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 l ength scale, such as the size of areas with positive and negative surface c harge. In this study, polyelectrolyte adsorption to laterally structured ch arged surfaces was investigated as a function of the size of the charged su rface areas. Polydeoxyribonucleic acid (DNA) was adsorbed onto supported ca tionic lipid bilayers which were imbedded in a matrix of negative surface p otential, and the size of the cationic surface areas was varied from the mi crometer down to the subnanometer length scale. The supported lipid bilayer s 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 th e 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 do uble, compared to the purely cationic lipid membranes.