A red-emitting fluorescent probe for mitochondria-target microviscosity in living cells and blood viscosity detection in hyperglycemia mice

Abnormal mitochondrial viscosity is associated with many diseases and cellular dysfunctions, necessitating the development of tools to accurately measure changes in mitochondrial viscosity in living cells. Herein, we reported a new red-emitting viscosity sensor NV constructed by linking naphthalimide and benzo[e]indolium via a C-C double bond, which displayed strong fluorescence emission at 635 nm in highly-viscous medium. Furthermore, the fluorescence intensity increased by 106-fold and the quantum yield increased by 69-fold in 95% glycerol. The probe can be used to visualize changes in intracellular viscosity and monitor mitochondrial viscosity changes induced by chemical compounds or drugs. Inflammation and hyperglycemia increase intracellular viscosity and probe NV exhibited two-fold fluorescence enhancement in the fresh blood of hyperglycemia mice over that of normal mice. Taken together, probe NV could provide a powerful tool for disease diagnoses related to changes in blood viscosity.