Real-time probing of mercury using an efficient "turn-on" strategy with potential as in-field mapping kit and in live cell imaging

Based on a rhodamine scaffold as a fluorophore and 2-aminothiazole as a receptor, we present a highly selective and sensitive sensor (TS). An enhanced photophysical response (fluorescence as well as absorption) accompanied by high sensitivity and selectivity was observed upon interaction of TS with Hg²⁺ among various competitive cations (Ag⁺, Al³⁺, Ba²⁺, Ca²⁺, Co³⁺, Co²⁺, Cd²⁺, Fe³⁺, Fe²⁺, K⁺, Li⁺, Mg²⁺, Mn²⁺, Cu²⁺, Pb²⁺, Ni²⁺, Na⁺ and Zn²⁺) in CH₃CN : H₂O (7 : 3 v/v, HEPES buffer 10 mM pH 7.0). The synthesized sensor can detect Hg²⁺ as low as 0.326 μM with a complexation constant of 2.37 × 10⁶ M^-1. This complexation between TS and Hg²⁺ is reversible in the presence of ethylenediaminetetraacetate (EDTA). Furthermore, single crystal X-ray diffraction (XRD) and Job's plot results show a 1 : 1 binding stoichiometry. The most interesting feature of the sensor is the real-time determination of Hg²⁺ in real contaminated water. Furthermore, the fabricated sensor can be employed as an intracellular monitoring agent for live cell imaging of the HeLa cell line.