EPR study of visible light-induced ros generation by nanoparticles of ZnO

Nanoparticles of ZnO have been shown to have marked antibacterial and anticancerous activities. The toxic effect of ZnO has been found to exist due to a reaction of the ZnO surface with water. In the present work electron-spin resonance measurements revealed that aqueous suspensions of small nanoparticles of ZnO produce increased levels of reactive oxygen species, namely hydroxyl radicals and singlet oxygen. Interestingly, a remarkable enhancement of the oxy radicals, was detected when the ZnO water suspension had been irradiated with blue (400-500 nm) light. The characterization of the mechanism of light-induced oxy radicals formation by ZnO nanoparticles would contribute to its use as a sterilization agent.