A simple benzothiazole-based mitochondrial-targeting fluorescent probe for visualizing and monitoring viscosity in living cell, lung organ tissue, and living mice

The irregular cellular viscosity is associated with disease and malfunction at the cellular level, developing simple but effective fluorescence probe for detection of intracellular viscosity is of great significance. Herein, we report a benzothiazole-based fluorescent probe HBTD-V for sensitive response to viscosity change in biological systems. HBTD-V displays weak emission in low-viscosity media but strong fluorescence in high-viscosity media. Linear fitting of the viscosity titration results provided a good linear relationship between the fluorescence intensity (logI583) and viscosity (logη) within the viscosity range of 13.8–221.5 cp, indicating the capability of the probe for quantitative viscosity detection. Probe HBTD-V also holds some advantages such as excellent photostability, good anti-interference ability, and good mitochondrial targeting ability. Moreover, probe HBTD-V has been successfully employed to image the viscosity variations in living MCF-7 cells, mice lung organ and tissues, as well as in living mice body. The results demonstrate that HBTD-V can serve as a sensitive fluorescence probe for investigating the vital role of viscosity changes in complex biological systems.