Recent advances in NIR-II fluorescence imaging for biomedical applications

Fluorescence imaging in the second near-infrared (NIR-II, 1000-1700 nm) spectral window has rapidly advanced as a powerful modality for biomedical research and clinical translation. Compared with visible and NIR-I techniques, NIR-II imaging offers reduced scattering, lower background autofluorescence, and deeper tissue penetration, thereby enabling high-resolution, real-time visualization of complex biological processes. In this review, we summarize the representative probe categories, including inorganic nanomaterials, organic materials, and hybrid multifunctional systems, with emphasis on their optical performance, biocompatibility, and translation potential. We highlight recent breakthroughs in biological monitoring applications, such as neural system imaging, vascular and lymphatic imaging, cell tracking, and infection diagnosis, where NIR-II imaging has provided dynamic insights unattainable by conventional methods. In addition, therapeutic integrations, including photothermal therapy, photodynamic therapy, and immunotherapy, demonstrate how NIR-II probes can serve as versatile theranostic platforms, combining precise diagnosis with targeted intervention. This review also discusses the challenges that remain in fluorophore design, biosafety, and standardization, and proposes future directions to accelerate clinical translation. By bridging fundamental optical innovations with pressing biomedical needs, NIR-II fluorescence imaging is poised to reshape precision diagnostics and therapeutic strategies in diverse disease contexts.