Mechanism of Microbial Synthesis of Nanoparticles

Nanotechnology is a field of research dealing with synthesis, strategy and manipulation of structures from approximately 1 to 100 nm in size. Metal nanoparticles (NPs), especially silver nanoparticles, have received attention for their extensive applications in the biomedical and physicochemical fields (Singh et al. 2016). Metal nanoparticles are synthesized by physical, chemical and biological methods (Zhang et al. 2016). In physical methods, nanoparticles are prepared by evaporation-condensation using a tube furnace at atmospheric pressure, while in reduction and other types of chemical synthesis, three main components such as metal precursors, reducing agents and stabilizing/capping agents are used. Moreover, the reduction of silver ions includes nucleation and subsequent growth (Deepak et al. 2011). Both physical and chemical techniques involve the use of a high amount of energy or hazardous reagents, which are disadvantages of these approaches (Ahmed et al. 2016). Green synthesis explores the biological pathway and resources such as plant extracts, algae, yeasts, fungi and bacteria for bioproduction of nanoparticles. Thus, biogenic synthesis of nanoparticles offers an interesting alternative to chemical synthesis as it is regarded as safe, cost-effective, sustainable and environment-friendly (Chokriwal et al. 2014, Singh et al. 2016). The biological agents secrete a huge number of enzymes, which are able to hydrolyze metals and thus bring about enzymatic reduction of metals ions (Chokriwal et al. 2014, Gahlawat and Choudhury 2019). Researchers suggest that nanoparticles are synthesized when the microorganisms grab target ions from their environment and turn the metal ions into the element metal through enzymes (Li et al. 2011). Nanoparticles synthesized by biological approach are coated and stabilized by natural molecules such as amino acids, proteins or secondary metabolites, which are released from cells of organisms performing this process (Narasimha et al. 2013, Gurunathan 101et al. 2014, Gahlawat and Choudhury 2019). Capping proteins attach to the surface of nanoparticles through free amino groups or cysteine residues, which consequently prevents the aggregation of nanoparticles and preserves their properties (Sanjenbam et al. 2014).