An optical chemosensor for nano-level determination of Pb2+ and Cu2+ in aqueous media and its application in cell imaging

In this work, a colorimetric chemosensor containing thiazolidinedione as a biologically active molecule (NTCS) was successfully used for the highly selective and ultra-sensitive detection of Pb 2+ and Cu 2+ ions in different water samples as well as in a living cell both visually and optically. The characterization of the probe was confirmed by NMR, FT-IR spectroscopy, and UV–Visible absorption techniques prior to experiments. Probe NTCS exhibits an obvious color change because of a ligand to metal charge transfer (LMCT) complex that transforms it from colorless to yellow in the presence of Cu 2+ and from colorless to peach in complexation with Pb 2+ in aqueous methanol–water solutions that could make it a suitable ‘naked-eye’ indicator for Cu 2+ and Pb 2+ . Based on Job’s plot analysis, the interaction binding mode of probe NTCS with Cu 2+ (NTCS-Cu 2+ ) and Pb 2+ (NTCS-Ni 2+ ) was found to be 1:1 stoichiometry complex. The stability of probe-ligand in different pH ranges (9–11) was concerned with determination of the optimum pH for the detection of Cu 2+ , and Pb 2+ ions, which provides NTCS chemosensor suitable for quantitative analysis of the above-mentioned ions under physiological state. The results illustrated that the low detection limits (LOD) for Cu 2+ and Pb 2+ were calculated as 27.7 nM and 0.79 nM, respectively. In order to quick and convenient “naked-eye” detection of the Cu 2+ and Pb 2+ ions in pure aqueous media, low-cost NTCS-based test paper strips were successfully handed-down. MTT assay and bioimaging results indicated the probe has low toxicity, biocompatibility, and successful cellular absorption; hence, the probe can be used in Cu 2+ and Pb 2+ recognition in living cells with high selectivity and sensitivity compared to other chemosensors being researched in recent years. Graphical abstract