Green synthesis and characterization of monodispersed silver nanoparticles obtained using oak fruit bark extract and their antibacterial activity

Green synthesis of silver nanoparticles (Ag NPs) has been achieved using oak fruit bark extract as a reducing, capping and stabilizing agent. The biosynthesized Ag NPs were characterized using various techniques. UV-visible spectrum of prepared silver colloidal solution showed absorption maximum at 433 nm. X-ray diffraction and transmission electron microscopy analysis revealed that Ag NPs have a face-centred cubic structure being spherical in shape with an average particle size of 20-25 nm. The toxicity of the Ag NPs was tested on bacterial species such as Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli by comparison based on diameter of inhibition zone in disc diffusion tests and minimum inhibitory concentration and minimum bactericidal concentration of NPs dispersed in liquid cultures. The antimicrobial activity of Ag NPs was greater towards Gram-positive bacteria (S. aureus and B. subtilis) compared to Gram-negative bacteria as determined using standard Kirby-Bauer disc diffusion assay and serial dilution. Copyright (C) 2016 John Wiley & Sons, Ltd.