Mitochondria-targeting fluorescent probe with a pH/viscosity response for assisted detection of non-alcoholic fatty liver in mice†

Cancer cells are characterized by high viscosity, low pH and high levels of reactive oxygen species. Both pH and viscosity are key indicators which can respond to the microenvironment of cancer cells and are also important indicators for monitoring fatty liver. Based on this, we have constructed a hemicarbocyanine fluorescent probe (HTC) possessing a D–D′(π)–π–A structure using phenol as an electron donor (D), a thiophene moiety as an electron donor and a partial π bridge. The fluorescent probe HTC exhibits pH-responsive properties, and the fluorescence intensity of the probe at 627 nm gradually decreases and the fluorescence at 720 nm gradually increases with the increase of pH for pH = 7 to 10.5. Meanwhile, with an increase of viscosity the fluorescent probe HTC exhibited gradually enhanced fluorescence at 627 nm, thus revealing a response to the change of viscosity. In addition, the fluorescent probe HTC can target mitochondria for cellular fluorescence imaging, and co-localized fluorescence imaging with the commercial mitochondrial probe Mito-Tracker Green with a Pearson's coefficient of 0.91. We have utilized the properties of the fluorescent probe HTC, which exhibits a pH and viscosity response, and have applied it to monitor the change of pH or viscosity in cells and differentiate between normal and cancerous cells, as well as for the identification of non-alcoholic fatty liver mice. In addition, the probe is easily metabolized in mice and has good biocompatibility.