Probing hydroxyl radical generation from H2O2 upon plasmon excitation of gold nanorods using electron spin resonance: Molecular oxygen-mediated activation

Gold nanostructures are among the noble metal nanomaterials being intensely studied due to their good biocompatibility, tunable localized surface plasmon resonance (SPR), and ease of modification. These properties give gold nanostructures many potential chemical and biomedical applications. Herein, we demonstrate the critical role of oxygen activation during the decomposition of hydrogen peroxide (H2O2) in the presence of photoexcited gold nanorods (AuNRs) by using electron spin resonance (ESR) techniques. Upon SPR excitation, O-2 is activated first, and the resulting reactive intermediates further activate H2O2 to produce aEuro cent OH. The reactive intermediates exhibit singlet oxygen-like (O-1(2)-like) reactivity, indicated by O-1(2)-specific oxidation reaction, quenching behaviors, and the lack of the typical O-1(2) ESR signal. In addition, by using the antioxidant sodium ascorbate (NaA) as an example, we show that hydroxyl radicals from H2O2 activation can induce much stronger NaA oxidation than that in the absence of H2O2. These results may have significant biomedical implications. For example, as oxidative stress levels are known to influence tumorigenesis and cancer progression, the ability to control redox status inside tumor microenvironments using noble metal nanostructures may provide new strategies for regulating the metabolism of reactive oxygen species and new approaches for cancer treatment.