A highly water-soluble rhodol-based fluorescent probe for the organic-solvent independent sensing of biological hypochlorous acid

As a vital reactive oxygen species (ROS), endogenous hypochlorous acid (HOCl) deeply engaged in masses of pathophysiological processes owing to its high reactivity, thus the detection of HOCl is awfully valuable for elucidating HOCl-related pathophysiology mechanism. Despite the extensive development of outstanding HOCl fluorescent probes so far, very few of them could be applied for monitoring HOCl in the pure water system. Herein, we present a novel rhodol-based fluorescent probe 6 for the unambiguous detection of HOCl in pure water, which was effectively designed and synthesized by using the spirocyclic hydrazide group as the HOCl sensitive site and introducing two hydroxyethyl groups for obtaining high hydrophilicity into the rhodol skeleton, a unique rhodamine structure. Compared to the control compound 5 without hydrophilic groups only capable to be used in the aqueous system containing organic solvent, 6 achieves the detection of HOCl not only in the above regular system but also in pure water, indicating that the introduction of hydrophilic hydroxyethyl group is an effective and reasonable approach to achieve the broader-spectrum detection of HOCl. More importantly, different with 5, highly water-soluble 6 regardless of dissolving in the regular system or pure water system can achieve the visual monitoring of HOCl with prominent sensitivity and high spatiotemporal resolution in living HepG2 cells and zebrafish, confirming the robust imaging ability of our probe 6 to HOCl in complex biosystem.