DNA adsorption to laterally structured charged lipid membranes

A macroscopic surface property, such as a surface's affinity for a certain polymer, may depend significantly on surface parameters on the nanoscopic length scale, such as the size of areas with positive and negative surface charge. In this study, polyelectrolyte adsorption to laterally structured charged surfaces was investigated as a function of the size of the charged surface areas. Polydeoxyribonucleic acid (DNA) was adsorbed onto supported cationic lipid bilayers which were imbedded in a matrix of negative surface potential, and the size of the cationic surface areas was varied from the micrometer down to the subnanometer length scale. The supported lipid bilayers and the adsorbed DNA were imaged with an atomic force microscope, and the DNA adsorption was found to depend on the surface charge density and on the size of the cationic lipid bilayers areas. While on purely cationic lipid bilayers larger than 20 nm a densely packed layer of DNA could be observed, as expected, no DNA could be detected on molecular cocrystals of cationic and anionic lipids where the diameter of the cationic lipid headgroups is only about 0.7 nm. On a 1:1 binary mixture of cationic and neutral lipids, on the other hand, the spacing between adjacent DNA strands was found to double, compared to the purely cationic lipid membranes.