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Indocyanine green (ICG) is a tricarbocyanine dye with good water solubility and molecular weight of 775. ICG can almost completely bind to plasma protein in plasma and whole blood, and has almost no toxic and side effects in vivo. As a functional dye molecule, ICG has unique photophysical and photochemical characteristics.
Characteristics of ICG Dyes
ICG is a three-carbon cyanine dye with near-infrared characteristic absorption peak. Different from Cy3, Cy5 and Cy 7 cyanine dyes, ICG has higher absorption and emission wavelength. The maximum emission wavelength is between 795 ~ 845 nm, ICG binds to red blood cells better than Cy 7, and has the characteristics of amphiphilic structure, both hydrophilic and lipophilic. The penetration depth of near-infrared light in tissue is large, and it is less affected by the background of biological tissue. Because ICG has the characteristics of near-infrared absorption and fluorescence emission, it can be used as an excellent tissue penetrating agent in vivo. Indocyanine green is also a negatively charged polyacetylene dye, which can combine with protein to form a non-covalent fluorescent complex. This "pseudo fluorescent" characteristic is used for protein determination by capillary electrophoresis and semiconductor laser-induced fluorescence detection.
Application of ICG Dyes
- At present, ICG is mainly used in clinical auxiliary diagnosis of liver function, cardiac output, retinal and choroidal vascular system, such as liver cirrhosis, toxic liver disease, liver fibrosis, tenacious hepatitis and other liver diseases. It can also be used to detect the reserve function of the liver and judge the degree of liver damage.
- In addition, ICG can be used as choroidal angiography agent to determine the location of choroidal diseases. With the development of science and technology, researchers use ICG as a fluorescent probe to realize real-time fluorescence imaging during surgery.
- The photothermal properties of ICG are found and utilized to make it absorb near-infrared light and convert it into heat energy or produce singlet oxygen, destroy tumor cells and realize photothermal treatment of tumors. However, the instability of ICG in aqueous solution, the rapid clearance rate in blood circulation and the lack of tumor cell targeting seriously limit its application in tumor diagnosis and treatment. Therefore, in recent years, researchers have designed and synthesized a variety of nano carriers to carry ICG in order to improve its stability, prolong blood circulation time and give it tumor targeting.