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The Effect of pH on the DNA Adsorption by the Lipid Monolayer at the
Air-liquid Interface as Investigated by X-ray and Neutron Reflectivity
J.-C. Wu (吳瑞慶)1, T.-L. Lin (林滄浪)1, U.-S. Jeng (鄭有舜)2, H.-Y. Lee (李信義)2,
M.-C. Shih (施明智)3, and N. Torikai (鳥飼直也)4
1
Department of Engineering and System Science, Tsing Hua University, Hsinchu, Taiwan
2
National Synchrotron Radiation Research Center, Hsinchu, Taiwan
3
Department of Physics, Chung Hsin University, Taichung, Taiwan
4
Neutron Science Laboratory (KENS), Institute for Materials Structure Science, High Energy
Accelerator Research Organization (KEK), Tsukuba, Japan
We have studied the DNA adsorption by the mixed DPPC/DC-Chol monolayer at the air-liquid
interface. The mixed monolayers with and without the DNA adsorption were prepared by the
classic Langmuir-Blodgett (LB) technique by transferring the monolayer onto silicon wafers.
Recently, the studies on the DNA related nanotechnologies have attracted much interest because of
its relevance to applications in biosensors, gene delivery, and specific molecular recognition. A
synthetic charged lipid, DC-Chol (3b-[N-(Dimethylaminoethane)-carbamoyl]-cholesterol),
molecular weight 537.3, was used to mix with the DPPC to form the monolayer at the air-liquid
interface. The DNA solution was at a concentration of 1 micro molar. X-ray reflectivity
measurements were carried out with LB films prepared on silicon wafers for mixed DPPC/DC-Chol
monolayer at different mixing ratios. In-situ neutron reflectivity measurements were done at the
ARISA, KENS, KEK. It was found that by changing the pH from 7 to 2, the DNA adsorption by
the lipid monolayer was greatly enhanced. Thick DNA layer was found to form underneath the
lipid monolayer. Detail analysis will be presented.