DOI 10.1515/ntrev-2014-0001 Nanotechnol Rev 2014; 3(3): 281–309 Review Mahendra Rai*, Sonal Birla, Avinash P. Ingle, Indarchand Gupta, Aniket Gade, Kamel Abd-Elsalam, Priscyla D. Marcato and Nelson Duran Nanosilver: an inorganic nanoparticle with myriad potential applications Abstract: Bionanotechnology is the field dealing with the Priscyla D. Marcato and Nelson Duran: Biological Chemistry synthesis and application of different nanomaterials. Nano­ Laboratory, Instituto de Química, Universidade Estadual de Campinas, CEP 13084862, Caixa Postal 6154, Campinas, S.P., Brazil particles usually form the core of nanobiomaterials. For the past decade, a variety of inorganic nanoparticles have been newly created to provide superior material properties. Nowadays, synthesis of nanoparticles is the area of interest 1 Introduction due to their physical, chemical, optical, electronic proper­ ties, and most importantly their larger surface area­to­vol­ ume ratio. Synthesis of inorganic nanoparticles is done by Nanotechnology is concerned with development and various physical and chemical processes, but biological utilization of structures and devices with organizational route of synthesis is gaining more importance due to their features at the intermediate scale between individual eco­friendly nature. Bioactivity of nanoparticles broadly molecules and about 100 nm where novel properties involves the wide range of nanoparticles and their biologi­ occur compared to bulk [1]. One nanometer (1 nm) is the cal application. They have been used as new tools not only one billionth part of a meter (10­9 m). To put that scale for investigation of biological processes but also for sensing in another context, the comparative size of a nanometer and treating diseases. In this respect, they are appearing to to a meter is same as that of the marble to the size of the be novel antimicrobial agents even against drug­resistant earth. Nanotechnology has capability to build up tailored microorganisms. On the other side at higher concentration, nanostructures and devices for given function by control they show toxicity to the humans and ecosystem. Therefore, at the atomic and molecular level. It is recognized as an in the present review, we have briefly described the synthe­ emerging and enabling technology of the 21st century, sis of different metal nanoparticles by different approaches in addition to the already established areas of informa­ mainly paying attention to their biosynthesis, antimicrobial tion technology and biotechnology. Nanotechnology is activity, and cytotoxicity. As silver nanoparticles are finding expected to open some new aspects to fight and prevent many applications among all of the inorganic nanoparti­ disease using atomic scale tailoring of materials [1]. cles, we paid special attention to them, too. Nanomaterials are at the top of the rapidly develop­ ing field of nanotechnology. The development of reliable Keywords: bioactivity; bionanotechnology; diversity; experimental protocols for the synthesis of nanomateri­ inorganic nanoparticles; toxicity. als over a range of chemical composition, size, and high monodispersity are the challenging issues in current nanotechnology [2]. There is an enormous interest in the *Corresponding author: Mahendra Rai, Department of synthesis of nanomaterials due to their unusual optical Biotechnology, Sant Gadge Baba Amravati University, Tapovan Road, Amravati – 444 602, Maharashtra, India, [3], chemical [4], photo­electrochemical [5], and electronic e-mail: [email protected] properties [6]. Different kinds of nanomaterials have been Sonal Birla, Avinash P. Ingle and Indarchand Gupta: Department developed as per the need for application purpose. Nano­ of Biotechnology, Sant Gadge Baba Amravati University, Tapovan particles exhibit a number of special properties relative Road, Amravati – 444 602, Maharashtra, India to bulk material and often have unique visible proper­ Aniket Gade: Department of Biology, Utah State University, Logan, UT 84322-5305, USA ties because they are small enough to confine their elec­ Kamel Abd-Elsalam: Unit of Excellence in Nano-Molecular Plant trons and produce quantum effects. The physicochemical, Pathology Research (ARC), Giza optical, and electronic properties of nanoparticle are the 282 M. Rai et al.: Nanosilver particles result of quantum confinement. Research on nanoparticles electrodes submerged in water [10]. The photolysis process is currently an area of intense scientific research. Various with nanosecond laser excitation in a silver colloidal solu­ strategies have employed to synthesize different inorganic tion has recently been used for synthesis of nanoparticles, nanoparticles. To develop pollution­free strategies for bio­ where as Courrol et al. [11] proposed the method for forma­ synthesis of nanoparticles, biotechnology plays an impor­ tion of silver nanoparticles using UV­LED, xenon lamp, and tant role and hence is called as “bionanotechnology.” sodium lamp excitation prior to nanosecond laser irradia­ This review is focused on the progress of bionano­ tion. Recently, Manikprabhu and Lingappa [12] reported the technology in terms of synthesis of nanoparticles and its microwave­assisted green synthesis of silver nanoparticles. bioactivities with special reference to antimicrobial activ­ ity. Here, we discuss the method of synthesis of nanopar­ ticles and possible mechanism of antimicrobial activity 2.2 Chemical synthesis against bacteria, fungi, and viruses. Moreover, we also explained the cytotoxicity of metallic nanoparticles. A wide range of techniques to fabricate nanoparticles have been developed rapidly over the past decade. There are diverse approaches for the preparation of the nanoscale materials that have been reported in the literature. Some 2 Different methods of synthesis of these methods include controlled chemical reduction of nanoparticles by ionic surfactant, electrochemical reduction, metal vaporization, sonochemical processing, solvent extrac­ Different methods like physical, chemical, and bio­ tion reduction, micro­emulsion technique, polyol pro­ logical have been employed for the synthesis of metal cesses, alcohol reduction, etc. nanoparticles. There are evidences which demonstrate that chemical methods are more effective as they provide better control over size, shape, and functionalization [13]. Reduction of 2.1 Physical synthesis metal salt in the presence of suitable capping agents such as polyvinyl pyrrolidone (PVP) is the common method Synthesis of metallic nanoparticles by the physical to generate metal nanocrystals. Solvothermal and other methods involve different approaches such as ball milling, reaction conditions were also employed for the synthe­ aerosol technology, lithography, arc discharge, laser abla­ sis, to exercise control over their size and shape of the tion, microwave irradiation by UV and IR radiations, etc. nanocrystals [14, 15]. Silver and gold nanoparticles were Typically, these techniques require the use of some sta­ prepared by a simple hand grinding method by using eth­ bilizer to protect nanoparticles against agglomeration. ylene glycol and poly vinyl alcohols as dispersion stabi­ Laser ablation known as liquid phase pulsed laser abla­ lizer [16]. Sun and Luo [17] and Amendola et al. [18] had tion (LP­PLA) technique is used to produce a wide range developed method for production of silver nanoparticles of novel materials, such as nano­diamond and related without using any reducing and stabilizing agent. nanocrystals, metallic nanocrystals, nanocrystal alloys, Icosahedral Au nanocrystals were obtained by the and metal oxides [7]. Silver and gold nanoparticles were reaction of HAuCl4 with PVP in aqueous media [19]. Right prepared by laser ablation of silicon (Si) target immersed bipyramidal nanocrystals (75–150 nm) of Ag have been pre­ in a water solution of respective metal salts (AgNO3 and pared by the addition of NaBr during the polyol reduction HAuCl4) [8]. Laser ablation in combination with the laser, of AgNO3 in the presence of PVP [20]. Cu nanoparticles of induces size control to nanoparticles, and provides versa­ pyramidal shape have been synthesized by electrochemical tile fully physical preparation method for gold nanoparti­ procedure [21]. Synthesis of FeNi3 nanoparticles by ambient cles with a broad size distribution of gold metal plate in chemical reduction were reported by Hongxia and group an aqueous solution of sodium dodecyl sulfate (SDS) [9]. [22]. Similarly, nanoparticles of Rh and Ir were successfully One of the most efficient physical methods for the prep­ prepared by the reduction of the appropriate compound in aration of nanoparticles was arc discharge. This method the ionic liquid, 1­n­butyl­3 methylimidazolium hexafluoro­ was found to be economical for the synthesis of metal phosphate, in the presence of hydrogen [23]. nanostructure in which there was no necessity of metal Metals like Au and Ag have almost identical lattice catalyst, explosive, corrosive gases, or vacuum equip­ constant, which was responsible for a strong tendency ment. Si nanowires and nanoparticles have been produced toward the alloy formation. The bimetallic particles will be by this method, using only arc discharge between two Si in core shell or alloy forms depending on the preparation M. Rai et al.: Nanosilver particles 283 conditions, miscibility, and kinetics of reduction of metal 2.3.1 Bacterial synthesis ions. Au­Ag was reported to form homogeneous alloy when reduced simultaneously. One step ahead,