We report a novel, selective and sensitive strategy for the sequentially "ON-OFF-ON" fluorescent detection of Cu2+ and S2- based on a fluorescein derivative, FL. The specific binding of FL towards Cu2+ 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 S2-, the intensity and overall pattern of the fluorescence emission and UV-vis spectra of FL-Cu2+ ensemble were recovered since the abolishment of paramagnetic Cu2+. This displacement approach exhibited highly specificity, and sensitivity with detection limits of 3 nM for Cu2+ and 150 nM for S2-. The fluorescence "ON-OFF-ON" circle can be repeated to a minimum of 5 times by the alternative addition of Cu2+ and S2-, 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 Cu2+ and S2- in living system was further confirmed by confocal fluorescence imaging of living cells. The quantification of Cu2+ and S2- in single intact cell was realized by the flow cytometry analysis.
- Dual-functional chemosensor
- Fluorescence imaging