Melting and interdigitation of microstructured solid supported membranes quantified by imaging ellipsometry.

The phase transition of individually addressable microstructured lipid bilayers was investigated by means of noncontact imaging ellipsometry. Two-dimensional membrane compartments were created on silicon substrates by micromolding in capillaries and the phase transition of supported dimyristoylphosphadiylcholine (DMPC) and dipentadecoylphosphatidylcholine (DiC(15)PC) membranes was determined measuring area expansion and thickness of the bilayer as a function of temperature, ethanol concentration, and cholesterol content. Apart from measuring the thermotropic behavior of DMPC on glass slides and silicon wafers, the authors were able to visualize the reversible induction of an interdigitated phase by partitioning of ethanol into the microstructured lipid bilayers. Interdigitation induced by addition of ethanol was measured as a function of cholesterol content and shifts of the main phase transition temperature T(M) of microstructured DiC(15)PC were quantified as a function of ethanol concentration. They observed that cholesterol abolishes interdigitation at higher concentrations and found a biphasic behavior of T(M) as a function of ethanol concentration in good accordance to what is known from vesicles in solution.