A novel red-emission phenothiazine fluorescent protein chromophore based on oxygen‒chlorine bond (O-Cl) formation for real-time detection of hypochlorous acid in cells.

Hypochlorous acid (HOCl/ClO), a reactive oxygen species (ROS), plays an indispensable role in the human immune system. In this article, a novel red-emission phenothiazine fluorescent protein chromophore RFP-Ptz was developed for the detection of HOCl in cells. In the presence of HOCl, the fluorescence signal 610 nm rose gradually and reached its plateau with 15-fold enhancement; the fluorescence quantum yield increased from 0.01 to 0.12. The electrophilic substitution of Cl towards phenolic hydroxyl group made the probe exhibited a high selective fluorescence response with a limit of detection (LOD) of 6.76 × 10 M over other analyte species and ROS. This recognition mechanism of oxygen‒chlorine bond (O-Cl) formation has confirmed by HRMS. Finally, the RFP-Ptz can be used to response HOCl with low cytotoxicity and good biocompatibility (MTT cytotoxicity assay > 89.5%). The biocompatible RFP-Ptz was successfully applied to the fluorescence imaging of HOCl-related in SGC-7901 cells.