Intrinsic Near‐Infrared‐II Fluorescent Nanozymes Support High‐Resolution Imaging and Tumor Catalytic Immunotherapy

Nanozymes hold considerable promise for in vivo therapy due to their stable and versatile enzyme-mimicking activities. However, real-time tracking of their dynamics with high spatiotemporal resolution and ensuring biosafety remain challenging. Here, we report a class of single-component, metal-free autofluorescent nanozymes (AFNZs) that simultaneously exhibit ultrabright second near-infrared (NIR-II) fluorescence (FL) and potent multienzyme-like activities. By precisely controlling sulfur/nitrogen (S/N) stoichiometry during the solvothermal conversion of cyanine precursors, we developed intrinsically emissive nanozymes with high-brightness NIR-II FL (quantum yield >1.4%, maximum emission wavelength >1100 nm) among metal-free nanozyme systems, achieving a 20-fold enhancement over their precursors. The optimized AFNZs exhibit strong peroxidase (POD)-, catalase (CAT)-, and oxidase (OXD)-like activities, enabling high-contrast in vivo imaging and catalytic tumor therapy. Mechanistic studies suggest that the enhanced FL is associated with restricted intramolecular motion (RIM). These nanozymes support deep-tissue tumor imaging (∼8 mm) and high-resolution angiography (∼30 µm), substantially outperforming their precursors and the clinical contrast agent indocyanine green (ICG). Furthermore, they enable precise tumor margin identification, image-guided resection of microtumors (< 5 mm), and real-time monitoring of catalytic immunotherapy associated with autophagic flux disruption and immune activation. This work offers a stoichiometry-guided strategy for constructing intrinsically fluorescent metal-free AFNZs for image-guided catalytic therapy.