Highly sensitive fluorescent probe based on a novel phenothiazine dye for detection of thiophenols in real water samples and living cells.

Based on an excited-state intramolecular proton transfer (ESIPT) fluorophore, a novel fluorescent off-on probe for detection of thiophenols was designed and synthesized. This probe (λex  = 401 nm, λem  = 527 nm) displayed high specificity for sensing thiophenols over other biologically related species. Besides, this probe possessed capabilities of monitoring thiophenols with rapid response rate (3 min), a large Stokes shift (126 nm), and high sensitivity (2.7 nM). The sensing mechanism was considered to be that thiophenols triggered thiolysis of the probe and the ESIPT fluorophore was released, as confirmed by means of HPLC and HRMS. Most notably, this probe was successfully applied to monitor levels of thiophenols in realistic samples and MDA-MB-231 cells. Graphical abstract A novel phenothiazine-based fluorescent probe was developed for sensitively sensing thiophenols in both aqueous medium and living cells.