Hybrid Bilayer Membranes in Air and Water: Infrared Spectroscopy and Neutron Reflectivity Studies

Abstract

In this report we describe the fabrication and characterization of a phospholipid/alkanethiol hybrid bilayer membrane in air. The bilayer is formed by the interaction of phospholipid with the hydrophobic surface of a self-assembled alkanethiol monolayer on gold. We have characterized the resulting hybrid bilayer membrane in air using atomic force microscopy, spectroscopic ellipsometry, and reflection-absorption infrared spectroscopy. These analyses indicate that the phospholipid added is one monolayer thick, is continuous, and exhibits molecular order which is similar to that observed for phospholipid/phospholipid model membranes. The hybrid bilayer prepared in air has also been re-introduced to water and characterized using neutron reflectivity and impedance spectroscopy. Impedance data indicate that when moved from air to water, hybrid bilayers exhibit a dielectric constant and thickness that is essentially equivalent to hybrid bilayers prepared in situ by adding phospholipid vesicles to alkanethiol monolayers in water. Neutron scattering from these samples was collected out to a wave vector transfer of 0.25 A(-1), and provided a sensitivity to changes in total layer thickness on the order of 1-2 A. The data confirm that the acyl chain region of the phospholipid layer is consistent with that observed for phospholipid-phospholipid bilayers, but suggest greater hydration of the phospholipid headgroups of HBMs than has been reported in studies of lipid multilayers.

Drug-Membrane Interactions Studied in Phospholipid Monolayers Adsorbed on Nonporous Alkylated Microspheres

“…The Langmuir-Blodgett technique 30 produced a phospholipid monolayer on the surface of gold-coated plates with covalently attached octadecyl chains. 31,32 The obtained monolayer was uniform and stable in both dry and rehydrated forms. Alkylated glass plates were used to obtain a phospholipid monolayer by vesicle fusion.…”

Visualization of membrane RNAs

“…Hybrid bilayer membranes (HBMs) were formed by applying the suspension of DOPC liposomes on the alkanethiol monolayer for 90 min to allow the reorganization of the lipid vesicles and the formation of the bilayer (Meuse et al 1998), and then the surface was washed with water. Decrease of the contact angle between this surface and the surface of a drop of water was clear, indicating the formation of a hydrophilic surface (Bain et al 1989).…”

Nanostructure of supported lipid bilayers in water

“…Variations of the index of refraction on a nanometer scale are therefore beyond reach. Synchrotron x-ray [13][14][15] and neutron [16][17][18] experiments using angstrom wavelengths do not suffer this limitation. In the following, we will highlight how synchrotron reflectometry experiments resolve structural details of SLBs.…”