Intramolecular Charge Transfer of Gold Nanoclusters for pH Indicating

The investigation of the intramolecular charge transfer (ICT) process of gold nanoclusters (AuNCs) is critical to understand the unique features of the nanomaterials, which also benefits their further applications. Herein, 6-methyl-2-thiouracil (CH3-2-TU) and polyvinylpyrrolidone (PVP)-stabilized AuNCs are prepared, and the ICT behaviors are carefully studied. Protonation or deprotonation of the ligands around AuNCs could be used to regulate the ICT state, influencing the electron distribution and band gap. Shifted fluorescence emission phenomena are thus observed, which respond to external pH stimuli. In addition, the AuNCs are developed as color-switchable indicators for the highly sensitive detection of biogenic amines. As a proof of concept, the performance of this strategy in the evaluation of food spoilage by probing pH conditions is validated with satisfactory results. The discoveries in this work offer a convenient route to regulate the optical properties of AuNCs and the design of pH-based sensing applications.