An ESIPT-ICT synergistic near-infrared probe for selective detection of Cys in HeLa cells and zebrafish.

As a small molecule thiol, cysteine (Cys) plays a vital role in living organisms. It can stabilize the cellular redox state, maintain metabolic balance, and participate in the regulation of multiple physiological and pathological processes. Therefore, constructing fluorescent probes for the specific sensing of Cys is of great significance. In this study, by utilizing the synergistic mechanisms of excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT), we successfully synthesized a novel near-infrared fluorescent probe BIAC. This probe can specifically recognize and detect Cys. Upon excitation at 532 nm, it exhibits a maximum emission at 710 nm, and features a large Stokes shift of 178 nm. Moreover, the reaction between the probe and Cys is complete within 40 s. A good linear correlation between fluorescence intensity and Cys concentration is obtained in the range of 0-100 μM, with a limit of detection (LOD) of 0.14 μM. In addition, BIAC possesses low cytotoxicity and has been successfully utilized to detect Cys in HeLa cells and zebrafish, demonstrating its potential for bioimaging applications.