Fluorescent Probes for NIR-I Bioimaging

To understand the significance of biological processes in living systems, it is first necessary to unveil related phenomena, preferably visualized through the direct readout of fluorescence signals. Near-infrared (NIR)-I bioimaging enables direct and in situ observation of these biological phenomena through selective labeling of target biomolecules, subcellular organelles, and living cells, as well as malignant tissues. Since the imaging depth is greatly improved relative to fluorescence imaging in the visible region, NIR fluorescence imaging provides precise spatiotemporal information on biomolecules, particularly in vivo. One typical advance using NIR-I bioimaging technology is fluorescence image-guided tumor surgery, which has been successful in clinical trials. From a chemistry perspective, NIR-I bioimaging requires the development of fluorescent probes that can emit NIR-I fluorescence signals. In this chapter, we discuss small molecule fluorescent probes, highlighting the latest publications in the area of NIR-I bioimaging, focusing on the fundamental principles of design, synthetic protocols, and photophysical properties of NIR-I fluorophores and fluorescent probes. The future direction of bioimaging with these NIR-I fluorescent probes is also discussed.