Atomic force microscopy of cationic liposomes

Cationic liposomes, formed from a 1:1 molar mixture of p-ethyldimyristoylph osphatidylcholine (EDMPC) and cholesterol by extrusion through filters, hav e been investigated using atomic force microscopy (AFM). The fluid nature o f liposomes makes them a challenging prospect for imaging by AFM. Tapping-m ode imaging in air and under fluid was carried out with the liposomes depos ited on either mica or mica treated with aminopropylsilane (AP-mica), surfa ces with negative and positive potentials, respectively. The interaction of the liposomes with both surfaces was investigated, and the observed liposo me structure was found to be dependent on the nature of the surfaces. Struc tures close to those expected in solution from light scattering measurement s were observed on the AP-mica surfaces. Tip-induced fusion of individual l iposomes could also be observed. This study illustrates that AFM can be use d as a tool for studying dynamic processes involving lipid vesicles.