Vesicle Adsorption and Phospholipid Bilayer Formation on Topographically and Chemically Nanostructured Surfaces

We have investigated the influence of combined nanoscale topography and surface chemistry on lipid vesicle adsorption and supported bilayer formation on well-controlled model surfaces. To this end, we utilized colloidal lithography to nanofabricate pitted Au-SiO2 surfaces, where the top surface and the walls of the pits consisted of silicon dioxide whereas the bottom of the pits was made of gold. The diameter and height of the pits were fixed at 107 and 25 nm, respectively. Using the quartz crystal microbalance with dissipation monitoring (QCM-D) technique and atomic force microscopy (AFM), we monitored the processes occurring upon exposure of these nanostructured surfaces to a solution of extruded unilamellar 1-palmitolyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles with a nominal diameter of 100 nm. To scrutinize the influence of surface chemistry, we studied two cases: (1) the bare gold surface at the bottom of the pits and (2) the gold passivated by biotinamidocaproyl-labeled bovine serum albumin (BBSA) prior to vesicle exposure. As in our previous work on pitted silicon dioxide surfaces, we found that the pit edges promote bilayer formation on the SiO2 surface for the vesicle size used here in both cases. Whereas in the first case we observed a slow, continuous adsorption of intact vesicles onto the gold surface at the bottom of the pits, the presence of BBSA in the second case prevented the adsorption of intact vesicles into the pits. Instead, our experimental results, together with free energy calculations for various potential membrane configurations, indicate the formation of a continuous, supported lipid bilayer that spans across the pits. These results are significantly important for various biotechnology applications utilizing patterned lipid bilayers and highlight the power of the combined QCM-D/AFM approach to study the mechanism of lipid bilayer formation on nanostructured surfaces.