Polymer-supported lipid bilayers on benzophenone-modified substrates

Solid-supported lipid membranes are important for their roles in fundamenta l biophysical research as well as in applications such as biosensors; In ou r study, lipopolymers containing alkyl side chains were synthesized and a m ixture of the lipopolymer and free lipids was preorganized at the air-water interface and then transferred to a solid substrate using the Langmuir-Blo dgett technique. A photochemical reaction between a substrate-functionalize d benzophenone and C-H bonds on the lipopolymer was used to attach the lipo polymers to the substrate. The final assembly of the membrane was completed by vesicle fusion. Langmuir film experiments at the air-water interface in dicate tighter molecular packing for the lipopolymers with 28 mol % alkyl s ide chains than for the ones with 22 mol %. Atomic force microscopy images point to phase separation of lipopolymers on the substrates due to their de wetting from hydrophobic surfaces. However, a mixture of lipopolymers and f ree lipids formed a smooth film on the same substrate. After the addition o f the second lipid layer on the lipopolymer/free lipid layer, the fluoresce nce images of the polymer-supported bilayer suggested that the distal lipid layer is homogeneous on the micrometer scale. The relaxation of the fluore scent probe lipids was analyzed after application of an electric field to d etermine their diffusion coefficient; the distal lipid layer was mobile wit h an average diffusion coefficient of similar to0.1 mum(2)/s. Moreover, the immobile fraction of the lipids in the distal layer was estimated to be ar ound 15%.