Characterization of single biological membranes at the solid–liquid interface by X-ray reflectivity

We demonstrate that 18 keV X-rays can be used to perform reflectometry on single, phospholipid bio-membranes at the solid–liquid interface. Two different membrane systems were investigated; a single component, fluid phase membrane of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and a two component, predominantly gel phase membrane composed of 1:9 1,2-dilauryl-sn-glycero-3-phosphocholine (DLPC):1,2-distearyl-sn-glycero-3-phosphocholine (DSPC). The increased dynamic range of X-ray reflectivity over comparable neutron reflectivity measurements enabled the density distribution of the membranes to be determined with much greater precision. The increased resolution allowed subtle features in membrane structure and leaflet segregation to be revealed. Previously, characterization of biomimetic structures normal to a “buried” interface was the domain of neutron reflectivity.