Investigating lyophilization of lipid nanocapsules with fluorescence correlation spectroscopy

This paper describes characterization of lyophilized lipid nanocapsules loaded with Alexa 488 by fluorescence correlation spectroscopy (FCS). Fluorimetry analysis of nanocapsules containing self-quenching concentrations of 5- and 6-carboxyfluorescein was performed to establish a point of reference for FCS. FCS results complemented the results obtained by fluorimetry for a bulk nanocapsule solution and provided additional information about the size and dye retention by individual nanocapsules. Using this method, we determined that nanocapsules composed of the thiol-functionalized lipids showed the best dye retention and the most consistent results. Dye retention, size, and photolysis efficiency of these thiol-functionalized nanocapsules doped with a far-red photosensitizer did not change substantially upon lyophilization and storage at -20 degrees C for up to 2 months, making lyophilization a suitable method for the long-term storage of nanocapsules with the appropriate lipid composition.