Ratiometric fluorescence imaging of hypochlorous acid in living cells and zebrafish using a novel phenothiazine-fused HPQ probe

Hypochlorite (ClO−), as a typical weak acidic ROS, is mainly endogenously produced by myeloperoxidase (MPO) catalyzing hydrogen peroxide (H2O2) and chloride ion (Cl−) in leukocytes. Imbalance of hypochlorite concentration will not only cause biomolecular oxidation in organism, but also are correlated with a variety of physiological diseases. In this study, a novel ratiometric fluorescence probe PHPQ for detecting ClO- by incorporating the phenothiazine moiety into the HPQ fluorophore was designed and synthesized. The probe PHPQ was shown to be capable of selectively and sensitively monitoring ClO- in a fine ratiometric manner. It also displayed the merits of large blue-shift (98 nm), rapid response (30 s), excellent sensitivity (15 nM) and significant fluorescence ratiometric variations (253-fold). Moreover, PHPQ was successfully utilized for bioimaging exogenous/endogenous ClO- in living cells (MGC-803 and RAW264.7) and in zebrafish.