A fluorescence turn-on probe for cysteine and homocysteine based on thiol-triggered benzothiazolidine ring formation

•A coumarin-based blue fluorescent probe for sensing thiol was developed.•The probe utilizes the thiol–disulfide exchange to produce a fluorescence response to the thiol.•The probe might have application in the investigation of thiol roles in biological systems.

We synthesized a new coumarin-based probe TP, containing a disulfide moiety, to detect biothiols in cells. A fluorescence turn-on response is induced by the thiol–disulfide exchange of the probe, with subsequent intramolecular benzothiazolidine ring formation giving rise to a fluorescent product. The probe exhibits an excellent selectivity for cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) and other amino acids. The fluorescent probe also exhibits a highly sensitive fluorescence turn-on response to Cys and Hcy with detection limits of 0.8 μM for Cys and 0.5 μM for Hcy. In addition, confocal fluorescence microscopy imaging using RAW264.7 macrophages demonstrates that the probe TP could be an efficient fluorescent detector for thiols in living cells.

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