Mesoporous supported lipid bilayers

Licentiatavhandling, 2011

Abstract Lipid bilayers are commonly used as simplified model systems of living cell membranes. They have shown to be important components in the development of biosensing devices where the bilayer acts as a host for transmembrane proteins, such as ion channels, that are utilized as sensing elements. A successful design of a biosensor device must provide membrane durability in terms of mechanical stress and chemical stability and simultaneously provide a suitable environment for proteins having retained function. In particular it is important to avoid unfavorable interactions between the membrane proteins and the support. In this context, mesoporous materials are promising as supports for the lipid bilayer. The pores of the material are suggested to provide an adequate environment for proteins and the walls between the pores to provide stability to the bilayer. The aim of this thesis was to investigate the possibility of using mesoporous materials as supports for lipid bilayers. The interaction between lipid bilayers and mesoporous silica and titania using quartz crystal microbalance with dissipation monitoring (QCM-D), fluorescence recovery after photobleaching (FRAP) and atomic force microscopy (AFM) has been investigated. Furthermore, the possibility of tethering lipid bilayers via covalent bonds to amine-modified mesoporous silica surfaces was investigated by the use of molecules that acted as spacers between the bilayer and the support, creating extra space between the bilayer and the support. The supported lipid bilayers were formed using vesicle fusion when adsorbed on the support. The results showed that lipid bilayers were successfully formed on mesoporous silica and that intact vesicle adsorption was obtained on titania, regardless of porosity. Mesoporous silica films having defined pore sizes of 2, 4 and 6 nm were formed and evaluated. It was shown that the formation kinetics of the lipid bilayers was dependent on the pore size with the most rapid formation on the support having the smallest pores and slowing down of the process with increasing pore size. The results were suggested to be due to the hydrophilicity of the surface, which was highest on the surface having the smallest pores and decreased with increasing pore size. Tethered lipid bilayers on amine-modified mesoporous silica were, however, difficult to form and resulted in that vesicles adsorbed intact on the surface instead of forming tethered lipid bilayers. Based upon the results, mesoporous silica is considered to be a promising support for lipid bilayers in biosensing devices, however, more studies need be performed to evaluate the possibility of covalently bind the bilayers to the support.