Abstract
Fluorescence imaging technique, characterized by high sensitivity, non-invasiveness and no radiation hazard, has been widely applicated in the biomedical field. However, the depth of tissue penetration is limited in the traditional (400–700 nm) and NIR-I (the first near-infrared region, 700–900 nm) imaging, which urges researchers to explore novel bioimaging modalities with high imaging performance. Prominent progress in the second near-infrared region (NIR-II, 1000–1700 nm) has greatly promoted the development of biomedical imaging. The NIR-II fluorescence imaging significantly overcomes the strong tissue absorption, auto-fluorescence as well as photon scattering, and has deep tissue penetration, micron-level spatial resolution, and high signal-to-background ratio. NIR-II bioimaging has been regarded as the most promising in vivo fluorescence imaging technology. High brightness and biocompatible fluorescent probes are crucial important for NIR-II in vivo imaging. Herein, we focus on the recently developed NIR-II fluorescent cores and their applications in the field of biomedicine, especially in tumor delineation and image-guided surgery, vascular imaging, NIR-II-based photothermal therapy and photodynamic therapy, drug delivery. Besides, the challenges and potential future developments of NIR-II fluorescence imaging are further discussed. It is expected that our review will lay a foundation for clinical translation of NIR-II biological imaging, and inspire new ideas and more researches in this field.
Highlights
Optical imaging has the advantages of safety, no radiotoxicity, non-invasiveness, high rapid output, low detection limit and high resolution compared with other imaging modalities, such as positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound imaging
Based on the aforementioned FDA-approved indocyanine green with NIR-II tail fluorescence and its favorable results in NIR-II imaging in animal models, these findings pave the way for clinical translation of NIR-II surgical navigation
In 2019, professor Zhang reported the J-aggregates for NIR-II noninvasive dynamic vascular imaging (Figures 3A–C)
Summary
Optical imaging has the advantages of safety, no radiotoxicity, non-invasiveness, high rapid output, low detection limit and high resolution compared with other imaging modalities, such as positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound imaging The aggregation-induced emission properties of phenothiazine units were exploited to reduce the nonradiative decay paths of aggregated polymers on the one hand, and a large number of side chain groups were introduced to further enhance the fluorescence quantum yield by reducing the strong inter-chain π-π stacking interactions through spatial site resistance on the other hand (Zhang Z. et al, 2020) This dual enhancement strategy has potential applications in the design of NIR-II fluorophores for in vivo fluorescence imaging. Bai et al developed a new class of aza-BODIPY dyes: NJ960, NJ1030 and NJ1060, which can redshift the NIR emission to NIR-II These dyes have good photophysical properties, such as large Stokes shift, good photostability and high fluorescence brightness in aqueous solution. Based on the aforementioned FDA-approved indocyanine green with NIR-II tail fluorescence and its favorable results in NIR-II imaging in animal models, these findings pave the way for clinical translation of NIR-II surgical navigation
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