Development of NIR‐II Ratiometric Fluorescent Nanoprobe for HClO Imaging in Acute Lung Injury

Abstract Efficient and high‐contrast bioimaging of acute lung injury (ALI) is crucial for studying disease progression and enabling timely interventional treatments. However, developing bioimaging probes in the second near‐infrared (NIR‐II) window to assess ALI remains challenging. In particular, ratiometric NIR‐II probes with self‐calibration functions are rare, hindering reliable detection of information during the ALI process. Herein, through hypochlorous acid (HClO) detection, a novel lung‐targeting NIR‐II ratiometric fluorescent nanoprobe (LNRFN) is developed for in vivo ALI assessment. Specifically, LNRFN integrates the NIR‐II fluorophore RT4‐C5, which responds to HClO, and the insensitive fluorophore DAD‐LZ, which serves as an internal reference, encapsulated in polystyrene‐co‐maleic anhydride (PSMA). Photophysical property studies showed that LNRFN exhibits maximum emission wavelengths above 1000 nm under 808 and 980 nm excitation. In the presence of HClO, the maximum emission at 1018 nm, when excited at 980 nm, is rapidly quenched, whereas the emission upon 808 nm excitation remains stable. Thanks to the ratiometric signal, LNRFN reliably detected endogenous HClO in both paw edema models and cell experiments. Additionally, LNRFN effectively assessed the ALI progression by monitoring HClO levels in the NIR‐II window, benefiting from its excellent lung‐targeting ability.