A novel jointly colorimetric and fluorescent sensor for Cu2+ recognition and its complex for sensing S2- by a Cu2+ displacement approach in aqueous media.

In this work, a simple and easily synthesized Schiff-based derivative colorimetric and fluorescent sensor (1), 4-dimethylamino-benzoic acid (2-imidazole formaldehyde)-hydrazide, was obtained for the detection of Cu2+ and S2-. The compound 1 exhibited dual spectral responses to Cu2+, that is, vivid color change and fluorescence enhancement in the presence of Cu2+. The detection limits were valued as 0.46 μM and 15 nM according to absorption and fluorescent response, respectively. Both of them are below the World Health Organization (WHO) guidelines for drinking water (31.5 μM). In addition, the ensemble (1-Cu2+) selectively and sensitively detected a low concentration of S2-. As the addition of S2- instantly removed Cu2+ from the ensemble (1-Cu2+) resulting in a color change from yellow to colorless and a "turn-off" fluorescent response. The detection limit for S2- was estimated as 0.12 μM (from fluorescent method) and 0.68 μM (from absorption method), respectively, each of which was also lower than the maximum allowable level of S2- (15 μM) in drinking water defined by the WHO. The binding process was confirmed via UV-vis absorption, fluorescence measurements, 1H NMR, mass spectroscopy and density functional theory calculation. What's more, successful practical application of test paper is used to inspect the S2- which means the convenient and rapid assay in real samples can be achieved.