Preparation of fluid tethered lipid bilayers on poly(ethylene glycol) by spin-coating

The defect-free preparation of solid-supported lipid membranes on biocompatible surfaces is a steady challenge for the investigation of model membrane interfaces. For studies in which membranes of excellent quality are required, the use of laborious Langmuir-Blodgett deposition techniques is often a necessity, especially if the support consists of a polymer interface such as poly(ethylene glycol) (PEG). In this work, we present a reliable alternative method for the preparation of a uniform and highly fluid lipid bilayer by spin-coating on top of a layer of PEG(750) covalently grafted to a silicon oxide support. Small amounts of PEG(2000)-functionalized lipids are embedded within the PEG(750) layer to serve as tethers for stabilizing the lipid bilayer upon formation. Lipid bilayer homogeneity and fluidity are assessed by quantitative fluorescence microscopy and a lipid diffusion constant of 3.1 (+/-0.3) mu m(2) s(-1) is determined. Structural investigations by synchrotron X-ray reflectivity reveal a clear separation between the lipid bilayer and the supporting PEG, without any intercalated lipid residues in the PEG layer. We detect a compression of the PEG layer when the temperature is increased from 23 degrees C to 50 degrees C, which we ascribe to a release of similar to 36% of bound water molecules per PEG. The compression of the supporting PEG does not affect the lipid bilayer structure. The remarkable ability of PEG to reversibly change its level of hydration in a confined environment offers the possibility of tuning the surface properties of the PEG layer even after the deposition of the lipid membrane.