Characterization of lipid membrane interactions with solid surfaces
Ganna Reint, Chemistry
Sensors and other analytical devices incorporating molecular lipid films are highly versatile, due to the many possibilities for incorporation and conjugation of sensing components. Controlled and efficient area coverage of the sensor surface by a lipid film is particularly important, and dependent on lipid compositions, interface structure and the conditions in the local liquid environment. To investigate the conditions in detail, we employ a microfluidic pipette in a «lab on a membrane» to form planar lipid films of different compositions on a variety of solid engineering substrates, and observe the process of membrane formation with a laser scanning confocal microscope. The formation of films occurs as a result of adhesion and rupturing of small unilamellar vesicles (SUVs) in the circulation zone of the pipette upon contact with the surface, leading to an homogenous fluid lipid membrane patch. Mono- or bilayer films are formed, depending on the substrate material.
We perform Fluorescence Recovery after Photobleaching (FRAP) to determine the fluidity of the films on the solid supports, and calculate the diffusion constants. The investigation comprises hard and soft materials substrates typically used in biointerface development: Au, borosilicate glass, SiO2, quartz, Si3N4, SiC, SU-8, graphene and Teflon-AF. The results show an enhanced formation of membranes on nearly all surfaces from precursor vesicles containing the transfection lipid DOTAP. The diffusion constants of the lipids in the deposited films display variations, which we attribute to differences in friction between the fluid molecular films and the surfaces, arising from both electrostatic and hydrophilic/phobic interactions.