Mechanisms of the pH dependent generation of hydroxyl radicals and oxygen induced by Ag nanoparticles

Many of the chemical and biological effects of silver nanoparticles (Ag NPs) are attributed to the generation of reactive oxygen species (ROS). ESR spectroscopy was used to provide direct evidence for generating ROS during decomposition of H2O2 assisted by Ag NPs. Hydroxyl radical formation was observed under acidic conditions and was accompanied by dissolution of Ag NPs. In contrast, evolution of O2 was observed in alkaline solutions containing H2O2 and Ag NPs; however, no net dissolution of Ag NPs was observed due to re-reduction of Ag+ as evidenced by a cyclic reaction. Since H2O2 is a biologically relevant product being continuously generated in cells, these results obtained under conditions mimicking different biological microenvironments may provide insights for finding new biomedical applications for Ag NPs and for risk assessment.