Advances in the near-infrared Ⅱ for in vivo fluorescence imaging applications: A review

Second near-infrared (NIR-II) fluorescence imaging technology utilizes the wavelength range of 1000-1700 nm, significantly reducing tissue absorption and scattering, and combining high spatial resolution and extremely low spontaneous fluorescence, bringing a breakthrough to biomedical imaging. This review systematically explores the fundamental principles and intrinsic advantages of NIR-II optical imaging. Crucially, it delineates three strategies for probe design: achieving red-shifted emission wavelengths, modulating donor-acceptor electronic structures, and implementing synergistic metal coordination coupled with surface engineering. These approaches enable the tailored optimization of probe performance for diverse clinical applications.The review further showcases the exceptional capabilities of NIR-II imaging in structural and functional visualization across macroscopic, mesoscopic, and microscopic scales in vivo. Delving into cutting-edge applications, it critically analyzes the role of NIR-II in tumor theranostics, advanced biosensing, intraoperative navigation, and multimodal synergistic imaging. Particular emphasis is placed on the transformative potential of integrated photodynamic therapy platforms enabling a "minimally invasive, diagnosis-treatment-monitoring" closed-loop theranostic paradigm. Ultimately, this review aims to catalyze the development and clinical translation of NIR-II imaging technology, providing innovative concepts and powerful tools for biomedical research and clinical practice. It concludes by envisioning future directions focused on overcoming existing challenges through molecular engineering and technological convergence, and exploring deeper imaging windows (NIR-IIc, NIR-III).