Recent Advances in NIR-II Materials for Biomedical Applications

ConspectusOptical biomedical imaging offers unparalleled advantages in biological research, enabling precise visualization of physiological and pathological processes with exceptional sensitivity and specificity. Its noninvasive nature, high signal-to-noise ratio (SNR), and the ability to target specific molecules make it an indispensable tool for studying dynamic events within living organisms. This technology advances our understanding of life processes, provides crucial insights into disease mechanisms, and fosters breakthroughs in both medicine and biological sciences. Recently, the newly developed fluorescence imaging in the second near-infrared (NIR-II, 1000–1700 nm) window represents a significant advancement in biomedical imaging, which offers distinct advantages, such as deeper tissue penetration and higher spatiotemporal resolution over conventional imaging techniques in the well-established visible and traditional near-infrared (400–900 nm) region, resulting in clearer and more detailed images of biological structures and processes. Moreover, NIR-II fluorescence imaging exhibits minimal background interference, enhancing sensitivity and specificity in detecting molecular targets. These characteristics make NIR-II fluorescence imaging a promising tool for various biomedical applications, including tumor detection, drug delivery monitoring, and in vivo imaging of biological processes. Its potential to provide high-resolution, real-time imaging with improved sensitivity holds great promise for advancing both basic research and clinical diagnostics in the field of biomedicine. Up to now, functional NIR-II materials including small molecular dyes, polymers, single-walled carbon nanotubes, quantum dots, lanthanide nanoparticles, and coordination complex have gradually enriched the toolbox for high performance in vivo visualization of physiological structures and abnormal diseases. Although the diverse NIR-II materials differ in component, size, and surface, their optical properties confer them with multifunctional capability from imaging, sensing to phototheranostics.In this Account, we highlight the recent contributions of our research group in utilizing NIR-II materials for enhanced biomedical performance. First, we summarize our efforts on the repurposing of commercially available NIR dyes for NIR-II imaging using their emission tail. Protein and fragments further shield the dyes for improved imaging performance and adjustable pharmacokinetics. Then, we discuss the application of the contrast agent in image-guided tumor precision surgery. After that, we present a series of responsive NIR-II materials for real-time visualization of in vivo tumor microenvironment before and after therapy. We also conclude the NIR-II materials with photon energy conversion capability for phototheranostics. Finally, we propose an outlook on the possible issues and future development of this field for improved biomedical applications. We hope this Account can update the understanding of recently developed multifunctional NIR-II materials, providing some references, and promoting more adoption to accelerate the development of material science and biomedical applications.