A simple chalcone molecular rotor for specific fluorescence imaging of mitochondrial viscosity changes in living cells

Mitochondrial viscosity is related to numerous physiological processes such as solute diffusion, enzyme catalysis, protein folding, translocation, and conformation change. It is significant to evaluate and monitor the mitochondrial viscosity changes in living cells. In this work, we developed a simple chalcone molecular rotor MitoHCA for specific fluorescence imaging of mitochondrial viscosity changes in living cells. The chalcone molecular rotor Mito-HCA consists of a donor-pi-acceptor (D-pi-A) chalcone skeleton with a typical twisted intramolecular charge transfer (TICT) feature and a triphenylphosphonium unit for mitochondrial targeting. The fluorescent intensity and fluorescence lifetime of the probe Mito-HCA reveal good sensitivity and high selectivity to solution viscosity. It can be conveniently used for the specific fluorescence imaging of mitochondria and mitochondrial viscosity detection benefit from the simple synthetic procedure, large Stokes shift, high pH stability and low cytotoxicity. The fluorescent intensity and fluorescence lifetime of probe Mito-HCA exhibits good sensitivity to mitochondrial viscosity changes in living cells under osmotic shock, starvation stress and ionophore (monensin) incubation.