Phase transitions in adsorbed lipid vesicles measured using a quartz crystal microbalance with dissipation monitoring

Phase-transition induced structural changes of 1,2-ditridecanoyl-sn-glycero-3-phosphocholine (DTPC) lipid vesicles adsorbed on a titanium oxide (TiO(2)) surface have been investigated using a quartz crystal microbalance with dissipation (QCM-D) monitoring device. The frequency and energy dissipation responses obtained upon scanning the temperature across the phase-transition temperature were fitted to a Voigt-based viscoelastic model. The phase-transition induced changes of the effective viscosity and effective film thickness were used to define the phase transition temperature, explore hysteresis upon temperature sweeps with different rates and to unravel structural changes during the phase transition. To explore the influence of the vesicle-surface interaction on the phase-transition behavior, salt content and pH were varied. The results reveal less pronounced hysteresis and higher phase-transition temperatures with increasing strength of the surface interaction. The advantage of probing phase-transition induced structural changes without external labels and the validity of the Voigt-based model to represent the QCM-D response for adsorbed lipid vesicles are discussed.