Fluorescence properties of indocyanin green .2. In vitro study related to in vivo behavior.

The fluorometric properties of indocyanin green has been largely described. Salts, proteins, lipoproteins are mentioned as modifying the fluorescence characteristics of ICG. We have recently observed that ICG is able to be bound at the interface of model membranes. In this study, we reinvestigated the spectral properties of ICG in biological media. The fluorescence quenching curves of ICG in the water, protein solution and whole blood are very similar but the absorption characteristics of ICG are quite different from one medium to another. ICG displays an aggregative behavior in water and serum depending on its concentration but we observed no modification of the absorption spectra in blood. This quenching property is also observed in vivo using blood sampling. These results show that the spectral behavior of ICG in biological media may be taken in account when fluorescence measurements are performed.