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Direct detection of the gel-fluid phase transition of a single supported phospholipid bilayer using quartz crystal microbalance with dissipation monitoring.

Supported phospholipid bilayers (SPBs) are valuable models for fundamental studies of biological membranes and their interaction with biologically relevant solutes or particles. Herein, we demonstrate the capability of the quartz crystal microbalance with dissipation monitoring (QCM-D) to directly detect the gel-fluid phase transition of a SPB. The approach involves comparison of the frequency response of a bare and a bilayer-coated QCM-D crystal during linear temperature variation. Phase transition results in a change of the resonance frequency that coincides directly with the accompanied change in bilayer thickness detected by ellipsometry. Experiments performed at different heating rates further demonstrate the use of dissipation monitoring to determine the phase transition temperature based on the temperature-induced viscosity changes of the ambient medium in the immediate environment of the bilayer. Unlike other methods, the proposed approach enables precise determination of the phase transition of a SPB without the need for thermal equilibration of the measurement chamber and, thus, has great potential for sensitive detection of structural and/or compositional changes of the bilayer.