A novel near-infrared ratiometric fluorescent probe targeting lysosomes for imaging HOCl in vitro and in vivo

Hypochlorous acid (HOCl), as an important biological reactive oxygen species (ROS), plays an important role in microbial immune defense and inflammatory response. Abnormal levels of HOCl in lysosomes can cause lysosomal membrane rupture and release of various hydrolases, leading to a variety of diseases, including cancer. In order to better monitor the level of HOCl in lysosomes, phenothiazine was chosen as fluorophore to construct a NIR fluorescent probe PMM with intramolecular change transfer process (ICT). PMM is a colorimetric and ratiometric fluorescent probe, which has high sensitivity with a low detection limit (20 nM), high selectivity and anti-interference. PMM has good stability in the weakly acidic environment of pH 4.0–5.5. PPM has good localization ability for lysosomes and has been successfully used for fluorescence imaging of exogenous and endogenous HOCl in HepG2 cells. Moreover, nude mouse imaging also demonstrated that PMM could be used to detect HOCl in vivo.