Near-Infrared-II Fluorescence Imaging of Tumors with Organic Small-Molecule Fluorophores

Over the past decade, near-infrared-II (NIR-II, 1000-1700 nm) fluorescence imaging has become a focal point in tumor imaging due to its advantages of low light scattering, weak biological autofluorescence, extraordinary penetration depth, high signal-to-background ratio, and micron-level high resolution. To date, a large number of NIR-II materials have been developed for tumor imaging. Among them, NIR-II organic small-molecule fluorophores have emerged as research hotspots owing to their distinctive advantages, such as superior optical properties, excellent controllability, favorable biocompatibility, and tunable pharmacokinetics. In this review, we summarize the latest progress in lNIR-II fluorescent probes based on organic small-molecule fluorophores for tumor imaging, focusing on their structural features, design principles of NIR-II fluorescent probes, and applications in tumor imaging. Finally, we will discuss the challenges, future prospects, and development directions of organic small-molecule fluorophores for NIR-II fluorescence imaging of tumors.