pH-dependent preparation of glutathione-protected gold nanoclusters with different fluorescent emission and their application on Hg2+ detection

Gold nanoclusters (AuNCs) have attracted significant interest due to their unique fluorescence properties in the environmental monitoring field. In this work, we report the first pH-dependent preparation of glutathione-protected AuNCs (Glu-AuNCs) with different fluorescent emission. The Glu-AuNCs shows the intense yellow emission from samples pH 1.0–5.5, and red emission from samples pH 11.0 to 12.5, respectively. The size of AuNCs depends on the pH of the reaction solution. The characterizations of UV–vis and photoluminescent (PL) spectra show the size of AuNCs increases with increasing samples pH value. The strongly red-emitting Glu-AuNCs were applied to detect Hg 2+ ions by fluorescence quenching. Owing to the specific Hg 2+ -Glu interactions, the fluorescent AuNCs protected by the interference biothiol, Glu, showed superior selective detection of Hg 2+ . The red-emitting Glu-AuNCs provided high sensitivity for Hg 2+ detection with widely linear range of 0–20 μM and a detection limit of 1.6 nM (0.32 ppb), which is compared with the reported data in literature. To show a potentially practical application, the developed assay method was applied to detect Hg 2+ in real samples and a certified reference material. The developed simple method for Hg 2+ detection with high selectivity and sensitivity opens a new idea for other sensor development.