Supported bilayer lipid membrane arrays on photopatterned self-assembled monolayers

This work demonstrates the use of photocleavable cholesterol derivatives to create supported bilayer lipid membrane arrays on silica. The photocleavable cholesteryl tether is attached to the surface by using the reaction of an amine-functionalized self-assembled monolayer (SAM) and the N- hydroxysuccinimide-based reagent 9. The resultant SAM contains an orthonitrobenzyl residue that can be cleaved by photolysis by using soft (365 nm) UV light regenerating the original amine surface, and which can be patterned using a mask. The photoreaction yield was ≈75% which was significantly higher than previously found for related ortho-nitrobenzyl photochemistry on gold substrates. The SAMs were characterized by means of contact angle measurements, ellipsometry and X-ray photoelectron spectroscopy. Patterned surfaces were characterized with SEM and AFM. After immersing the patterned surface into a solution containing small unilamellar vesicles of egg phosphatidylcholine (PC), supported lipid membranes were formed comprised of lipid bilayer over the amine functionalized "hydrophilic" regions and lipid monolayer over the cholesteryl "hydrophobic" regions. This was confirmed by fluorescence microscopy and AFM. FRAP studies yielded a lateral diffusion coefficient for the probe molecule of 0.14±0.05 μm ²s^-1 in the bilayer regions and ≈0.01 μm ²s^-1 in the monolayer regions. This order of magnitude difference in diffusion coefficients effectively serves to isolate the bilayer regions from one another, thus creating a bilayer array.