The importance of biological agents has been recognized as a promising tool for green synthesis of silver nanoparticles over conventional physiochemical methods that are laden with various type of drawbacks. The biomediated nanoparticles synthesis chiefly employing microorganisms and plants as nanofactories is gaining worldwide popularity over past few decades. Biosynthesized silver nanoparticles have demonstrated desirable physical and chemical and antimicrobial properties among other metallic nanoparticles. This article represents a comprehensive review of biosynthesis route for silver nanoparticles formation including the mechanism, extra- and intra-cellular types and remarkable outcomes of previously conducted research works on biosynthesis. Broad antimicrobial spectra including antibacterial, antifungal, antiviral, sporicidal of biosynthesized silver nanoparticles with major emphasis on their potential applications in biocatalysis, biosensing, food packaging and preservation, pest killing and plant growth promotion, biomedicine and diagnostics etc. have been discussed. Moreover, this article also encompasses meticulous description on challenges and future prospects of biosynthesis of nanoparticles.

Biosynthesis of silver nanoparticles (AgNPs) using plant extracts has become a promising alternative to the conventional chemical synthesis approach. In this study, cost-effective synthesis of AgNPs was attempted using leaves extract of Litchi chinensis. Bio-reduction reaction for the synthesis of NPs was checked by confirming the presence of AgNPs in solution by UV-vis spectrophotometry and with further characterization by fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Surface plasmon resonance (SPR) band showed absorption peak at 422 nm indicating the formation of AgNPs, and FTIR spectra confirmed the presence of biological molecules involved in AgNPs synthesis. TEM analysis revealed the spherical shape of AgNPs with particle size distribution in a range of 5–15 nm. Further, the biosynthesized AgNPs showed significant bactericidal and sporicidal activity against model spore former Bacillus subtilis. AgNPs at concentrations ranging from 25 to 100 µg/mL showed bactericidal activity with inhibition zone ranging from 4–19 mm and sporicidal activity at 100–200 µg/mL in a range of 4.46–61.6% with an exposure time of 2–8 h. These findings exhibit distinctive potential of biogenic AgNPs for their efficient use in developing novel bactericidal and sporicidal agent against spore forming bacilli.