MANIPULATION AND MOLECULAR RESOLUTION OF A PHOSPHATIDYLCHOLINE-SUPPORTED PLANAR BILAYER BY ATOMIC-FORCE MICROSCOPY

The morphology of supported planar bilayers has been investigated belo w phase transition temperature by atomic force microscopy in contact a nd tapping mode. The bilayers were formed by the vesicle-spreading tec hnique. In contact mode at low scanning forces of about 1 nN true mole cular resolution could be achieved for supported phosphatidylcholine b ilayers. The resolution was confirmed by experiments that captured the location, average area of individual lipid headgroups and the manipul ation of the bilayer surface. Repeated scanning in contact mode shifte d the random topology of the surface consecutively to a striped patter n. Height profiles of defect-containing bilayers were analyzed. The sh ape of the defects became smooth by repeated scanning. The height prof iles allowed the estimation of the indentation of the tip into the sur face-adsorbed membrane. In tapping mode a disordered pattern of headgr oups became visible. Our morphological data at molecular resolution su ggest that the native arrangement of the choline head-groups is disord ered, free of large packing defects and becomes ordered in Schallamach waves by scanning in contact mode.