(464b) Research on the Mechanism of Spontaneous DNA Extension on Grooved Surface Covered with Cationic Lipid Bilayers

We have recently developed a novel DNA optical gene mapping platform. Its working principle relies on the phenomenon that DNA can spontaneously extend along grooves covered with cationic lipid bilayers. Although the physical gene map can be readily obtained from the extended DNA, the mechanism causing DNA extension is not clear. Since DNA extends only along the grooves, it was suggested that there exists an electrostatic energy well for DNA. The origin of the energy well was postulated to be the uneven lipid distribution due to the steric effect that the shape of lipids will affect their distribution on a curved surface. Moreover, we suspect a simple geometry effect may also contribute to the energy well. The geometry effect comes from that fact that DNA on a surface with positive curvature can interact more strongly with lipid molecules. To examine both postulations, we investigated DNA behavior on three sets of bilayers with different composition: (A) DOPC/DOTAP(+), (B) DOPC/EPC(+) and (C) DOPE/EPC(+). The lipids used here have the same tails but different head groups. The experimental results show both the steric and the geometry effect are important. However, the geometry effect is always in favor of DNA extension while the steric effect can either enhance or undermine the phenomenon. We have also investigated the effect of the concentration of the positively charged lipids and found higher concentration always help DNA to extend. In order to quantify the geometry effect, we have derived the electrostatic potential of DNA on curved surface and found the theoretical prediction is in good agreement with the experimental results.