Highly selective and sensitive ratiometric near-infrared fluorescent probe for real-time detection of Hg2+ and its bioapplications in live cells

A ratiometric near-infrared (NIR) fluorescent probe L based on chromenylium-cyanine fluorophore with chelate unit NS2O2 for the detection of Hg2+ ions in aqueous media has been prepared. The probe L shows high selectivity for Hg2+ ions with immediately fluorescence intensity increasing at 663 nm and decreasing at 728 nm synchronously via a Hg2+-induced intramolecular charge transfer (ICT) mechanism, leading to both naked-eye and ratiometric detection of Hg2+ ions in real time. At the same time, the probe exhibits a high sensitivity to Hg2+ in a concentration of ppb range with detection limit of 9.59 nM. Moreover, the probe is cell permeable and low toxic, and can be used in living cells for ratiometric visual monitoring of Hg2+ ions by confocal laser scanning fluorescence microscopy.