Simple turn-on fluorescent probe for ultrafast and highly selective detection of hydrogen sulfide in aqueous solutions.

5H-Benzimidazo[1,2-c]quinazoline-6-thione (BI-QT), was synthesized as a benzimidazole-based probe to detect HS. BI-QT exhibits a fluorescent "turn-on" response in DMSO/HO (9:1, HEPES 10 mM, pH 7.4) upon the addition of HS. The BI-QT probe can determine micromolar (0-600 µM) HS concentrations in aqueous systems, with a detection limit of 1.12 µM. Interestingly, BI-QT exhibited an ultrafast response to HS, with maximum intensity achieved almost instantly when exposed to HS. BI-QT is largely unaffected by pH and responds reliably over the wide 4-11 pH range, which highlights its applicability to various physiological scenarios. UV-vis, fluorescence, and H NMR spectroscopic analyses investigated the sensing mechanism. The practicality of the probe was demonstrated using water samples and living cells.