A near-infrared fluorescent probe with large Stokes shift for visualizing and monitoring mitochondrial viscosity in live cells and inflammatory tissues.

Mitochondria are cellular energy factory, having an essential role in cellular metabolism. Furthermore, abnormal changes in mitochondrial viscosity have been confirmed to be closely related to many diseases. Therefore, the development of probe that responsive to mitochondrial viscosity and its application in mitochondrial viscosity measurement is considered to be a new tool for understanding diseases. In this paper, a mitochondrial viscosity probe (DICB) with a large Stokes shift (214-253 nm) was designed and synthesized by modifying the structure of the carbazole fluorophore. The probe DICB has a favorable responsive to viscosity in the near-infrared (NIR) region (703 nm). In the water-glycerol system (0.893 cP -945 cP), the fluorescence intensity of DICB at 703 nm has a 74 times increase; in the range of 5.041 cP-856.0 cp, it has a well linear fitting relationship. Meantime, the probe has excellent sensitivity to viscosity. The probe (DICB) has been confirmed to be able to detect changes of mitochondrial viscosity in cell models induced by nystatin, carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and lipopolysaccharide (LPS); it has also been validated that DICB can be used in the process of autophagy to monitor mitochondrial viscosity. More importantly, DICB can be applied to the detection of abnormal mitochondrial viscosity in inflammatory tissues at the biological level. The outstanding characteristics of DICB for mitochondrial viscosity detection are not only of great importance to the development of viscosity probes, but also provides a universal strategy to study the relationship between inflammatory and mitochondrial viscosity.