A simple quinoline-derived fluorescent sensor for the selective and sequential detection of copper(ii) and sulfide ions and its application in living-cell imaging

Abstract

A simple amide compound (QLBA), prepared from quinoline-2-carboxylic acid and 2-(1H-benzo[d]imidazol-2-yl)aniline, was synthesized and evaluated as an efficient fluorescence chemosensor for the selective recognition of copper ions (Cu2+). This sensor could detect Cu2+ in CH3OH/HEPPES buffer in a wide pH range (4.0–10.0), with obvious fluorescence quenching. The obtained QLBA–Cu2+ complex could be used as a new cascade sensor for detecting sulfide anions (S2−). The corresponding detection limits were found to be 2.2 × 10−7 M for Cu2+ and 4.6 × 10−7 M for S2−. The sensing mechanisms of QLBA toward Cu2+ were systematically investigated in detail by NMR, HR-MS analysis, and density functional theory (DFT) calculations. In addition, this sensor was verified to be of low cytotoxicity and to have good imaging characteristics for the detection of Cu2+ and further for the recognition of S2− in living cells, suggesting that QLBA was a useful tool for tracking Cu2+ and S2− ions in vivo.