Abstract

Two novel fluorescent probes for Cu²⁺ detection have been developed based on thiazoline-quinoline conjugates bearing a 4-ethynyl-N,N-dimethylaniline unit (QT1 and QT2). QT2 exhibits instantaneous fluorescence quenching of Cu²⁺ with an emissive change from bright orange to arctic blue under UV light irradiation (365 nm). The plots of I<inf>0</inf>/I against Cu²⁺ concentrations show a good linear relationship that ranges from 0 to 50 µM with a coefficient of determination (R²) = 0.9906 and a limit of detection (LOD) of 76 nM, which is considered low (4.84 ppb). A 1:1 complexation between QT2 and Cu²⁺ was confirmed by UV–Vis titration, ESI-MS, and SC-XRD. The QT2·Cu²⁺ complex was dissociated by the addition of EDTA. The fluorescence quenching mechanism involves the ligand-to-metal charge transfer (LMCT) of a paramagnetic Cu²⁺ complex. The QT2 probe on a paper-based strip was used to determine the amount of Cu²⁺ in water and food samples (shiitake mushrooms and oysters).