Multifunctional 1,3-benzoxazole-merocyanine-based probe for the ratiometric fluorescence detection of pH/HSO3−/viscosity in mitochondria

pH, HSO3−, and viscosity are crucial bio-markers for evaluating the status of mitochondria in the cell micro-environment. With this research, we developed a ratiometric mitochondria-targeting fluorescent probe 1 that was responsive toward bisulphite, pH and viscosity. Hydroxylphenyl 1,3-benzoxazole (D) acted as a pH recognition unit; benzo[e]indolium (A) acted as a fluorescent rotor to achieve a viscosity response; the C = C bond constructed by bridging D and A was susceptible to nucleophilic attack and hence responded to HSO3−. Probe 1 exhibits significant ratiometric signal changes, high sensitivity, outstanding selectivity, and good stability for detecting pH, viscosity, and SO2 in solution. Probe 1 was used for imaging pH, viscosity, and SO2 derivatives in live cells and zebrafish, indicating its potential for identifying mitochondrial dysfunctions.