Combined study of X-ray reflectivity and atomic force microscopy on a surface-grafted phospholipid monolayer on a solid.

We investigated the detailed structure of a surface-grafted phospholipid monolayer, which was polymerized in situ onto a methacryloyl-silanized solid surface. By the combined study of X-ray reflectivity and atomic force microscopy, the in situ polymerization step of the lipid molecules are sufficiently detailed to reveal the molecular structure of lipid molecules before and after in situ polymerization. From the data of the X-ray reflectivity, we confirmed that the in situ polymerization process produces a flat lipid monolayer structure and that the lipid monolayer is substantially grafted on a silanized surface by chemical bonding. After the polymerization and washing processes, the thickness of the head group was 9 angstroms and the thickness of the tail group was 21 angstroms. The surface morphology of the polymerized phospholipid monolayer obtained by the measurements of atomic force microscopy was consistent with the results of the X-ray reflectivity. The cross-sectional analysis shows that the surface coverage of lipid molecules, which are chemically grafted onto a silanized surface, is approximately 89%.