A mitochondria-specific NIR fluorescence probe for dual-detection of sulfur dioxide and viscosity in living cells and mice.

The level of sulfur dioxide (SO 2 ) and viscosity in mitochondria play vital roles in various physiological and pathological processes. Abnormalities in mitochondrial SO 2 and viscosity are closely associated with numerous biological diseases. It is of great significance to develop novel fluorescence probes for simultaneous detection of SO 2 and viscosity within mitochondria. Herein, we have developed a water-soluble, mitochondrial-targeted and near-infrared fluorescent probe, CMBT, for the simultaneous detection of SO 2 and viscosity. The probe CMBT incorporates benzothiazolium salt as a mitochondrial targeting moiety and 7-diethylaminocoumarin as a rotor for viscosity detection, respectively. Based on the prompt reaction between nucleophilic HSO 3 - /SO 3 2- and the backbone of the benzothiazolium salt derivative, probe CMBT displayed high sensitivity and selectivity toward SO 2 with a limit of detection as low as 0.17 μM. As viscosity increased, the twisted intramolecular charge transfer (TICT) process was restricted, resulting in fluorescence emission enhancement at 690 nm. Moreover, probe CMBT demonstrated exceptional mitochondrial targeting ability and was successfully employed to image variations of SO 2 and viscosity in living cells and mice. The work highlights the great potential of the probe as a convenient tool for revealing the relationship between SO 2 and viscosity in biological systems.