We present images of the polar or headgroup regions of bilayers of dimyristoyl-phosphatidylethanolamine (DMPE), deposited by Langmuir-Blodgett deposition onto mica substrates at high surface pressures and imaged under water at room temperature with the optical lever atomic force microscope. The lattice structure of DMPE is visualized with sufficient resolution that the location of individual headgroups can be determined. The forces are sufficiently small that the same area can be repeatedly imaged with a minimum of damage. The DMPE molecules in the bilayer appear to have relatively good long-range orientational order, but rather short-range and poor positional order. These results are in good agreement with x-ray measurements of unsupported lipid monolayers on the water surface, and with electron diffraction of adsorbed monolayers.
Bibliographical noteFunding Information:
Financial support was provided by a Whitaker Foundation Grant (Dr. Longo, Dr. Zasadzinski), an IBM Manufacturing Fellowship (Dr. Weisenhorn), the National Science Foundation under grants CBT86-57444 (Dr. Zasadzinski, Dr. Helm), and DMR89-17164 (Dr. Gould, Dr. Hansma) and the Office of Naval Research under grant N00014-90-J-1551 (Dr. Zasadzinski).