A general strategy for specific sensing of Sn²⁺ in environmental water samples and in cells

Sn²⁺ pollution poses significant risks to ecosystems and human health, necessitating the development of simple detection methods for accurate monitoring of Sn²⁺ dynamics. Here, we developed a conceptually distinct strategy that exploits the Sn²⁺-mediated reduction of organic azides rather than conventional chelation mechanism, and constructed a series of azide-based fluorescent probes (A-G) operating via turn-on, ratiometric, or fluorescence resonance energy transfer modality with emissions spanning blue to near-infrared for specific sensing of Sn²⁺. These probes exhibit exceptional selectivity for Sn²⁺ over Sn⁴⁺ and other biologically relevant species, sub-micromolar detection limits (as low as 13.7 nM), fast response kinetics (t_1/2 < 1 min), and full aqueous compatibility. The reduction mechanism was confirmed through radical trapping and product isolation. Probe B enabled direct quantify Sn²⁺ in real water samples with good recovery (93.5-103.3 %). All designed probes facilitated high-contrast in-situ imaging of Sn²⁺ in living cells. This work provides a robust platform for deciphering the environmental fate and biological roles of Sn²⁺.