Self-assembled bio-membranes as a new material for biomolecular electronics

Using a nanoelectrospray ion source as a vapour deposition device, it has been possible to synthesise an environment in which large, transportable lipid bilayer membranes with integrated membrane proteins can assemble. Homogeneous membranes 3 mm in diameter were produced by integrating the monomolecular pore protein outer membrane porin G (OmpG) and the non-covalent trimer bacteriorhodopsin. Under these conditions, the large non-covalent 30 mer protein pore complex from listeriolysin O was able to form and insert itself into a membrane. Self-assembly occurs upon detergent extraction in a thin layer of glycerol formed on the liquid surface of a buffer solution in a small vessel. A layered environment was created by spraying different materials in several successive steps, with pauses inserted where self-assembly was required. First, a sufficient amount of phosphatidylcholine is sprayed onto the liquid surface of a buffer to generate a lipid bilayer. After several hours of assembly time, a thin glycerol layer is added to create a hydrophilic base. Then, enough phosphatidylcholine is added to enable the formation of a lipid monolayer. The next layer incorporates detergent-solubilised protein and additional lipids to enable the formation of a lipid bilayer with integrated proteins upon detergent extraction. Finally, another glycerol layer is added to complete the hydrophilic environment. The layered structure is then incubated for several days to allow the detergent to be extracted from the surface using SM-2 Biobeads. Using this technique, it may be possible to incorporate the biochemical properties of any membrane protein or protein complex in the form of membranes into electronic devices as has been achieved in MinION DNA sequencers. Biological membranes consist of many different molecules, primarily lipids and membrane proteins. In a biological context, the function of membrane proteins often depends on both the protein component and its lipid environment. This manuscript focuses primarily on the protein content of membranes, intentionally neglecting the lipid component of the physiological function of membrane proteins. This aspect is to be addressed in future research.