A Retrievable and Highly Selective Fluorescent Probe for Monitoring Sulfide and Imaging in Living Cells

A novel selective fluorescent chemosensor based on an 8-hydroxyquinoline-appended fluorescein derivative (L1) was synthesized and characterized. Once combined with Cu2+, it displayed high specificity for sulfide anion. Among the various anions, only sulfide anion induced the revival of fluoresecence of L1, which was quenched by Cu2+, resulting in "off-on"-type sensing of sulfide anion. What's more, the sensor was retrievable to indicate sulfide anions with Cu2+, and S2-, in turn, increased. With the addition of Cu2+, compound L1 could give rise to a visible pink-to-yellow color change and green fluorescence quenching. The resulting yellow solution could change to pink and regenerate to green fluorescence immediately upon the addition of sulfide anion; however, no changes were observed in the presence of other anions, including CN-, P2O74-, and other forms of sulfate, making compound L1 an extremely selective and efficient sulfide chemosensor. The signal transduction occurs via reversible formation-separation of complex L1Cu and CuS. What's more, the biological imaging study has demonstrated that the chemosensor can detect sulfur anions in biological systems at a relatively low concentration.