Adsorbed and free lipid bilayers at the solid-liquid interface viewed by specular and off-specular reflectivity

The current biological model membrane constituted of a single bilayer deposited on a substrate has been improved by adding a second bilayer. This one, called “free bilayer”, floats 20-30 A above the first. Carefully optimised X-ray reflectivity measurements have allowed a precise characterisation of the structure out of the plane of the membrane and a good description of the in-plane fluctuations. This work has opened new possibilities for investigating interaction between membrane lipids and soluble proteins, especially for peptides too small to be visible with other techniques.