X-ray Induced Hydroxyl Radical Generation by GdYVO₄:Eu³⁺ Nanoparticles in Aqueous Solution: Main Mechanisms

• Main Authors: Pavel O. Maksimchuk, Svetlana L. Yefimova, Valeriia V. Omielaieva, Kateryna O. Hubenko, Vladimir K. Klochkov, Oleksandr D. Opolonin, Yuri V. Malyukin
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: Crystals
• Subjects: nanocrystals; X-ray irradiation; hydroxyl radical generation; radioprotective effect
• Online Access: https://www.mdpi.com/2073-4352/10/5/370
• ISSN: 2073-4352

We report on strong X-ray-induced hydroxyl radical (^.<inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">O</mi> <mi mathvariant="normal">H</mi> </mrow> </semantics> </math> </inline-formula>) generation in an aqueous solution containing UV light pre-treated GdYVO₄:Eu³⁺ nanoparticles (L-GdYVO). The methods of optical spectroscopy were used to detect ^.<inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">O</mi> <mi mathvariant="normal">H</mi> </mrow> </semantics> </math> </inline-formula> in the solutions. The complex nature of the mechanism of ^.<inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">O</mi> <mi mathvariant="normal">H</mi> </mrow> </semantics> </math> </inline-formula> generation has been revealed and discussed. The experimental data obtained indicate that the mechanism of ^.<inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">O</mi> <mi mathvariant="normal">H</mi> </mrow> </semantics> </math> </inline-formula> generation is associated with two main processes: (i) direct ^.<inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">O</mi> <mi mathvariant="normal">H</mi> </mrow> </semantics> </math> </inline-formula> generation with the participation of thermalized h⁺ formed at X-ray irradiation, and (ii) X-ray-facilitated jumps of h⁺ formed in the nanoparticles’ (NPs’) valence band at UV light pre-treatment and trapped in local levels formed by random scattering potential. At the same time, for GdYVO₄:Eu³⁺ nanoparticles, which were not exposed to UV light before the X-ray irradiation (D-GdYVO), a strong radioprotective effect ascribed to the electron-donation properties of V⁴⁺ ions was observed. Thus, depending on the pre-treatment condition, we can change the redox properties of GdYVO₄:Eu³⁺ NPs in an opposite direction, which makes this nanomaterial a unique theranostic agent for radiation therapy (RT) enhancement, allowing the problem of radiation therapy (RT)-resistant hypoxic tumours to be overcome.