Stability of free-standing tetraether planar membranes in microchips

Here, we used electrochemical impedance spectroscopy to demonstrate that the polar lipid fraction E (PLFE), a major bipolar tetraether lipid component isolated from thermoacidophilic archaea, can form free-standing planar membranes with remarkable membrane stability in comparison to planar membranes made of diester lipids or triblock copolymers. Stable PLFE planar membranes were generated on micro-pores ranging from 20 to 200 mu m in polydimethylsiloxane (PDMS) thin films embedded in a specially made glass/silicon two-chamber microchip. The micro-pore-containing PDMS thin film was fabricated by using a double-side molding approach, which created surface flatness on both sides of the film, removing pore cliffs and thus reducing the variations in the fabrication of free-standing planar membranes. We found that, at 11-39 degrees C, PLFE free standing planar membranes embedded in the microchips not only did not break, but also exhibited electrical impedance virtually invariant over the entire time period (5-50 h) examined. The stability of PLFE free-standing planar membranes, which is on the order of days and achieved without having lipid polymerization nor using nano-pores, is unusual for naturally occurring lipids. This extraordinary stability is attributed mainly to the strong PLFE-PLFE hydrogen bonding and van der Waals interactions and to the possible interactions between PLFE molecules and the PDMS substrate. This study indicates that the use of PLFE can greatly reduce the instability problem of traditional black lipid membranes and that incorporating unusually stable PLFE planar membranes into microdevices is feasible. In summary, bipolar tetraether lipids such as PLFE are excellent materials to make extremely stable yet biologically relevant free-standing planar membranes suitable for use in chip-based membrane technologies.