Facile One-Pot Synthesis of Au/Ag Bimetallic Nanoclusters as a Fluorescent Probe for the Detection of Hg2+ and Cu2+

Fluorescent metal nanoclusters show great promise in heavy metal ion sensing. Herein, a bimetallic nanocluster (GSH-Au/Ag NCs) with orange fluorescence was synthesized through a facile one-pot method. The synthesized GSH-Au/Ag NCs displayed optimal excitation and emission peaks at 275 and 610 nm, respectively. The incorporation of silver can enhance the fluorescence of metal nanoclusters. The fluorescence of as-synthesized GSH-Au/Ag NCs can be significantly quenched by Hg2+ and Cu2+, and a “on–off” fluorescent probe was designed. The detection conditions, including pH and the concentration of the probe, were optimized. The respective detection limits for Hg2+ and Cu2+ ions under optimal detection conditions are estimated to be 40 nM and 33 nM, over the linear range of 100–1200 nM. Furthermore, a ratiometric fluorescent probe was prepared by mixing quinine sulfate and as-synthesized GSH-Au/Ag NCs. Hg2+ and Cu2+ can effectively quench the red fluorescence of GSH-Au/Ag NCs, whereas the blue fluorescence of quinine sulfate remains invariant. This leads to measurable changes in the RGB values of the resulting fluorescence images. The ratio (R/B) exhibits a linear relationship with the concentration of Hg2+ and Cu2+, enabling the determination of its concentration by analyzing RGB values in fluorescence images. This visual detection method significantly reduces both assay time and cost, making it suitable for on-site detection of heavy metal ions in water samples.