Glutathione functionalized copper nanoclusters as a fluorescence platform for specific biosensing of cysteine and application in cellular imaging

Herein, we have investigated a highly specific and very sensitive quantification of L-Cysteine (Cys) in human urine samples using highly fluorescent glutathione decorated copper nanoclusters (GSH-CuNCs) as a fluorescence probe. GSH-CuNCs exhibits emission peak at 613 nm with an excitation wavelength of 380 nm. Emission intensity of GSH-CuNCs was reduced after the addition of Cys. We expected that the quenching of emission intensity is due to the metal-thiol interaction between the GSH-CuNCs surface and thiol group contains the Cys analyte. Cys stimulated Cu-thiol interactions were verified by FT-IR and natural bond orbital (NBO) theory. The good linearity was achieved in the range from 3.00 × 10−8 to 42.00 × 10−8 mol dm−3 and the lowest limit of detection (LOD) was calculated as 8.63 × 10−9 mol dm−3 (S/N = 3). The effect of various potential coexistence substances such as other amino acids, metal ions and some biological relevant chemicals to GSH-CuNCs has also been investigated. Furthermore, it was found that even 10-fold higher concentrations of other thiol containing amino acids did not interfering the detection of Cys. In addition, the proposed strategies were successfully applied for the quantification of Cys in human urine samples and live cell imaging.