A Rhodol-based Fluorescent Probe with a Pair of Hydrophilic and Rotatable Wings for Sensitively Monitoring Intracellular Polarity.

Cell polarity, as a vital intracellular microenvironment characteristic, has immense effects on numerous pathological and biological processes. Therefore, the tracking of polarity variations is highly essential to explore the role and mechanism of the polarity in pathophysiological processes. Herein, we designed and synthesized a novel rhodol-based fluorescent probe (RDS) sensitive to polarity by introducing a bis(2-hydroxyethylthio)methyl group, like a pair of hydrophilic and rotatable wings, into the rhodol skeleton. This unique design makes RDS adopt the colorless and non-fluorescent spirocyclic form in a low-polarity medium while the colored and fluorescent ring-open form is present in a high-polarity system, resulting in a positive-correlation response of fluorescence intension to polarity. Importantly, RDS was successfully applied to monitor the polarity changes in living cells including cancer cells, healthy cells and senescent healthy cells, visualizing that the polarity of cancer cells is lower than that of healthy cells in which the more senescent ones have higher polarity.