Gold nanomaterials exhibiting size-dependent optical and catalytic properties are extensively used in sensors, catalysts, and photodevices. Yet, the size effect of gold nanoclusters (AuNCs) on 1O2 production has rarely been explored. This study demonstrates that lysozyme (LYZ)-stabilized Au8 clusters could serve as a photosensitizer for the efficient production of 1O2 under the irradiation of green light-emitting diode relative to the LYZ-stabilized Au25 clusters and gold nanoparticles (AuNPs; approximately 3.2 nm). The same stabilizing macromolecule, LYZ, was used as a template for preparing AuNCs, enabling the comparison of their 1O2 production efficiency resulting from ligand effects without complications. 9,10-Anthracenediyl-bis(methylene)dimalonic acid was used to detect 1O2 by monitoring its absorption peak intensity with time. The QYs for 1O2 generation were determined to be 16.2%, 3.0%, and 8 clusters, Au25 clusters, and AuNPs, respectively, using Rose Bengal (RB) as a reference. Electron spin resonance spectroscopy confirmed that the photoexcitation of Au8 clusters afforded 1O2 rather than other reactive oxygen species, and their 1O2 production efficiency increased with decreasing excitation wavelength. The mechanism behind these observations indicated that the positive surface charge of the LYZ-stabilized Au8 clusters at pH 5.0 promoted the approach of O2 molecules to the cluster surface and thus facilitated efficient 1O2 generation. Additionally, the relatively large surface-to-volume ratio of the LYZ-stabilized Au8 clusters, compared to that of the LYZ-stabilized Au25 clusters, could be a contributing factor for enhanced 1O2 generation.
Santhoshkumar et al. (Thu,) studied this question.