Formation of model lipid bilayers at the silica-water interface by co-adsorption with non-ionic dodecyl maltoside surfactant

This present article describes a new and simple method for preparing model lipid bilayers. Stable and reproducible surface layers were produced at sil ica surfaces by co-adsorbing lipid with surfactant at the silica surface fr om mixed micellar solutions. The adsorption was followed in situ by use of ellipsometry. The mixed micellar solution consisted of a lipid (L-alpha-dio leoyllecithin) and a non-ionic sugar-based surfactant (n-dodecyl-beta-malto side). The latter showed, by itself no affinity for the surface and could, therefore, easily be rinsed off the surface after the adsorption step. By f irst adsorbing from solutions with high lipid and surfactant concentrations and then, in succession, rinsing and re-adsorbing from solutions with lowe r lipid-surfactant concentrations, a dense-packed lipid bilayer was produce d at the silica surface. The same result can be achieved in a one-step proc ess where the rinsing, after adsorption from the concentrated solution, is performed very slowly. The thickness of the adsorbed lecithin bilayer after this treatment found was to be about 44 +/- 3 Angstrom. having a mean refr active index of 1.480 +/- 0.004. The calculated surface excess of lipids on silica was about 4.2 mg m(-2), giving an average area per lipid molecule i n the two layers of 62 +/- 3 Angstrom(2). The physical characteristic of th e adsorbed bilayer is in good agreement with previously reported data on bu lk and surface supported lipid bilayers. However, in contrast to previous i nvestigations, we found no support for the presence of a thicker multi-mole cular water layer located between the lipid layer and the solid substrate.