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.