Highly specific monitoring and imaging of endogenous and exogenous cysteine in living cells.

Cys is one of the important biothiols and its abnormal concentration may pose a threat to human health. Therefore, the monitoring of Cys in organisms is of great significance. GSH and Hcy, as the other two biothiols, have similar chemical structures and active sites to Cys. Consequently, developing fluorescent probes to independently detect Cys has become a challenging problem. Keeping this in mind, α-β unsaturated ketone as a recognition group was integrated into the coumarin group skeleton to synthesize a fluorescent probe SC. After the nucleophilic addition reaction of Cys with SC, the conjugated system of SC was blocked and the fluorescent enhanced obviously. SC was able to detect Cys specifically under the same excitation with a low detection limit (11.1 nM). SC showed a rapid respond to Cys (120 s) and good fluorescent stability over a wide pH range. In addition, it achieved extracorporeal circulation in the presence of HO or NEM. In the end, SC could be applied to detecting endogenous and exogenous Cys under biological condition due to its slight cytotoxicity and good biocompatibility. This provided a powerful tool for studying the physiological function of Cys exclusively.