Generation of hydroxyl radicals from photothermal decomposition of H₂O₂ initiated by gold nanorods and its applications for cellular oxidative damage

The features of localized surface plasmon resonance (LSPR) excited by plasmonic nanoparticles have been actively explored in the fields of energy, environment, and nanomedicine. One unique effect of LSPR excitation is to convert absorbed light into local heat via a photothermal effect. Herein, we demonstrate that the local photothermal effect of gold nanorods (AuNRs) can decompose hydrogen peroxide (H₂O₂) to generate hydroxyl radicals (·OH). Two methods based on the electron spin resonance (ESR) technique were developed to characterize the average local temperature (T_local) around the excited gold nanorods: (1) temperature-dependent ·OH generation from thermal decomposition of H₂O₂, and (2) 4-oxo-2,2,6,6-tetramethylpiperidine-d16-1-15N-oxyl (¹⁵N-PDT) linewidth change from collisions with paramagnetic molecular O₂. The T_local obtained was 20–30 °C higher than the global temperature (T_global) of the irradiated suspension measured using a thermocouple. The generation of ·OH could be modulated by pH, H₂O₂ concentration, AuNR concentration, and laser power. Finally, as a proof-of-concept, we produced cellular oxidative damage using ·OH obtained from the photothermal decomposition of H₂O₂ by resonant excited AuNRs. Considering its unique spatiotemporal controllability, the local photothermal effect of plasmonic nanostructures has great potential for precision medicine.