Biosynthesis of Silver Nanoparticles by Streptomyces griseorubens isolated from Soil and Their Antioxidant Activity.

Microbial mediated biological synthesis of metallic nanoparticles was carried out ecofriendly in the present study. Silver nanoparticles (AgNPs) were extracellularly biosynthesised from Streptomyces griseorubens AU2 and extensively characterised by ultraviolet-visible (UV-vis) and Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy and X-ray diffraction analysis. Elemental analysis of nanoparticles was also carried out using energy dispersive X-ray spectroscopy. The biosynthesised AgNPs showed the characteristic absorption spectra in UV-vis at 422 nm which confirmed the presence of metallic AgNPs. According to the further characterisation analysis, the biosynthesised AgNPs were found to be spherical and crystalline particles with 5-20 nm average size. Antioxidant properties of the biosynthesised AgNPs were determined by 2,2-diphenyl-1-picrylhydrazyl free radical scavenging assay and was found to increase in a dose-dependent matter. The identification of the strain was determined by molecular characterisation method using 16s rDNA sequencing. The present study is the first report on the microbial biosynthesis of AgNPs using S. griseorubens isolated from soil and provides that the active biological components found in the cell-free culture supernatant of S. griseorubens AU2 enable the synthesis of AgNPs.