Biosynthesis of Different Sizes of Silver Nanoparticles by Bacteria Screened from Cultivated Soil

Biosynthesis of metal nanoparticles (NPs) is an emerging area in the field of nano-biotechnology due to their unique properties and potential applications. Bacteria which produce extracellular stable metallic silver NPs were successfully enriched from cultivated soil, Kingdom of Bahrain, in the presence of AgNO3 (100 mM). The toxic Ag+ ion was reduced to non-toxic Ag0 NPs through bacterial nitrate reductase. When examined by UV-vis spectrophotometer, the silver NPs showed maximum peak at 421 nm which remained stable for several months. The presence of those highly stable silver NPs were confirmed by XRD analysis, optical microscope, SEM and EDS. The bacterial activity was followed for 25 days in the presence of different concentrations of silver nitrate (1-256 mM). Different sizes of silver NPs ranging between 5 to 30 nm were obtained. It was found that the size of the NPs can be controlled by changing the concentration of AgNO3.