A novel fluorescent “OFF-ON” sensing strategy for Hg (II) in water based on functionalized gold nanoparticles

Mercury ion (Hg 2+ ) is a heavy metal pollutant that can affect the safety of water environment and endanger human health. A novel detection strategy (GNPs- L -Cys-Rh6G2) for Hg 2+ based on a fluorescence “OFF-ON” was proposed. Gold nanoparticles (GNPs) were assembled with l -cysteine ( L -Cys), which was used as a “bridge” to link with rhodamine 6G derivatives (Rh6G2). The fluorescence state transition of GNPs- L -Cys-Rh6G2 switching from “OFF”-“ON” was observed because Hg 2+ opened the spirolactam ring through a catalytic hydrolysis mechanism. The fluorescence signal of the GNPs- L -Cys-Rh6G2 system mixed with Hg 2+ in the concentration range of 10–100 μM was analyzed and determined with a limit of detection (LOD) of 2 μM ( S/N  = 3). Moreover, the spiked Hg 2+ concentration in real water samples were successfully quantified by GNPs- L -Cys-Rh6G2, which was in line with the ideal average recovery rate and relative standard deviation. The proposed strategy exhibited high specificity, sensitivity and stability, providing a novel sensing platform for heavy metal ions detection in water environment.