Red-emitting fluorescence probe for sensing viscosity in living cells

In this paper, we developed a red-emitting fluorescent probe TPSN based on triphenylamine-functionalized benzothiazole salts. TPSN exhibits a strong luminescence emission at about 637 nm in viscous media. Moreover, the fluorescence intensity of TPSN enhances approximately 94-fold from water to 99% glycerol. Cell imaging experiments reveals that TPSN presents high specificity for mitochondrial localization. The related mechanism study indicates that the localization property of TPSN is independent of the mitochondrial membrane potential. As a result, TPSN offers a promising tool to monitor the mitochondria viscosity in living cells.