Applications of Glutathione-Capped Gold Nanoclusters in Heterogeneous Catalytic Reduction of 4-Nitrophenol and Fluorescent Sensing of Mercury Ions

Three glutathione-capped gold nanoclusters (GSH-AuNCs) with orange-red luminescence and an average size of approximately 2 nm were synthesized by modulating reaction temperature and time. Under 416 nm excitation, all three clusters exhibited strong, single broad-spectrum emission. Owing to their small size and high surface area, the GSH‑AuNCs displayed high catalytic activity for the reduction of 4‑nitrophenol (4‑NP). A combined experimental and density functional theory (DFT) study revealed that the size‑dependent activity originates from differences in the adsorption energy of the reaction product, providing a mechanistic structure‑activity relationship. Furthermore, based on the specific Hg–Au metallophilic interaction, the GSH‑AuNCs served as a sensitive fluorescent sensor for selective mercury ion (Hg2+) detection. By comparing the fluorescence quenching responses of clusters synthesized under different conditions, the optimal preparation parameters for gold nanoclusters with efficient Hg2+fluorescence sensing were identified. This work not only offers a strategy for tailoring AuNC properties through synthesis control but also demonstrates their dual functionality in catalysis and environmental sensing.