We first demonstrated that, contrary to common belief, the presence of gold nanoparticles (AuNPs) in solution does not increase the quantity of radicals produced under irradiation for a given dose [Shcherbakov2020]. Furthermore, experiments show that these raw, unfunctionalized nanoparticles are not chemically neutral and actually prove to be excellent catalysts that can modify the usual reaction pathways. For example, in the case of the hydroxylation reaction of acetanilide in the presence of O2, the addition of AuNPs causes a 40-fold decrease in the formation of the reaction product. This is an unexpected observation because, in the absence of AuNPs, O2 is known to promote hydroxylation reactions (Figure). However, the oxidation of vitamin C, which is an electron donor, is accelerated more than 1000 times in the presence of AuNPs [Shcherbakov2023]. Our observations show that AuNPs in the presence of O2 promote the oxidation of electron-donating species such as radicals or certain molecules present in the biological environment. Therefore, it can be expected that AuNPs may also alter cellular metabolism by oxidizing organic radicals naturally produced in the cell or by oxidizing electron-donating molecules present in its environment. This catalytic activity at room temperature, which has so far been overlooked when introducing AuNPs into biological environments, must now be considered to understand the reaction mechanisms involved during radiosensitization by these nanoparticles and, potentially, to clarify many experimental results that have remained unexplained until now [Shcherbakov2021a, Shcherbakov2021b].