Sensing of zinc ions and sulfide using a highly practical and water-soluble fluorescent sensor: Applications in test kits and zebrafish

A novel practical fluorescent sensor AMPQ (2-((3-morpholinopropyl)amino)-N-((quinolin-8-yl)acetamide)) was designed and synthesized. In bis-tris buffer, AMPQ displayed highly practical and selective fluorescence recognition of Zn²⁺, clearly discriminating it from Cd²⁺ and other cations. Moreover, the AMPQ-Zn²⁺ complex exhibited a fluorescence "turn-off" response to S^2- with exceptional selectivity via a S^2--induced Zn²⁺ displacement approach. The detection limits (0.29 and 2.39 μM) of AMPQ for Zn²⁺ and S^2- were much lower than the WHO guidelines (76.0 and 14.7 μM), respectively. Importantly, sensor AMPQ could be applied in various practical applications such as in real water samples and test kits. In particular, AMPQ could monitor both Zn²⁺ and S^2- in live zebrafish, with a detection limit of 0.74 μM for Zn²⁺, which is the lowest among sensors previously reported for the relay detection of Zn²⁺ and S^2-. The sensing process of AMPQ toward Zn²⁺ and S^2- was evaluated by UV-vis and fluorescence spectroscopy, Job plots, ESI-MS, ¹H NMR titrations, and calculations.