A mitochondria-targeted ratiometric fluorescent probe for rapid, sensitive and specific detection of biological SO2 derivatives in living cells

In this study, we report a ratiometric fluorescent probe ( CZBI ) for sulfur dioxide (SO 2 ) derivatives based on the conjugate of carbazole and benzo[ e ]indolium, which displays colorimetric and ratiometric fluorescence dual response to HSO 3 − . The probe can quantitatively detect HSO 3 − with high specificity, fast response (within 40   s) as well as low detection limit (10   nM). A 1,4-nucleophilic addition reaction was proposed for the sensing mechanism of this probe, which was confirmed by 1 H NMR and HR-MS spectra. Fluorescence co-localization studies demonstrated that CZBI was a specific mitochondria-targeted fluorescent probe for SO 2 derivatives with excellent cell membrane permeability . Furthermore, fluorescence imaging of HeLa cells indicated that CZBI could be used for monitoring the intrinsically generated intracellular SO 2 derivatives in living cells by ratiometric fluorescence imaging. Thus, CZBI has a great potential application for exploring the role played by SO 2 derivatives in biology.