A ratiometric near‐infrared fluorescent probe for the detection and monitoring of hypochlorous acid in rheumatoid arthritis model and real water samples

Abstract Recent studies revealed that the increased level of hypochlorous acid (HOCl) may be deemed to be one of the signs of chronic inflammatory joint disease. Accordingly, the development of effective methods for rapid and accurate detection or monitoring of HOCl in vivo is of great significance for further understanding the role of HOCl in rheumatoid arthritis (RA). Herein, a ratiometric near‐infrared (NIR) fluorescent probe ( PTA ) was reported for the detection and monitoring of HOCl. In the presence of HOCl, the electron‐rich S atom and C=C double bond of probe PTA were oxidized in sequence, resulting in the significant hypochromatic shift and decline of absorption spectra. Simultaneously, the intramolecular charge transfer (ICT) process of PTA is inhibited, causing the intrinsic fluorescence emission of PTA shift from 680 to 550 nm. PTA ‐based test paper strips were successfully prepared and applied to determinate HOCl in actual water samples by “naked eye” colorimetric method. PTA features NIR emission, large Stokes shift (200 nm), low cytotoxicity, high sensitivity (33.9 nM), and short response time (45 s), which enable it to be successfully utilized for imaging endogenous and exogenous HOCl in living zebrafish and mice. More importantly, PTA shows remarkable effectiveness for the monitoring of HOCl‐mediated treatment response to RA. Consequently, PTA provides a new approach to further understand the role of HOCl in RA and evaluate the drug treatment efficiency of RA.