Tethered bilayer lipid membranes (tBLMs) were prepared by the self-assembly of thiolated lipidic anchors on gold films sputtered on Si wafers, followed by phospholipid precipitation via rapid solvent exchange. They were characterized in their in-plane structure and dielectric properties. We find that the in-plane homogeneity and resistivity of the tBLMs depends critically on a well-controlled sample environment during the rapid solvent exchange procedure. The in-plane dynamics of the systems, assessed by fluorescence correlation spectroscopy (FCS) as the diffusivity of free, labeled phospholipid dissolved in the membrane, depends on the density of the lipidic anchors in the bilayer leaflet proximal to the substrate, as well as on details of the molecular structure of the anchor lipid. In DOPC tBLMs in which tethers are laterally dilute (sparsely-tethered bilayer lipid membranes, stBLMs), measured diffusivities, D ~ 4 μm2/s, are only slightly greater than those reported in physisorbed bilayers. However, as we distinguish label diffusion in the proximal and in the distal bilayer leaflets, we observe distinct diffusivities, D ~ 2 μm2/s and ~ 7 μm2/s, respectively. The value observed in the distal leaflet is identical to that in free membranes. stBLMs completed with phytanoyl lipids (DPhyPC) show consistently lower label diffusivity than those completed with unsaturated chains (DOPC). In laterally heterogeneous bilayers, the label diffusivity varies only by a factor of ~ 2 to 4 times, indicating that the distinct regions in the bilayers do not correspond to distinct phases such as a fluid phase coexisting with a gel phase.
Citation: Soft Matter
Pub Type: Journals