Aggregation/Self-Assembly-Induced Approach for Efficient AuAg Bimetallic Nanocluster-Based Photosensitizers

Great efforts have been devoted to the exploration of potential diagnostic and therapeutic applications of thiolate-protected gold nanoclusters (Au NCs). One of the therapeutic applications is the photosensitized generation of highly reactive singlet oxygen (O-1(2)) using Au NCs for photodynamic therapy. However, there is scope for improving the O-1(2)-generation efficiency of Au NC photosensitizers. In this study, we exploit three strategies to improve the O-1(2)-generation efficiency of glutathione-protected Au NCs: (i) doping with silver (i.e., using bimetallic AuAg NCs, (ii) achieving aggregation-induced emission (AIE) using a Au(I)-thiolate complex, and (iii) achieving self-assembly-induced emission (SALE) using a polymer nanogel. The combination of these three effects dramatically increased the O-1(2)-generation efficiency and enhanced the luminescence of the glutathione-protected Au NCs, owing to the inhibition of the nonradiative decay pathways. Finally, the photosensitizers based on AuAg NC@nanogel composites were successfully used for antimicrobial photodynamic therapy (a-PDT) against oral bacteria. This study provides general insights into the molecular design of water-soluble Au NC photosensitizers for therapeutic applications.