In Vivo NIR‐II Ratiometric Imaging of Peroxynitrite for Tracking Redox Dynamics in Tumor Immunochemotherapy

ABSTRACT Peroxynitrite (ONOO − ) is a key mediator of redox imbalance in inflammation and cancer, with in vivo monitoring of its dynamic behavior still posing a major challenge. Here, we developed a BD@PEG nanoprobe that enabled dual‐excitation NIR‐II ratiometric imaging with superior biocompatibility, quantitative fidelity, and ONOO − selectivity. When applied to a drug‐induced liver injury model, BD@PEG‐based NIR‐II ratiometric imaging allowed real‐time monitoring of hepatic ONOO − dynamics, directly correlating oxidative/nitrosative stress to histopathological alterations, and demonstrating significant attenuation under glutathione treatment. In a CT26 tumor model, the NIR‐II ratiometric imaging strategy revealed distinct ONOO − modulation in response to different therapeutic interventions. Furthermore, two‐plex imaging by integrating NIR‐IIb oxyhemoglobin saturation analysis afforded concurrent assessment of nitrosative stress and vascular oxygenation. We found that the combination of chemotherapy and immunotherapy induced synergistic ONOO − production, enhanced immune cell infiltration, and achieved superior antitumor efficacy. Overall, this study established a versatile imaging platform for dynamic redox monitoring and oxygenation assessment in vivo, providing mechanistic insight into ONOO − ‐mediated pathology and a translational tool for optimizing therapeutic interventions in cancer and inflammation.