Rational Design of Near-Infrared Fluorescent Probes for Accurately Tracking Lysosomal Viscosity with Allyl Snchoring Si-Rhodamine.

The abnormal microenvironment parameter, viscosity, is closely connected with various diffusion processes, signal transduction, molecule interactions, and various diseases. It is greatly significant to design viscosity-dependent near-infrared (NIR) small molecule fluorescence probes for visualizing biological processes or diagnosing diseases. Herein, through the stepwise modulating structure of the silicon-rhodamine fluorophore (SR), we report three viscosity probes with allyl or methyl group as rotors, named SR-T-Al, SR-S-Al, and SR-T-Me. Among them, SR-T-Al demonstrates better viscosity responsibility from 1.0 to 1410.4 cP of viscosity. Therefore, the probe of SR-T-Al is successfully applied to sensitively monitor lysosome microscopic viscosity changes of living cells induced by oxygen stress. What's more, based on its advantages in NIR emission (669 nm) and large Stokes shift (201 nm), we also use it to image variations of viscosity in an acute hepatitis mouse induced by carbon tetrachloride. Both time and concentration-dependent induction models display the great ability of SR-T-Al to detect viscosity alteration. All the experimental results indicated that this allyl-rotor-based NIR viscosity probe could provide a general platform to monitor abnormal physiological processes and diseases relating to viscosity.