A reversible fluorescence chemosensor for sequentially quantitative monitoring copper and sulfide in living cells.

Abstract We report a novel, selective and sensitive strategy for the sequentially “ON–OFF–ON” fluorescent detection of Cu 2+ and S 2− based on a fluorescein derivative, FL. The specific binding of FL towards Cu 2+ in aqueous and biological media led to the intensive green fluorescence quenching and a notable increase of the absorbance maximum at 480 nm. In the presence of S 2− , the intensity and overall pattern of the fluorescence emission and UV–vis spectra of FL–Cu 2+ ensemble were recovered since the abolishment of paramagnetic Cu 2+ . This displacement approach exhibited highly specificity, and sensitivity with detection limits of 3 nM for Cu 2+ and 150 nM for S 2− . The fluorescence “ON–OFF–ON” circle can be repeated to a minimum of 5 times by the alternative addition of Cu 2+ and S 2− , implying that FL is a renewable dual-functional chemosensor. The biocompatibility of FL toward breast carcinoma cells, MDA-MB-231 was confirmed by MTT assay. The reversible “ON–OFF–ON” fluorescent response of FL to Cu 2+ and S 2− in living system was further confirmed by confocal fluorescence imaging of living cells. The quantification of Cu 2+ and S 2− in single intact cell was realized by the flow cytometry analysis.