Ultrasensitive Hg ²⁺ Detection Using High Quantum Yield DNA‐Templated Silver Nanoclusters for Environmental Monitoring

Mercury ions (Hg 2+ ) pose severe environmental and health risks due to their persistence, bioaccumulation, and neurotoxicity. Here, we report a fluorescent probe for ultrasensitive Hg 2+ detection, constructed from cytosine‐rich hairpin DNA‐templated silver nanoclusters (hpDNA/Ag NCs). Through multiparameter optimization (DNA/Ag + stoichiometry, reduction kinetics, surface passivation, and the DNA template design), the hpDNA/Ag NCs achieve a high quantum yield of 72.55% and exceptional stability, retaining fluorescence even after 3 months. The probe exhibits a linear response to Hg 2+ (0.1–50 nM) with a 0.03 nM detection limit, which is enabled by selective fluorescence quenching via thymine–Hg 2+ –thymine coordination and Ag/Hg amalgam formation. Rigorous interference tests confirm specificity against 15 competing ions, including Ag + and Pb 2+ . Successful application in spiked environmental water samples demonstrates recovery rates of 96%–106%, validating its practicality for real‐world monitoring. This work establishes a cost‐effective, sensitive, and field‐deployable platform for Hg 2+ detection, addressing critical gaps in environmental pollution control.