Track analysis of a synchrotron X‐ray photoelectric nanoradiator by in situ fluorescence imaging of reactive oxygen species: comparative study of gold and iron oxide nanoparticles

The emission of fluorescent X‐rays and low‐energy electrons by mid‐/high‐ Z nanoparticles upon irradiation with either X‐ray photons or high‐energy ion beams is referred to as the nanoradiator effect (NRE). A track analysis of NRE was performed using reactive oxygen species (ROS) gels, to which macrophages containing gold nanoparticles (AuNPs) were attached, together with single‐cell irradiation of the intracellular nanoparticles from a microbeam of synchrotron X‐rays, and the range and distribution of OH and O 2 produced were compared with those of the Fe‐nanoradiator by magnetite nanoparticles (FeONP, Fe 3 O 4 ). The Au‐nanoradiator generated ROS fluorescence to a greater depth and wider angle with respect to the incident X‐rays than that of the Fe‐nanoradiator. The ROS‐oxidant fluorescence intensity ratios of OH to O 2 were different for the AuNPs and FeONPs, reflecting different relative yields of electrons and fluorescent X‐rays from NRE. In the region immediately (<100 µm) below the irradiated cell, OH‐radicals were distributed mainly along two or three tracks in the depth direction in the FeONP‐ or AuNP‐ROS gel. In contrast, O 2 was scattered more abundantly in random directions in the AuNP‐ROS gel than in the FeONP‐ROS gel. Track analysis of X‐ray photoelectric nanoradiator radiation showed a different range of dose distribution and relative emission compositions between Au‐ and Fe‐nanoradiators, suggesting more extensive damage beyond a single cell containing AuNPs than one containing FeONPs.