Near-Infrared Fluorescence Imaging in Biomedicine

Near-infrared (NIR) light, spanning 700-1700 nm, has attracted increasing attention in biomedical research because of its reduced photon scattering, lower tissue absorption, and minimal autofluorescence. As a result, NIR illumination enables deeper tissue penetration while maintaining low phototoxicity, making it particularly suitable for non-invasive imaging, biosensing, and remotely triggered therapeutic interventions. However, the practical use of these optical advantages depends powerfully on how efficiently light-matter interactions can be translated into controlled biological responses. In this regard, advances in nanomaterials have played a central role. Recent developments in polymeric nanocarriers, hybrid nanoparticles, and light-responsive soft materials have enabled NIR stimulation to be converted into localized thermal effects, chemical reactions, or imaging signals. Importantly, materials design at the nanoscale governs key parameters such as stability, drug release behavior, targeting efficiency, and biological compatibility. Consequently, material choice and engineering strategies have become decisive factors in determining system performance. Despite supporting progress, numerous NIR-based nanoplatforms remain limited to pre-clinical demonstrations. Challenges interlinked to immune interactions, biodistribution, material degradation, and scalable fabrication continue to restrict broader implementation. In this review, we present a materials-focused perspective on NIR-responsive nanotechnology. We first discuss the basic photophysical principles underlying NIR activation, then analyze polymer-based carrier designs and stimulus-controlled release mechanisms. Current applications in cancer theranostics, neuroregeneration, and biosensing are critically evaluated, with attention given to both advantages and limitations. Finally, emerging design strategies aimed at improving precision, safety, and translational feasibility are highlighted, providing realistic guidance for the future development of application-ready NIR nanomedicine.