Generation of reactive oxygen species induced by gold nanoparticles under x-ray and UV Irradiations

The radiosensitizing effect of 5--250 nm diameter Au nanoparticles (AuNPs) in water was investigated under irradiations of diagnostic x-ray and UV light. Enhanced generations of hydroxyl radical ( OH) and superoxide anion (O ₂ ^-) were confirmed from their dependencies on the absorbed energy, ethanol concentration and AuNPs' concentration. Two kinds of fluorescent probes revealed that the reactive oxygen species (ROS) generation rate under x-ray irradiation was enhanced by factors of 1.46 for OH and 7.68 for O ₂ ^-. Photo- and Auger electron charge transfer is possibly relevant to generation of O ₂ ^- near the particle surface, whereas fluorescent x-rays are involved in generation of OH in the secondary water radiolysis. Smaller diameter AuNPs with larger surface area showed a greater yield of ROS. An inverse proportion of ROS generation to the AuNPs' diameter suggests a catalytic function of AuNPs' surface for enhanced ROS generation. From the Clinical Editor: This paper investigates the effects of UV and X-ray irradiation on reactive oxygen species induction of gold nanoparticles, concluding that smaller diameter AuNPs with larger surface area lead to a greater yield of ROS probably due to catalytic effects. The paper may be important for the development of novel non-toxic radiation sensitizers.