Fluorescence properties of indocyanin green: I. In-vitro study with micelles and liposomes

ICG is a tricarbocyanin fluorescent dye used in angiography. Several reports point out the advantage of ICG to fluoresce in the near IR wavelength range enabling the imaging of deep tissues. If the fluorescence characteristics of ICG in buffer or protein solutions are described in vitro, little is known concerning the physicochemical properties of ICG. This study aims to evaluate the physicochemical and fluorescence spectral characteristics of ICG in aqueous solution and in presence of micelles and liposomes. ICG exhibits a tensioactive property and when incubated with micelles and liposomes tends to be aggregated or embedded at the interface. The fluorescence is very low in the aggregated form and is very high when ICG is embedded at the interface and a shift of the emission peak toward longer wavelength is observed. Such in vitro study could contribute to a better understanding of some observed unusual properties of ICG in vivo.