Controlled redox-activity of small orthovanadate nanocrystals

Nanocrystals, which promote generation of reactive oxygen species (ROS) and stimulate the onset of oxidative stress responsible for the development of a variety of adverse conditions, are of great prospect for various nanomedicine applications. ROS generation in semiconducting nanocrystals is a complex process, the efficiency of which is governed by both nanocrystals characteristics (size, morphology, etc.) and external conditions, such as type of irradiation. On the other hand, in nanocrystals characterized by high amount of structural defects, for instance, oxygen vacancies (VO) in oxide nanocrystals, such defects could serve as traps for charge carriers and are responsible for ROS production in nanocrystals even without UV irradiation (in the dark). In our previous works, we have shown that GdYVO₄:Eu³⁺ nanocrystals exhibit photo-catalytic activity (ROS production) at both UV-light irradiation [1, 2] and in the dark condition [3]. In this work, we report controlled redox-activity of small (d=2nm) GdYVO₄:Eu³⁺ nanocrystals in aqueous solutions and biological environment. It has been revealed that depending on pre-treatment conditions (exposure to UV light or storage in the darkness), the same nanocrystals exhibit pro- or antioxidant properties. Pro-/antioxidant activity in aqueous solutions was evaluated by UV-vis spectroscopy by the ascorbic acid (AA) oxidation test, and hydroxyl radical (•OH) generation analysis. Lipid oxidation under the effect of nanocrystals have been also analyzed. Multi-functional GdYVO₄:Eu³⁺ nanocrystals with controlled redox-activity are assumed to be a new theranostic agent in radiotherapy. (author)