Gold nanoclusters with enhanced near-infrared emission and its application as sensors for biological molecules.

Ultrasmall gold nanoclusters (NCs) have been engineered as a new kind of functional material due to their excellent photoluminescence properties. However, the synthesis of highly luminescent water-soluble nanoclusters with near-infrared (NIR) emission remains limited. Herein, we developed a pH-regulated strategy to facilitate the construction of self-assemblies with enhanced luminescence based on aggregation-induced emission (AIE) strategy. Using 2-mercaptobenzoic acid (MBA) as reductant and stabilizer, the original weakly luminescent AuNCs exhibited intense emission by adjusting pH controllably. The formation of compact organized nanostructures could effectively restrict the rotation and vibration of capping ligands by non-covalent interactions, which reduced the nonradiative relaxation from excited states and finally improved the emission properties of AuNCs. Moreover, the assemblies possess many intriguing features including bright NIR luminescence and excellent biocompatibility, which could be used as luminous probes in biological molecules sensing (tyrosinase (TYR) and dopamine (DA)) and promising candidates for cell imaging. This study provides a simple and feasible strategy for developing metal NCs-based smart optical materials in the field of bioscience.