The production of reactive oxygen species (ROS) by ultrasonic activation of nanomaterials has great potential in sonodynamic therapy and sonocatalysis. Herein, we first demonstrate that watersoluble Au 25 (Captril) 18 nanoclusters (NCs) can work as a sonosensitizer to produce singlet oxygen ( 1 O 2 ) under ultrasound irradiation. The ultrasonically mediated 1 O 2 production was also confirmed in other thiolated Au NCs, including those protected by glutathione or 6-aza-2thiothymine (ATT). There are two possible pathways to ultrasonically excite the thiolated Au NCs via microbubble cavitation: (i) sonoluminescence from water and (ii) ROS production (hydroxyl radical) by pyrolysis cleavage of water. We suggest that the sonoluminescence from water could excite the Au NCs to produce 1 O 2 under ultrasonication, when there is a spectral overlap between the sonoluminescence and the absorption of Au NCs to allow energy transfer. The ultrasonic excitation of ATT-Au NCs was confirmed by the observation of sonoluminescence. The Au(I)-SR shell of thiolated Au NCs is responsible for generating the triplet state of thiolated Au NCs to produce 1 O 2 under ultrasonication. As thiolated Au NCs also have photosensitizing capability, it would be used as ROS-based nanomedicine for a sonodynamic and/or photodynamic therapy.
The production of reactive oxygen species (ROS), such as hydroxyl radicals, by ultrasonic activation of semiconductor nanoparticles (NPs), including TiO2, has excellent potential for use in sonodynamic therapy and for the sonocatalytic degradation of pollutants. However, TiO2 NPs have limitations including low yields of generated ROS that result from fast electron–hole recombination. In this study, we first investigated the sonocatalytic activity of TiO2-supported Au nanoclusters (NCs) (Au NCs/TiO2) by monitoring the production of hydroxyl radicals (•OH) under ultrasonication conditions. The deposition of Au144 NCs on TiO2 NPs was found to enhance sonocatalytic activity for •OH production by approximately a factor of 2. Electron–hole recombination in ultrasonically excited TiO2 NPs is suppressed by Au144 NCs acting as an electron trap; this charge separation resulted in enhanced •OH production. In contrast, the deposition of Au25 NCs on TiO2 NPs resulted in lower sonocatalytic activity due to less charge separation, which highlights the effectiveness of combining Au144 NCs with TiO2 NPs for enhancing sonocatalytic activity. The sonocatalytic action that forms electron–hole pairs on the Au144/TiO2 catalyst is due to both heat and sonoluminescence from the implosive collapse of cavitation bubbles. Consequently, the ultrasonically excited Au144 (3 wt. %)/TiO2 catalyst exhibited higher catalytic activity for the production of •OH because of less light shadowing effect, in contrast to the lower catalytic activity when irradiated with only external light.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.