A red-emissive mitochondrial probe for imaging of the viscosity in living cells

A novel water-soluble fluorescent probe L based on indole salts has been designed, synthesized and fully characterized. The systematic investigations demonstrated that probe L shows red emission and the fluorescence intensity is linear with the viscosity of the medium. Probe L is able to selectively accumulate in mitochondria within 1 min without any additional reagents for membrane permeabilization. It has been used to distinguish the viscosity differences between mitochondria in normal and nystatin-treated HeLa cells. In addition, due to the good photostability, probe L can be used to monitor the dynamics of mitochondria. These results support that probe L might provide a promising approach for the fluorescence detection of mitochondrial viscosity in living biological systems.