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Leung K1.


Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2009 Apr 28 [updated 2009 Jun 05].

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National Center for Biotechnology Information, NLM, NIH


Optical fluorescence imaging is increasingly used to obtain biological functions of specific targets (1, 2). However, the intrinsic fluorescence of biomolecules poses a problem when fluorophores that absorb visible light (350–700 nm) are used. Near-infrared (NIR) fluorescence (700–1,000 nm) detection avoids the background fluorescence interference of natural biomolecules, providing a high contrast between target and background tissues. NIR fluorophores have wider dynamic range and minimal background as a result of reduced scattering compared with visible fluorescence detection. They also have high sensitivity, resulting from low infrared background, and high extinction coefficients, which provide high quantum yields. The NIR region is also compatible with solid-state optical components, such as diode lasers and silicon detectors. NIR fluorescence imaging is becoming a non-invasive alternative to radionuclide imaging. E-selectin is found on the cell surface of endothelial cells (3, 4). It binds to the carbohydrate moiety Sialyl-Lewisx (SLX) on the cell surface of leukocytes. Tumor necrosis factor α and interleukin-1, released as a result of inflammatory stimuli, upregulate E-selectin and other adhesion molecule expression on the vascular endothelial cells, leading to leukocyte adhesion to the activated endothelium. E-selectin and other selectins are involved in arresting leukocytes on the endothelium. Hirai et al. (5) have developed liposomes containing SLX tetrasaccharides and Cy5.5-conjugated human serum albumin (SLX-Lipo-Cy5.5) for noninvasive magnetic resonance imaging of E-selectin expression in inflammation and tumor tissue. Cy5.5 is a NIR fluorescence dye with an absorbance maximum at 675 nm and an emission maximum at 694 nm with a high extinction coefficient of 250,000 M-1cm-1.

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