Dark Reactive Oxygen Species Generation in ReVO₄:Eu³⁺ (Re = Gd, Y) Nanoparticles in Aqueous Solutions

Abstract

Nanomaterials, which promote the generation of reactive oxygen species (ROS) and precipitate the onset of oxidative stress responsible for the development of a variety of adverse conditions, have a great prospect for various nanomedicine applications. In this paper, for the first time, we report the pro-oxidant activity of GdYVO4:Eu3+ and GdVO4:Eu3+ nanoparticles (NPs) in water solutions without any external stimuli (in the darkness). This dark pro-oxidant activity is shown to be associated with superoxide (O2•–) and hydroxyl radical (•OH) generation and is dependent on the size of NPs and, consequently, the concentration of surface defects, such as oxygen vacancies VO. For small 2 nm GdYVO4:Eu3+ NPs, strong O2•– and •OH radical production has been revealed, whereas for larger GdVO4:Eu3+ NPs, low level of O2•– and negligible level of •OH radical production have been detected during the sample storage in the darkness. The possible mechanisms of the dark ROS generation in ReVO4:Eu3+ NPs are considered.