BSA-capped gold nanoclusters as potential theragnostic for skin diseases: Photoactivation, skin penetration, in vitro, and in vivo toxicity

BSA-capped gold nanoclusters are promising theragnostic systems that can be excited to render both fluorescence emission and reactive oxygen species. Although their synthesis and photoluminescence properties are already well described, more accurate information about their use as photosensitizers is required in order to advance towards health applications. In this work, we have obtained BSA-capped gold nanoclusters and characterized their photophysics by different techniques. Singlet oxygen production was detected upon irradiation, which was enough to produce toxicity on two cell lines. Remarkably, an internal energy transfer, probably due to the presence of smaller nanoclusters and the contribution of oxidized residues of BSA in the system, caused fluorescence emission near 640 nm after excitation in the UV range. Additionally, the system was capable of penetrating human skin beyond the stratum corneum, which enhances the potential of these nanoclusters as bifunctional photodynamic therapy effectors and biomarkers with application in a diversity of skin diseases. In the absence of radiation, BSA-capped gold nanoclusters did not cause toxicity in vitro, while their toxic effect on an in vivo model as zebrafish was determined.