Self Assembly of Air-Stable Cationic Lipid Bilayers on Mica and Silicon

Lipid bilayers are one of the most fundamental part of a human cell. These bilayers control the passage in and out of ions and molecules such as proteins or drugs. One method to study these lipid bilayers is by making supported lipid bilayers on a solid substrate. These supported lipid bilayers can be readily modified for the research of interest, and their substrates can be materials like quartz or gold that can be used as part of the optical or electrical characterization method used to study the bilayer structure properties. The majority of studies on supported lipid bilayers is done with the lipid bilayer immersed in an aqueous phase. Characterization is commonly done using fluorescence mircroscopy in a flow cell, or liquid cell AFM. Although air stable bilayers would be useful in biosensors and other bioelectronic devices, there are only a few supported lipid bilayers in the literature that are air stable enough to permit structural characterization, and they often show heights that are not really consistent with bilayer structure.

This dissertation describes the self-assembly of air-stable cationic lipid bilayers that are stable to rinsing and for at least a month of storage in air. The original goal of the project was to make patterned octadecyltrichlorosilane (OTS) that could act as a support to anchor a cationic lipid monolayer; the function of this anchored monolayer would be to attract anionic DNA origami to the monolayer and allow them to bind but still retain mobility on the fluid lipid surface. Our group had previously developed a 'molecular lift-off' process to make patterned cationic siloxane monolayers, but these depositions are done in water, which is incompatible with OTS. In order to modify the molecular lift-off process to make patterned OTS, I used hexane, which does not dissolve or swell the PMMA resist, to deposit films of OTS on silicon oxide. This deposition process gave monolayers of comparible quality to those made by a tedious dry-box deposition using solvents that swelled or dissolved the PMMA. I then tested several cationic lipids to see which would be able to form films on OTS, and picked 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine (Ethyl PC) to carry out the rest of the study. I looked at the interaction of this lipid with mica, silicon, and silicon/OTS using traditional liquid cell AFM, air AFM, and contact angle measurements. Although the original patterning goal did not prove feasible, Ethyl PC did form air stable bilayers on mica and silicon. The bilayers showed very high coverage (>90%) but numerous attempts to anneal the multiple small domains and to bind DNA origami to them failed.

In the final chapter the need for scientific outreach in the K-6 community is addressed. I spent 2 years helping teachers become more confident with advanced scientific topics. This confidence was transferred into the classroom where students in grades K-6 were exposed to the theory and concepts of scanning electron microscopy.

Students in Grade 6 were given hands-on training on the use of a portable scanning electron microscope (SEM) and then independently used the microscope in their middle school classroom.