Abstract: The increasing use of indocyanine green (ICG) in tissue solders has prompted us to investigate its properties in aqueous solutions. We have measured the optical absorbance of several ICG solutions over three orders of magnitude of concentration, and have analyzed the data at several different wavelengths. Our data suggest that, first, more than one oligomeric species is present in aqueous ICG solutions (even at fairly low concentrations), and second, that rather than a dimer or trimer, the predominant oligomeric species is an n-mer where n $GREQ 4. Our experiments show that the compounds generated during photodegradation of aqueous ICG are equivalent to those produced during degradation in the absence of light. Our data also confirm that the adsorption of ICG onto human serum albumin (HSA) reduces both aggregation and degradation, but also show that HSA has a finite capacity for this effect. We have used thin-layer chromatography (TLC) to study the nature of the degradation products of ICG. The degradation process is complex, leading to the formation of at least a dozen products. !13
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