A quinoline-based fluorescent chemosensor for distinguishing cadmium from zinc ions using cysteine as an auxiliary reagent

A quinoline-based fluorescent chemosensor was reported for the simultaneous detection of Zn²⁺ and Cd²⁺ in aqueous solution. In HEPES buffer, among various metal ions, only Zn²⁺ and Cd²⁺ exhibited fluorescence enhancement at 497 nm accompanied by the red-shift emission wavelength. The mechanism was proposed that internal charge transfer effect induced by binding with Zn²⁺ or Cd²⁺ produced the fluorescence changes. With the addition of cysteine, the fluorescent solution containing sensor and Cd²⁺ show the decreased fluorescence at 497 nm and the increased fluorescence at 420 nm, which was attributed to the dissociation of the complex formed by sensor and Cd²⁺. In contrast, the fluorescence of solution containing sensor and Zn²⁺ is unchanged with the addition of Cys. Furthermore, the confocal microscopy experiments indicated that this sensor can provide real-time detection for intracellular Zn²⁺ and Cd²⁺.