HYBRID BILAYER-MEMBRANES IN AIR AND WATER - INFRARED-SPECTROSCOPY ANDNEUTRON REFLECTIVITY STUDIES

In this report we describe the fabrication and characterization of a p hospholipid/alkanethiol hybrid bilayer membrane in air. The bilayer is formed by the interaction of phospholipid with the hydrophobic surfac e of a self-assembled alkanethiol monolayer on gold. We have character ized the resulting hybrid bilayer membrane in air using atomic force m icroscopy, spectroscopic ellipsometry, and reflection-absorption infra red spectroscopy. These analyses indicate that the phospholipid added is one monolayer thick, is continuous, and exhibits molecular order wh ich is similar to that observed for phospholipid/phospholipid model me mbranes. The hybrid bilayer prepared in air has also been re-introduce d to water and characterized using neutron reflectivity and impedance spectroscopy. Impedance data indicate that when moved from air to wate r, 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 scat tering from these samples was collected out to a wave vector transfer of 0.25 Angstrom(-1), and provided a sensitivity to changes in total l ayer thickness on the order of 1-2 Angstrom. The data confirm that the acyl chain region of the phospholipid layer is consistent with that o bserved for phospholipid-phospholipid bilayers, but suggest greater hy dration of the phospholipid headgroups of HBMs than has been reported in studies of lipid multilayers.