Atomic Force Microscopy of Cationic Liposomes

Abstract

Cationic liposomes, formed from a 1:1 molar mixture of p-ethyldimyristoylphosphatidylcholine (EDMPC) and cholesterol by extrusion through filters, have been investigated using atomic force microscopy (AFM). The fluid nature of liposomes makes them a challenging prospect for imaging by AFM. Tapping-mode imaging in air and under fluid was carried out with the liposomes deposited on either mica or mica treated with aminopropylsilane (AP-mica), surfaces with negative and positive potentials, respectively. The interaction of the liposomes with both surfaces was investigated, and the observed liposome structure was found to be dependent on the nature of the surfaces. Structures close to those expected in solution from light scattering measurements were observed on the AP-mica surfaces. Tip-induced fusion of individual liposomes could also be observed. This study illustrates that AFM can be used as a tool for studying dynamic processes involving lipid vesicles.