Advancements of Second Near-Infrared Biological Window Fluorophores: Mechanism, Synthesis, and Application In Vivo

In vivo fluorescence imaging in second near-infrared biological window (NIR-II) is an emerging imaging technique in both fundamental research and clinical application. NIR-II fluorescence affords high-resolution images with increasing penetration depths due to the reduced scattering, minimal absorption, and negligible autofluorescence. In this chapter, we review the recent 10-year progress made on NIR-II fluorescence imaging in 1,000–1,700 nm NIR-II windows by summarizing an increasingly advanced NIR-II fluorophores including organic dyes and inorganic nanoparticles, with tunable emission wavelengths. The NIR-II fluorescence emission mechanism and the strategy for synthesis of high quantum yield with more biocompatible and higher photostability NIR-II fluorophores will be highlighted. In addition, we provide our perspective on the current development and bright future direction of NIR-II fluorophores development in frontier fields.