrades qulaites of particles such as size, and morphology which provide entry of nonmaterial in future quality material building in almost every field [6]. Nanotechnologies have been used to develop nanoparticles-based targeted drug carriers [7]. Metal nanoparticles have a high specific surface area and a high fraction of surface atoms because of the unique physicochemical characteristics of nanoparticles [8, 9]. In that they include catalytic activity, optical properties and electronic properties, antibacterial properties, and magnetic properties [10, 11]. The nanoscale materials have emerged as novel "antimicrobial agents" due to their high surface area to volume ratio and their unique chemical and physical properties [12, 13]. In recent years development of metallic nanoparicles is an emerging field of research in material science. Crystalline nanosilver gained prime importance and has superior applicability in detection of biomolecules, antibacterial, electronics, diagnostic applications in health care system etc. Apart from novel applicability of AgNPs researchers still in search of advance methods to synthesize eco-friendly and coast effective tools to develop AgNPs [14, 15]. As silver posse's broad spectrum potential against bacterial and microbial species which specially utilized in industries it has key role in healthcare systems [16]. Nitrate group of silver potentially responsible for its broad spectrum antibacterial potential and as it convert in to AgNPs surface area is drastically increased which improve microbial exposure time and area [17–19]. Different techniques are available to synthesize AgNPs such as physical, chemical and biological. Though chemical method is rapid it utilizes capping agents for synthesis which is costly and produces adverse and toxic effects. This demands development of safe, ecofriendly, coast effective tool for synthesis of AgNPs and focused on biological methods such as green synthesis which is non toxic and developed using plant origin materials and overcomes disadvantages of earlier approaches. Moreover, use of plant extracts also reduces the cost of microorganism's isolation and culture media enhancing the cost competitive feasibility over nanoparticles synthesis by microorganisms [20]. Applicability of AgNPs is primly due to its nanoscale size and shape as compared to bulk. Due to these unique properties researchers are hunting of novel methods to synthesize AgNPs with prissily controllable size and shape [21–24]. Apart from excellent inhibitory potential of AgNPs in recent years most of the pathogenic bacteria developed resistant against it which is major concern of health care system. Chemical and physical approaches consumes ample of time, energy, money and generate toxic side effects. Nowadays green synthesis utilize microbes, fungi and medicinal plants which are easily available, convenient to handle and wide source of metabolites to synthesize AgNPs gained prime importance due to its nontoxic and ecofriendly properties [25]. Currently AgNPs are synthesized from natural herbs having medicinal potential such as synthesis of various metal nanoparticles using fungi like *Aspergillus terreus*, *Paecilomyces lilacinus* and *Fusarium* [26]. *Penicillium* sp. [27] *Fusarium oxysporum* [28] and *Euphorbia hirata*, green tea, neem, starch aloevera, lemon etc. [29–32]. AgNPs mainly binds to cell wall and penetrate deep inside the cell wall which produces cellular damage by interacting with DNA, proteins inside the cell which leads to cell death [33–37].

#### **2. Need for green synthesis and silver nanoparticles**

Silver is a basic element which is non-toxic belonging thermal and electrical potential [38]. Silver demand will likely to rise as silver find new uses, particularly

**63**

*Silver Nanoparticles: Properties, Synthesis, Characterization, Applications and Future Trends*

in textiles, plastics and medical industries, surgical, dental resigns, coated water filters, sanitizers, detergents, soap and wound dressings. Applicability in healthcare for treatment of mental illness, convulsions, de addiction of narcotic products along with sexually transmitted diseases like syphilis and gonorrhea leads to changing the pattern of silver emission as these technologies and products diffuse through the global economy [39–41]. Green synthesis is an emerging approach which overcomes demerits of physiochemical approaches by utilization of natural herbs which are nontoxic [42, 43]. Green synthesized nanosilver offer many advantages like utilization of phytochemicals, antioxidants acts as naturally occurring reducing agents, coast efficient, large scale manufacturing highly beneficial and usage of toxic chemicals, high pressure, energy are avoided. Nanosilver can be engineered by different techniques such as irradiation, reduction, electrochemical and chryochemical synthesis. Nanosilver can be molded in to desired shapes and bear unique properties like permeability by pH and dissolved ions as compare to routine metals [44, 45]. As AgNPs generate larger surface area per unit mass which improves contact time nanosilver customer market an demand drastically raised in wide verity of indus-

tries along with healthcare, food packing, textiles, cosmetics etc. [46].

**4. Methods for synthesis of silver nanoparticle**

Generally AgNPs are nanoparticles of silver having size range between 1 and 100 nm in size having unique properties such as electrical, optical and magnetic having wide range of applicability [47]. Green chemistry is and encouraging approach mainly utilize nanosilver along with natural biomolecules such as

polysaccharides, tollens which overcomes drawbacks of conventional methods and produce AgNPs which are ecofriedly, nontoxic and coast effective [48, 49]. Metallic silver ions are inactive but once it come contact with reducing agent ionization occurs and it get converted in its active form. Ionic silver is active form of silver which binds to cell wall of bacteria leading to major structural changes in cell morphology. AgNPs causes de-naturation of RNA and DNA replication which further leads to cell death [50]. Silver is also called as oligodynamic due to its bactericidal potential at minimum concentration. That's why it has been largely used in medical

In physical approach of synthesis of AgNPs evaporation and condensation has major importance. Temperature gradient play important role in cooling of vapors at desired rate. A chance of contamination by solvent has been removed by physical approach as no solvent has been used in physical method and uniform distribution of particle size precisely obtained [53, 54]. Minimum inhibitory concentration in toxicity studies can be easily achieved by production of nano scale nanoparticles in high concentration [55]. AgNPs also synthesized by laser ablation of metallic particles [56]. One important advantage of laser ablation technique compared to other methods for production of metal colloids is the absence of chemical reagents in solutions. Therefore, pure and uncontaminated metal colloids for further applications can be prepared by this technique [57]. Wide range of material can be synthesized in nanoparticels by physical method such as Au, Au and PbS etc. Synthesis of AgNPs by tube furnace has ample of disadvantages such as require larger space,

*DOI: http://dx.doi.org/10.5772/intechopen.99173*

**3. Silver nano particles**

products [51, 52].

**4.1 Physical approaches**

*Silver Nanoparticles: Properties, Synthesis, Characterization, Applications and Future Trends DOI: http://dx.doi.org/10.5772/intechopen.99173*

in textiles, plastics and medical industries, surgical, dental resigns, coated water filters, sanitizers, detergents, soap and wound dressings. Applicability in healthcare for treatment of mental illness, convulsions, de addiction of narcotic products along with sexually transmitted diseases like syphilis and gonorrhea leads to changing the pattern of silver emission as these technologies and products diffuse through the global economy [39–41]. Green synthesis is an emerging approach which overcomes demerits of physiochemical approaches by utilization of natural herbs which are nontoxic [42, 43]. Green synthesized nanosilver offer many advantages like utilization of phytochemicals, antioxidants acts as naturally occurring reducing agents, coast efficient, large scale manufacturing highly beneficial and usage of toxic chemicals, high pressure, energy are avoided. Nanosilver can be engineered by different techniques such as irradiation, reduction, electrochemical and chryochemical synthesis. Nanosilver can be molded in to desired shapes and bear unique properties like permeability by pH and dissolved ions as compare to routine metals [44, 45]. As AgNPs generate larger surface area per unit mass which improves contact time nanosilver customer market an demand drastically raised in wide verity of industries along with healthcare, food packing, textiles, cosmetics etc. [46].

#### **3. Silver nano particles**

*Silver Micro-Nanoparticles - Properties, Synthesis, Characterization, and Applications*

with DNA, proteins inside the cell which leads to cell death [33–37].

Silver is a basic element which is non-toxic belonging thermal and electrical potential [38]. Silver demand will likely to rise as silver find new uses, particularly

**2. Need for green synthesis and silver nanoparticles**

authentic and coast effective [2]. From the ancient era noval medicinal potential of silver has been known and proven for its antimicrobial potential [3]. Silver nano particles (AgNPs) and its related products were tremendously venomous and showed broad spectrum antibacterial potential against sixteen bacterial species [4, 5]. Nanotechnology is future era in material science which develops and upgrades qulaites of particles such as size, and morphology which provide entry of nonmaterial in future quality material building in almost every field [6]. Nanotechnologies have been used to develop nanoparticles-based targeted drug carriers [7]. Metal nanoparticles have a high specific surface area and a high fraction of surface atoms because of the unique physicochemical characteristics of nanoparticles [8, 9]. In that they include catalytic activity, optical properties and electronic properties, antibacterial properties, and magnetic properties [10, 11]. The nanoscale materials have emerged as novel "antimicrobial agents" due to their high surface area to volume ratio and their unique chemical and physical properties [12, 13]. In recent years development of metallic nanoparicles is an emerging field of research in material science. Crystalline nanosilver gained prime importance and has superior applicability in detection of biomolecules, antibacterial, electronics, diagnostic applications in health care system etc. Apart from novel applicability of AgNPs researchers still in search of advance methods to synthesize eco-friendly and coast effective tools to develop AgNPs [14, 15]. As silver posse's broad spectrum potential against bacterial and microbial species which specially utilized in industries it has key role in healthcare systems [16]. Nitrate group of silver potentially responsible for its broad spectrum antibacterial potential and as it convert in to AgNPs surface area is drastically increased which improve microbial exposure time and area [17–19]. Different techniques are available to synthesize AgNPs such as physical, chemical and biological. Though chemical method is rapid it utilizes capping agents for synthesis which is costly and produces adverse and toxic effects. This demands development of safe, ecofriendly, coast effective tool for synthesis of AgNPs and focused on biological methods such as green synthesis which is non toxic and developed using plant origin materials and overcomes disadvantages of earlier approaches. Moreover, use of plant extracts also reduces the cost of microorganism's isolation and culture media enhancing the cost competitive feasibility over nanoparticles synthesis by microorganisms [20]. Applicability of AgNPs is primly due to its nanoscale size and shape as compared to bulk. Due to these unique properties researchers are hunting of novel methods to synthesize AgNPs with prissily controllable size and shape [21–24]. Apart from excellent inhibitory potential of AgNPs in recent years most of the pathogenic bacteria developed resistant against it which is major concern of health care system. Chemical and physical approaches consumes ample of time, energy, money and generate toxic side effects. Nowadays green synthesis utilize microbes, fungi and medicinal plants which are easily available, convenient to handle and wide source of metabolites to synthesize AgNPs gained prime importance due to its nontoxic and ecofriendly properties [25]. Currently AgNPs are synthesized from natural herbs having medicinal potential such as synthesis of various metal nanoparticles using fungi like *Aspergillus terreus*, *Paecilomyces lilacinus* and *Fusarium* [26]. *Penicillium* sp. [27] *Fusarium oxysporum* [28] and *Euphorbia hirata*, green tea, neem, starch aloevera, lemon etc. [29–32]. AgNPs mainly binds to cell wall and penetrate deep inside the cell wall which produces cellular damage by interacting

**62**

Generally AgNPs are nanoparticles of silver having size range between 1 and 100 nm in size having unique properties such as electrical, optical and magnetic having wide range of applicability [47]. Green chemistry is and encouraging approach mainly utilize nanosilver along with natural biomolecules such as polysaccharides, tollens which overcomes drawbacks of conventional methods and produce AgNPs which are ecofriedly, nontoxic and coast effective [48, 49]. Metallic silver ions are inactive but once it come contact with reducing agent ionization occurs and it get converted in its active form. Ionic silver is active form of silver which binds to cell wall of bacteria leading to major structural changes in cell morphology. AgNPs causes de-naturation of RNA and DNA replication which further leads to cell death [50]. Silver is also called as oligodynamic due to its bactericidal potential at minimum concentration. That's why it has been largely used in medical products [51, 52].

#### **4. Methods for synthesis of silver nanoparticle**

#### **4.1 Physical approaches**

In physical approach of synthesis of AgNPs evaporation and condensation has major importance. Temperature gradient play important role in cooling of vapors at desired rate. A chance of contamination by solvent has been removed by physical approach as no solvent has been used in physical method and uniform distribution of particle size precisely obtained [53, 54]. Minimum inhibitory concentration in toxicity studies can be easily achieved by production of nano scale nanoparticles in high concentration [55]. AgNPs also synthesized by laser ablation of metallic particles [56]. One important advantage of laser ablation technique compared to other methods for production of metal colloids is the absence of chemical reagents in solutions. Therefore, pure and uncontaminated metal colloids for further applications can be prepared by this technique [57]. Wide range of material can be synthesized in nanoparticels by physical method such as Au, Au and PbS etc. Synthesis of AgNPs by tube furnace has ample of disadvantages such as require larger space,

high power, rapid rise of environmental temperature etc. AgNPs synthesized by laser ablation strongly depend on laser wavelength, time of laser pulse, laser fluence, the ablation time duration and the effective liquid medium. Ejection of AgNPs synthesized by laser ablation requires little power and particle size is precisely depends on laser fluence. However morphology, size and shape of AgNPs mainly depend on contact of laser light passing. Also, the formation of nanoparticles by laser ablation is terminated by the surfactant coating. The nanoparticles formed in a solution of high surfactant concentration are smaller than those formed in a solution of low surfactant concentration. One advantage of laser ablation compared to other conventional method for preparing metal colloids is the absence of chemical reagents in solutions. Therefore, pure colloids, which will be useful for further applications, can be produced by this method [58, 59].

### **4.2 Chemical approaches**

Chemical reduction is the most frequently applied method for the preparation of AgNPs as stable, colloidal dispersions in water or organic solvents. Most commonly used reductant is citrate. In aqueous solution reduction of silver occurs and nanosize colloidal silver ions are generated. Stability of any colloidal dispersion has prime importance and which could be achieved by stabilizing agent (dodecanethiol) which adsorbed on surface and produce protective sheath. It can avoid agglomeration and crystal growth of the system. During the synthesis of AgNPs minute changes in parameters (Polymers) makes drastic changes in size, shape, morphology, polydispersibility index, self assembling and zeta potential (Stability). Frequently used ingredients in synthesis of AgNPs and AuNPs are glycol derivatives Polyvinyl pyrrolidone (PVP) and Polyethylene glycol (PEG). Polyacrylamide play dual function such as reducing and stabilizing agent in synthesis of AuNPs [59, 60]. Surfactants containing functional groups such as amines, thoils and acids play important role in stability of colloidal dispersion which protects the system from crystal growth, coaleseces and agglomeration. Currently AuNPs developed by modified tollens method utilize saccharides and silver hydrosols and reducing agent which yield AgNPs in the range of 50–200 nm and 20–50 nm respectively [61].

#### **4.3 Biological approaches**

Biotechnology is an emerging tool to develop biological synthesis of AgNPs. Besides this magnetic nanoparticles has great antibacterial potential due to improved surface area to treat raised microbial resistant against many antibiotics and medicines [62]. Currently green chemistry is rapidly growing technique utilized for synthesis of AgNPs with naturally occurring stabilizing, reducing and capping agents to synthesize AgNPs without toxic adverse effects [63]. Reduction of metal ions by combined efforts of herbs and certain enzymes, proteins, microorganisms, bacteria and fungi etc. in biological synthesis has been successfully reported [64].

#### **4.4 Synthesis of silver nanoparticles by fungi**

High production yield AgNPs synthesized by fungi obtained when compared to bacteria due to fungi secret higher amount of proteins that directly responsible for increased production [65]. Higher production rate is mainly due to silver ions entered in to fungal cell wall which leads to reduction of silver ions by fungal

**65**

**Figure 1.**

*Biological methods of silver nanoparticles.*

*Silver Nanoparticles: Properties, Synthesis, Characterization, Applications and Future Trends*

enzymes such as naphthoquinones and anthraquinones [66]. Slower rate and process is only disadvantage associated with fungal synthesis of AgNPs hence green

*Pseudomonas stutzeri* which is the first strain of bacteria form which AgNPs were synthesized and isolated form Ag amine [68]. Many of the bacterial strains and microorganism developing resistance to metal at lower concentration. Resistance mainly produced due to efflux, change in solubility, toxicity via oxidation/reduction and precipitation of metals [69]. There are evidences that at lower conc. Microorganisms are alive but once exposed to high conc. Metal ions leads to microbial death. In biosynthesis of silver enzyme nitrate reductase convert nitrate

Green synthesis is an excellent tool that can be utilized for synthesis of AgNPs

as it uses natural origin medicinal herbs and its extracts which contain wide range of metabolites specifically water soluble flavones, quiones causes rapid rapid and quick reduction of silver when compared to fungi and microbes. Green chemistry approach is safe, cosat efficient, easily scalable to mass productions, easily availability of raw materials at cheaper coast. Phytochemicals directly take part in reduction process of the silver ions a during synthesis of AgNPs

synthesis approach is more preferred over the other techniques [67].

*DOI: http://dx.doi.org/10.5772/intechopen.99173*

to nitrite [70].

(**Figure 1**) [71].

**4.5 Synthesis of silver nanoparticles by bacteria**

**4.6 Synthesis of silver nanoparticles by plants**

*Silver Nanoparticles: Properties, Synthesis, Characterization, Applications and Future Trends DOI: http://dx.doi.org/10.5772/intechopen.99173*

enzymes such as naphthoquinones and anthraquinones [66]. Slower rate and process is only disadvantage associated with fungal synthesis of AgNPs hence green synthesis approach is more preferred over the other techniques [67].

### **4.5 Synthesis of silver nanoparticles by bacteria**

*Silver Micro-Nanoparticles - Properties, Synthesis, Characterization, and Applications*

applications, can be produced by this method [58, 59].

**4.2 Chemical approaches**

and 20–50 nm respectively [61].

**4.4 Synthesis of silver nanoparticles by fungi**

**4.3 Biological approaches**

reported [64].

high power, rapid rise of environmental temperature etc. AgNPs synthesized by laser ablation strongly depend on laser wavelength, time of laser pulse, laser fluence, the ablation time duration and the effective liquid medium. Ejection of AgNPs synthesized by laser ablation requires little power and particle size is precisely depends on laser fluence. However morphology, size and shape of AgNPs mainly depend on contact of laser light passing. Also, the formation of nanoparticles by laser ablation is terminated by the surfactant coating. The nanoparticles formed in a solution of high surfactant concentration are smaller than those formed in a solution of low surfactant concentration. One advantage of laser ablation compared to other conventional method for preparing metal colloids is the absence of chemical reagents in solutions. Therefore, pure colloids, which will be useful for further

Chemical reduction is the most frequently applied method for the preparation of AgNPs as stable, colloidal dispersions in water or organic solvents. Most commonly used reductant is citrate. In aqueous solution reduction of silver occurs and nanosize colloidal silver ions are generated. Stability of any colloidal dispersion has prime importance and which could be achieved by stabilizing agent (dodecanethiol) which adsorbed on surface and produce protective sheath. It can avoid agglomeration and crystal growth of the system. During the synthesis of AgNPs minute changes in parameters (Polymers) makes drastic changes in size, shape, morphology, polydispersibility index, self assembling and zeta potential (Stability). Frequently used ingredients in synthesis of AgNPs and AuNPs are glycol derivatives Polyvinyl pyrrolidone (PVP) and Polyethylene glycol (PEG). Polyacrylamide play dual function such as reducing and stabilizing agent in synthesis of AuNPs [59, 60]. Surfactants containing functional groups such as amines, thoils and acids play important role in stability of colloidal dispersion which protects the system from crystal growth, coaleseces and agglomeration. Currently AuNPs developed by modified tollens method utilize saccharides and silver hydrosols and reducing agent which yield AgNPs in the range of 50–200 nm

Biotechnology is an emerging tool to develop biological synthesis of AgNPs.

High production yield AgNPs synthesized by fungi obtained when compared to bacteria due to fungi secret higher amount of proteins that directly responsible for increased production [65]. Higher production rate is mainly due to silver ions entered in to fungal cell wall which leads to reduction of silver ions by fungal

Besides this magnetic nanoparticles has great antibacterial potential due to improved surface area to treat raised microbial resistant against many antibiotics and medicines [62]. Currently green chemistry is rapidly growing technique utilized for synthesis of AgNPs with naturally occurring stabilizing, reducing and capping agents to synthesize AgNPs without toxic adverse effects [63]. Reduction of metal ions by combined efforts of herbs and certain enzymes, proteins, microorganisms, bacteria and fungi etc. in biological synthesis has been successfully

**64**

*Pseudomonas stutzeri* which is the first strain of bacteria form which AgNPs were synthesized and isolated form Ag amine [68]. Many of the bacterial strains and microorganism developing resistance to metal at lower concentration. Resistance mainly produced due to efflux, change in solubility, toxicity via oxidation/reduction and precipitation of metals [69]. There are evidences that at lower conc. Microorganisms are alive but once exposed to high conc. Metal ions leads to microbial death. In biosynthesis of silver enzyme nitrate reductase convert nitrate to nitrite [70].

#### **4.6 Synthesis of silver nanoparticles by plants**

Green synthesis is an excellent tool that can be utilized for synthesis of AgNPs as it uses natural origin medicinal herbs and its extracts which contain wide range of metabolites specifically water soluble flavones, quiones causes rapid rapid and quick reduction of silver when compared to fungi and microbes. Green chemistry approach is safe, cosat efficient, easily scalable to mass productions, easily availability of raw materials at cheaper coast. Phytochemicals directly take part in reduction process of the silver ions a during synthesis of AgNPs (**Figure 1**) [71].

**Figure 1.** *Biological methods of silver nanoparticles.*
