Background: Nanoparticle imaging and tracking the release of the loaded material from the nanoparticle
system have attracted significant attention in recent years. If the release of the loaded molecules could be
monitored reliably in vivo, it would speed up the development of drug delivery systems remarkably.
Methods: Here, we test a system that uses indocyanine green (ICG) as a fluorescent agent for studying release
kinetics in vitro and in vivo from the lipid iron nanoparticle delivery system. The ICG spectral properties like its
concentration dependence, sensitivity and the fluctuation of the absorption and emission wavelengths can be
utilized for gathering information about the change of the ICG surrounding.
Results: We have found that the absorption, fluorescence, and photoacoustic spectra of ICG in lipid iron nanoparticles
differ from the spectra of ICG in pure water and plasma. We followed the ICG containing liposomal
nanoparticle uptake into squamous carcinoma cells (SCC) by fluorescence microscopy and the in vivo uptake into
SCC tumors in an orthotopic xenograft nude mouse model under a surgical microscope.
Conclusion: Absorption and emission properties of ICG in the different solvent environment, like in plasma and
human serum albumin, differ from those in aqueous solution. Photoacoustic spectral imaging confirmed a peak
shift towards longer wavelengths and an intensity increase of ICG when bound to the lipids. The SCC cells
showed that the ICG containing liposomes bind to the cell surface but are not internalized in the SCC-9 cells after
60 minutes of incubation. We also showed here that ICG containing liposomal nanoparticles can be traced under a
surgical camera in vivo in orthotopic SCC xenografts in mice.