Imaging of intracellular mitochondrial membrane potential with a highly photostable NIR fluorescent probe

Mitochondrial membrane potential (ΔΨ_m) participated in important physiological processes such as ATP synthesis, ion exchange, and plays an important role in maintaining normal life activities of cells. Herein, we synthesized a fluorescent probe EDXB (3-ethyl-2-(2-(6-methoxy-2,3-dihydro-1H-xanthen-4-yl) vinyl) benzothiazol-3-ium iodide) with positive charge, which targets mitochondria by electrostatic attraction. The probe has twisted intramolecular charge transfer (TICT) characteristics, resulting in near-infrared fluorescence emission enhanced with the increase of viscosity, when the probe falls off from the mitochondrial membrane to the low-viscosity cytoplasmic aqueous phase, the fluorescence emission intensity is weakened. Therefore, the EDXB exhibited favorable targeting. In addition, EDXB also has good anti-bleaching and pH stability, which enables it to accurately feedback the change of ΔΨ_m. In the experiment, the intracellular imaging of EDXB certificated mitochondrial depolarization (decrease of ΔΨ_m) during various cell injury events including cell inflammation, apoptosis and mitophagy. We expect EDXB to be a useful tool for the analysis of ΔΨ_m changes.