Cholesterol induced CTAB micelle-to-vesicle phase transitions

Vesicles prepared by self-assembly of a hydrated mixture of a cationic surfactant (cetyltrimethylammonium bromide) and a lipid (cholesterol) are studied as potential nanocarriers for the delivery of active ingredients. The understanding of the mechanism of the micelle-to-vesicle transition involved in the vesicle formation appears to be crucial regarding the stability of the vesicles as nanovectors. Here, UV–Vis spectroscopy is used to monitor the phase transition from micelles to vesicles promoted by the progressive addition of cholesterol to CTAB micellar solutions. The employed solvatochromic indicator, pinacyanol chloride (PIN), is a cyanine dye that is highly sensitive to the polarity of the medium. The self-assembly between the CTAB and the cholesterol molecules is investigated by means of turbidity (optical density) measurements as well.