Extracellular biosynthesis of silver nanoparticles using cell filtrate of Streptomyces sp. ERI-3

In this study, we present a biological method for synthesis of silver nanoparticles (AgNPs) using Streptomyces sp. ERI-3 cell-filtrate. AgNO3 solution (1 mM) was added to the cell-free culture supernatant and the mixture was incubated at 28 °C for 48 h in the dark in an orbital shaker. The AgNPs were characterized using UV–visible spectroscopy, X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The nanoparticles exhibited maximum absorbance at 430 nm in UV–Vis spectroscopy. The XRD spectrum exhibited 2⊖2⊖ values corresponding to the silver nanocrystals. TEM and SEM micrographs revealed the extracellular formation of spherical nanoparticles in the size range of 10–100 nm. AgNPs formed flower-like self-assembled structures after three months incubating at room temperature in the dark. The study provides the evidence that the factors in the cell-free culture supernatant facilitate synthesis of AgNPs. This study is the first report on the biosynthesis of AgNPs using supernatant of Streptomyces sp. ERI-3 bacterium.