A Copper (II) Ensemble-Based Fluorescence Chemosensor and Its Application in the ‘Naked–Eye’ Detection of Biothiols in Human Urine

Quick and effective detection of biothiols in biological fluids has gained increasing attention due to its vital biological functions. In this paper, a novel reversible fluorescence chemosensor (L-Cu(2+)) based on a benzocoumarin-Cu(2+) ensemble has been developed for the detection of biothiols (Cys, Hcy and GSH) in human urine. The chemosensing ensemble (L-Cu(2+)) contains a 2:1 stoichiometry structure between fluorescent ligand L and paramagnetic Cu(2+). L was found to exclusively bond with Cu(2+) ions accompanied with a dramatic fluorescence quenching maximum at 443 nm and an increase of an absorbance band centered at 378 nm. Then, the in situ generated fluorescence sluggish ensemble, L-Cu(2+), was successfully used as a chemosensor for the detection of biothiols with a fluorescence “OFF-ON” response modality. Upon the addition of biothiols, the decomplexation of L-Cu(2+) led to the liberation of the fluorescent ligand, L, resulting in the recovery of fluorescence and absorbance spectra. Studies revealed that L-Cu(2+) possesses simple synthesis, excellent stability, high sensitivity, reliability at a broad pH range and desired renewability (at least 5 times). The practical application of L-Cu(2+) was then demonstrated by the detection of biothiols in human urine sample.