Neutron and X-ray reflectivity studies on DNA adsorption on mixed DPPC/DC-Cholesterol monolayers

We have studied DNA adsorption on mixed DPPC/DC-Chol monolayers. Solid supported mixed monolayers on silicon wafers were prepared using Langmuir–Blodgett (LB) dipping technique. Neutron and X-ray reflectivity measurements were used to characterize these LB monofilms. For LB monofilms with DNA adsorption, the reflectivity data of the DPPC/DNA film are very close to that from the DPPC film, which indicates only minor DNA adsorption on the pure DPPC monolayer. Increasing the percentage of DC-Chol, film thickness increases. The DC-Chol/DNA film is thicker than the pure DC-Chol film (film thickness 18 Å) by about 9 Å due to the presence of adsorbed DNA. A model is presented to explain the structure of the lipid/DNA film.