A highly selective and sensitive ON-OFF-ON fluorescence chemosensor for cysteine detection in endoplasmic reticulum.

A new complex between coumarin-based ligand (CL) and copper ion has been prepared and applied to be an ON-OFF-ON reversible fluorescence chemosensor for the detection of Cys with high sensitivity and specificity. In HEPES buffer, CL displayed high affinity towards Cu(2+) ion over other physiological and environmental metal ions, accompanied with a 98.4% of fluorescence quenching. In the presence of Cys, the detachment of Cu(2+) ion of CL-Cu(2+) ensemble led to the liberation of the fluorophore, CL, and thus fluorescence was recovered. The results of absorption and emission spectroscopy analyses confirmed that the fluorescence turn ON response of CL-Cu(2+) ensemble was selective towards Cys only with high sensitivity (detection of limit, 7.2×10(-7) M). Confocal microscopy studies indicated that the lipophilic CL targets the endoplasmic reticulum (ER) of live cells, where it could be functioned as a fluorescent chemosensor for visualization of Cys in this organelle. Quantitative fluorescence detection of Cys in ER was successfully realized by flow cytometry analysis. The developed chemosensor was further applied to detect Cys in real urine samples with great recoveries ranges from 95.41% to 107.40%.