A benzothiazole-based fluorescent probe for rapid spectroscopic detection of cysteine and bioimaging in cells and zebrafish.

Cysteine (Cys) is an important low-molecular-weight biothiol whose abnormal fluctuation is closely related to redox imbalance and several disease-associated processes. Herein, we report an acrylate-functionalized benzothiazole fluorescent probe, HBT-D, for selective Cys detection and biological imaging. HBT-D showed weak fluorescence in the free state because the acrylate unit blocked the ESIPT process of the benzothiazole fluorophore. After reaction with Cys, cleavage of the acrylate moiety restored the ESIPT pathway, giving a clear turn-on emission at around 450 nm together with a visible color change from colorless to blue. Under the optimized conditions, HBT-D responded to Cys within 5 min and showed a concentration-dependent fluorescence enhancement with a detection limit of 7.51 μM. The probe displayed a preferential response to Cys over Hcy, GSH, and other biologically relevant species. HRMS analysis supported the proposed Cys-induced acrylate cleavage mechanism. Moreover, HBT-D exhibited low cytotoxicity and was successfully used for fluorescence imaging of Cys in HeLa cells and zebrafish. These results indicate that HBT-D provides a simple fluorescence method for Cys detection in biological systems.