Protein-Enhanced NIR-IIb Emission of Indocyanine Green for Functional Bioimaging

Abstract

Fluorescence imaging performed in the 1500−1700 nm spectral range (labeled near-infrared IIb, NIR-IIb) promises high imaging contrast and spatial resolution for its little photon scattering effect and minimum autofluorescence. Though inorganic and organic probes have been developed for NIR-IIb bioimaging, most are in the preclinical stage, hampering further clinical application. Herein, we showed that indocyanine green (ICG), a US Food and Drug Administration (FDA)-approved agent, exhibited a remarkable amount of NIR-IIb emission when dissolved into different protein solutions, including human serum albumin, rat bile, and fetal bovine serum. We performed fluorescence imaging in the NIR-IIb window to visualize structures of the lymph system, extrahepatic biliary tract, and cerebrovascular. The results demonstrated that proteins promoted NIR-IIb emission of ICG in vivo and that NIR-IIb imaging with ICG preserved a higher signal-to-background ratio and spatial resolution compared with the conventional NIR-II fluorescence imaging. Our findings confirm that NIR-IIb fluorescence imaging can be successfully performed using the clinically approved agent ICG. Further clinical application in the NIR-IIb region would hopefully be carried out with appropriate ICG−protein solutions.

NIR-II Fluorophore with Dithienylethene as an Electron Donor for Fluorescence/Photoacoustic Dual-Model Imaging and Photothermal Therapy

“…The synthesis routes of BBTD-BTE and BBTD-BTE-PEG are presented in Scheme 1. BBTD-BTE was prepared by the Suzuki reaction between 1,2-bis(5-chloro-2-methylthiophen-3yl)cyclopent-1-ene (BTE) and 4,8-dibromobenzo[1,2-c;4,5-c′]bis [1,2,5]thiadiazole (BBTD), and the two flanking aryl chlorides in BBTD-BTE were further used to incorporate poly(ethylene glycol) (PEG) chains to achieve hydrophilic modification. The characterization data of the intermediates and target compound can be found in Figures 1 and S1−S13.…”

“…In recent years, the emergence of various optical functional materials has been greatly accelerating the development of optical imaging and therapy . In the context of optical imaging, the fluorescence (FL) imaging in the second near-infrared (NIR-II) window presents great advantages compared to the visible and traditional near-infrared (NIR-I) fluorescence imaging in terms of imaging resolution, depth, and signal-to-noise ratio due to the lower tissue scattering and absorption and depressed autofluorescence in the NIR-II optical window. − As contrast agents, NIR-II fluorophores determine the quality of the fluorescence imaging. − Because the excited-state energy can be relaxed by both radiative and nonradiative decay pathways, apart from photoluminescence, NIR-II fluorophores generally possess photothermal-related functionalities, such as photoacoustic (PA) imaging and photothermal therapy (PTT). − Moreover, most NIR-II fluorophores have NIR absorption, which would further impart high performance to PA imaging and PTT thanks to the high tissue penetration of the NIR light . Compared to fluorescence imaging, the PA technique has its intrinsic advantages; for example, it has a higher imaging depth and can achieve tomographic imaging and 3D reconstruction, providing more medical information. − However, PA imaging has relatively lower sensitivity.…”

Fluorescent Tracers for In Vivo Imaging of Lymphatic Targets

“…In plasma, the absorption and emission peaks of ICG are around 807 and 822 nm (Schaafsma et al, 2011). Furthermore, the fluorescent intensity increases when ICG is mixed with fetal bovine serum (FBS) or human serum albumin (HSA) (He et al, 2020), and the quantum yield has been shown to increase by nearly 3.5 times when it is mixed with FBS (Jung et al, 2013). Mordon et al (1998) suggested that, in plasma, some ICG binds to blood endothelial cells, further increasing the maximum absorbance wavelength from 826 to 835 nm, but it is unknown if the same process occurs in lymphatic vessels.…”

“…Although ICG has an emission spectra peak in the NIR-I range, it displays a long tail that can be detected in the NIR-II and SWIR ranges using appropriate sensors. The potential benefit of doing this is the lower tissue autofluorescence and scattering, giving improved SBR, contrast, and spatial resolution, and although other NIR-II/SWIR fluorophores exist, ICG is FDA-approved (He et al, 2020;Swamy et al, 2021). Carr et al (2018) used 808 nm excitation light and an indium gallium arsenide (InGaAs) SWIR sensor (NIRvana 640, Princeton Instruments) with 1,000-1,400 nm long-pass filters to interrogate ICG after subcutaneous injection in mice hind feet and tails.…”

“…The authors concluded that NIR-I imaging is appropriate for ICG lymphangiography if the image is not contrast limited, but if it is, longer wavelengths may be useful. He et al visualized mouse lymphatics using a 1,500 nm long-pass filter and InGaAs sensor (He et al, 2020). They found that fluorescent intensity at 1,500-1,700 nm was greatly enhanced by premixing ICG with 4% HSA, compared to 0%, and that the SBR was much higher at this wavelength compared to shorter wavelengths.…”