Formation of asymmetrical planar lipid bilayer membranes from characterized monolayers.

A device allowing the formation of lipid bilayers by apposition of characterized monolayers has been designed and constructed. It is essentially composed of two solid Teflon Langmuir troughs, pressed along one another. The troughs are both equipped with a movable barrier for the compression of the monolayers and a float-type torsion balance for the detection of the surface pressures. The lipid bilayers are formed across a tiny hole (0.225 mm diameter) punched through a polymer film clamped in between the two troughs and are characterized by their electrical properties (specific resistance and capacitance). Experimental results have been obtained on asymmetrical membranes of phosphatidylethanolamine and phosphatidylserine formed from monolayers and from lipid films many molecular dimensions in thickness. Two polymer supports, Teflon and polypropylene, were used and coated with either squalene or petroleum jelly. The results show that the stability of the bilayer, particularly when formed from monolayers, is a direct function of the interactions of the lipids with the coated support. The most stable membranes are obtained when Teflon is used as support and squalene as coating. The most important advantage of the technique presented here is found when the bilayers are formed from mixtures of components deposited at the interface. Indeed, our system allows a characterization of the miscibility of the components in the monolayers prior to form the membrane, as opposed to a complete ignorance of the molecular organization when the bilayers are formed by apposing lipid films.