A Cholesterol‐Based Tether for Creating Photopatterned Lipid Membrane Arrays on both a Silica and Gold Surface

Abstract

Surfing gold and silica! A new cholesterol-based tether was attached to both amine-functionalised silica and gold surfaces. The resultant self-assembled monolayers, which can be deep-UV-patterned, were used in attaching essentially equivalent patterned supported lipid bilayers both on silica for fluorescence studies (left figure) and on gold for impedance studies (right figure).We report a new cholesterol-based self-assembled monolayer (SAM) for use in attaching lipid membranes to both gold and silica surfaces that can be patterned by deep UV (254 nm) photolysis. It allows essentially equivalent patterned supported bilayers to be created both on gold for impedance studies and on silica for fluorescence studies. On either surface an amine-functionalised SAM is reacted with an N-hydroxysuccinimidylcarbonyl-functionalised EO3-cholesteryl derivative. The formation of the amine-functionalised SAM and its reaction with the EO3-cholesteryl derivative were followed by contact-angle measurements, ellipsometry and X-ray photoelectron spectroscopy. The resultant layer of cholesterol tethers was patterned by deep UV photolysis, which regenerates the original SiO(2) surface in exposed regions on a silica substrate and oxidises thiol groups on a gold substrate. This patterned surface containing hydrophilic SiO(2) (or -OH groups) and hydrophobic cholesterol tether regions can be converted to a surface patterned with supported lipid bi- and monolayers (respectively) by immersing in a solution of small unilamellar vesicles of egg yolk phosphatidycholine. The formation of the lipid bi- and monolayer regions on the silica surface was evidenced by fluorescence microscopy. Crucially the bilayer regions remain fully fluid yielding lipid mobilities comparable to those found in physisorbed bilayers. Furthermore charged fluorescent lipids are shown to migrate in an applied field thus providing a platform for the studying the electrophoresis (potentially) for a wide range of charged membrane components, such as membrane proteins. The formation of the patterned lipid membrane on the gold surface was confirmed by electrochemical impedance measurements.