Cationic Magnetoliposomes

Abstract

Magnetoliposomes (MLs) consist of nanosized, magnetisable iron oxide cores (magnetite, Fe₃O₄) which are individually enveloped by a bilayer of phospholipid molecules. To generate these structures, the so-called water-compatible magnetic fluid is first synthesized by co-precipitation of Fe²⁺ and Fe³⁺ salts with ammonia and the resulting cores are subsequently stabilized with lauric acid molecules. Incubation and dialysis of this suspension with an excess of sonicated, small unilamellar vesicles, ultimately, results in phospholipid-Fe₃O₄ complexes which can be readily captured from the solution by high-gradient magnetophoresis (HGM), reaching very high yields. Examination of the architecture of the phospholipid coat reveals the presence of a typical bilayered phospholipid arrangement. Cationic MLs are then produced by confronting MLs built up of zwitterionic phospholipids with vesicles containing the relevant cationic lipid, followed by fractionation of the mixture in a second HGM separation cycle. Data, published earlier by our group (Soenen et al., ChemBioChem 8:2067-2077, 2007) prove that these constructs are unequivocal biocompatible imaging agents resulting in a highly efficiënt labeling of biological cells.