Highly red-emitting gold nanoclusters rapidly synthesized in aqueous phase: Effects of precursor quality and detection of Hg2+

Metal nanoclusters have attracted considerable interest due to their unique fluorescence properties in the fields of environmental monitoring, chemical detection and biosensing. In this study, we developed a rapid synthesis method for highly red-emitting gold nanoclusters (AuNCs) via direct reduction of precursor HAuCl₄ by sodium borohydride in presence of glutathione (GSH) at 0 °C. Our results demonstrated that the precursor quality had an important effect on the luminescence properties of the AuNCs, only the samples derived from high-purity precursors (99.9 % and 99.99 %) emitted strong red fluorescence. The obtained AuNCs can be excited in a broad range of 250–600 nm and can emit fluorescence of 560–730 nm. The maximum fluorescence quantum yield of the AuNCs derived from 99.99 % precursor achieved a high value of 9.98 %. Additionally, these fluorescent nanoclusters exhibited high selectivity toward Hg²⁺ by quenching. A linear calibration range of 10–100 μM Hg²⁺ was demonstrated with a limit of detection (LOD) of 1.45 μM using the as-obtained AuNCs as fluorescence probes, and in a narrowed range of 1–25 μM Hg²⁺, a LOD of 0.13 μM was determined using the diluted nanoclusters as probes. These results offer a significant reference for the synthesis and application of the AuNCs as fluorescence nanoprobes.