Phase transitions in lipid vesicles detected by a complementary set of methods: heat-transfer measurements, adiabatic scanning calorimetry, and dissipation-mode quartz crystal microbalance

Abstract

We report on the use of the heat transfer method, a novel surface-sensitive technique based on heat transfer through solid-liquid interfaces, to detect phase transitions of model lipid membranes. We selected the lipid DPPC because of its rich phase behavior in an experimentally accessible temperature range. The vesicles were adsorbed on nanocrystalline diamond films, known as a versatile platform material for biosensing with outstanding heat-conduction properties. Complementary Peltier-element-based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements were carried out to monitor the phase transitions in multilamellar and small unilamellar vesicles, respectively. The heat-transfer measurements revealed reversible jumps upon heating and cooling in the thermal resistance in the vicinity of the expected transition temperature and they agree qualitatively with molecular simulations of the thermal conductivity across a lipid bilayer. The results show the capability of the heat transfer method to detect the main phase transition in DPPC, opening new perspectives for the study of more complex lipid systems and different solid platforms. This work confirms QCM-D as a useful tool for the assessment of the structural changes upon the phase conversion and shows the capability of pASC to provide high-resolution thermodynamic information on biophysical systems. Temperature profile of the heat transfer resistance Rth during the main phase transition of a DPPC supported vesicle layer adsorbed on a hydrogen-terminated nanocrystalline diamond substrate. The arrows indicate the sense of the run: heating (red solid line) and cooling (blue solid line). (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim