Bacterial indoleacetic acid-induced synthesis of colloidal Ag 2 O nanocrystals and their biological activities.

The biosynthesis and biological activity of colloidal Ag2 O nanocrystals have not been well studied, although they have potential applications in many fields. For the first time, we developed a reducing agent free, cost-effective technique for Ag2 O biosynthesis using Xanthomonas sp. P5. The optimal conditions for Ag2 O synthesis were 50 °C, pH 8, and 2.5 mM AgNO3 . Using these conditions the yield of Ag2 O obtained at 10 h was about five times higher than that obtained at 12 h under unoptimized conditions. Ag2 O was characterized by FESEM-EDS, TEM, dynamic light scattering, XRD, and UV-Visible spectroscopy. Indoleacetic acid produced by the strain P2 was involved in the synthesis of Ag2 O. Ag2 O exhibited a broad antimicrobial spectrum against several human pathogens. Furthermore, Ag2 O exhibited 1,1-diphenyl-2-picrylhydrazyl (IC50  = 25.1 µg/ml) and 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonate (IC50  = 16.8 µg/ml) radical scavenging activities, and inhibited collagenase (IC50  = 27.9 mg/ml). Cytotoxicity of Ag2 O was tested in fibroblast cells and found to be non-toxic, demonstrating biocompatibility.