Bioreduction mechanism of silver nanoparticles.

The studies represent in-depth investigations of bacteria mediated reduction mechanism of silver nanoparticles (Ag NPs) not reported so far. Ag NPs were successfully synthesized by Bacillus subtilis spizizenni (NCIM 2063), and their bioreduction mechanism has been explored in detail. Optical absorption spectrum shows surface plasmon resonance peak in region 408-423 nm. FT-IR analysis of Ag NPs showed a peak at 3435 cm-1 which indicates the presence of N-H group (primary, secondary amines, and amides) on the surface of Ag NPs. XRD revealed the formation of a face-centered cubic crystal and hexagonal structure. TEM analysis indicates that bacterial, and media components affect size of nanoparticles. The detailed analysis of bioreduction mechanism was achieved using Sephadex G-25 column chromatography, HR-LCMS techniques, and nitrate reductase assay. The detection of capping agents was done by HR-MS. Result confirms the presence of nitrate reductase as well as other enzymes from bacterial supernatant and tripeptides from nutrient media involved in the reduction of silver. Furthermore, the confirmation of the origin of the tripeptides was investigated using BLAST technique. Three tripeptides (TYK, PFF, and YIF) from bacterial supernatant and one tripeptide (RWE) from nutrient media were detected on the surface of Ag NPs. Antibacterial efficiency of synthesized Ag NPs was evaluated against human pathogenic bacterial strains. Compared with other physical and chemical methods, the present method is cost-effective and environmentally benign using non-pathogenic bacteria.