Design of Activatable NIR-II Molecular Probe for In Vivo Elucidation of Disease-Related Viscosity Variations

Clear elucidation of disease-related viscosity change in vivo is significant yet highly challenging as well. Fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm) has gained increasing attention for observation in living organisms, but viscosity-activatable fluorescent probe emitting at this region remains a vacancy. Herein, we report the first panel of viscosity activated NIR-II emissive fluores-cent probe WD-X. By embedding different substituents into WD-X platform and screening, we obtained an ideal probe WD-NO2 which displayed the best combination of proper-ties, including a 31-fold fluorescence enhancement in re-sponse to viscosity, insensitivity to environments (pH, po-larity) and relatively high quantum yield (1.6 % in glycerol). WD-NO2 was successfully applied to track the variation of viscosity in diabetes-induced liver injury process in vivo.