Viscosity activated NIR fluorescent probe for visualizing mitochondrial viscosity dynamic and fatty liver mice

Intracellular viscosity plays an important role for maintaining the diffusion, transportation, signal transmission and cell metabolism between biomolecules. And abnormal intracellular viscosity would cause various concurrent diseases such as fatty liver, hyperlipidemia and so on. However, as far as we know, there are quite few tools could be used for imaing of intracellular viscosity, much less in-depth investigation of the viscosity-related dysfunc-tional and disease. Herein, we have designed and developed a series of NIR fluorescent probes, in which the chemical bond between fluorophore and molecular rotor was designed with single bonds, double bonds, and extended double bonds, respectively. According to the theoretical calculations and experiments results, BP-III with was selected as the most sensitive fluorescence sensor for imaging viscosity change in vitro and in vivo. As the viscosity increasesd, the TICT (twisted intramolecular charge transfer) of BP-III was inhibited, accompanied with a strong red fluorescence enhancement at 740 nm. In addition, BP-III showed excellent mitochondrial target ability and can be used to imaging viscosity changes in mitochondrial of living cells. More importantly, the probe has been used for imaging the abnormal viscosity of fatty liver at the organ level. We expect this work would provide meaningful tool for promoting fundamental research in biological viscous environment and mitochondrial viscosity related diseases.