Solvent-Assisted Lipid Self-Assembly at Hydrophilic Surfaces: Factors Influencing the Formation of Supported Membranes

Abstract

As a simple and efficient technique, the solvent-assisted lipid bilayer (SALB) formation method offers a versatile approach to fabricating a planar lipid bilayer on solid supports. Corresponding mechanistic aspects and the role of various governing parameters remain, however, to be better understood. Herein, we first scrutinized the effect of lipid concentration (0.01 to 5 mg/mL) and solvent type (isopropanol, n-propanol, or ethanol) on SALB formation on silicon oxide in order to identify optimal conditions for this process. The obtained fluid-phase lipid layers on silicon oxide were investigated by using the quartz crystal microbalance with dissipation monitoring, epifluorescence microscopy, and atomic force microscopy. The experimental results indicate that, in alcohol, lipid attachment to the substrate is reversible and reaches equilibrium in accordance with the bulk lipid concentration. During the solvent-exchange step, the water fraction increases and the deposited lipids are converted into planar bilayer fragments, along with the concurrent adsorption and rupture of micelles within an optimal lipid concentration range. In addition, fluid-phase lipid bilayers were successfully formed on other substrates (e.g., chrome, indium tin oxide, and titanium oxide) that are largely intractable to conventional methods (e.g., vesicle fusion). Moreover, gel-phase lipid bilayers were fabricated as well. Depending on the phase state of the lipid bilayer during fabrication, the corresponding adlayer mass varied by approximately 20% between the fluid- and gel-phase states in a manner which is consistent with the molecular packing of lipids in the two arrangements. Taken together, our findings help to explain the mechanistic details of SALB formation, optimize the corresponding procedure, and demonstrate the general utility for fabricating gel- and fluid-phase planar lipid bilayers.