Multilamellar liposomes entrapping aminosilane-modified maghemite nanoparticles: “magnetonions”

4.6 nm-sized aminosilane-modified maghemite (γ-Fe2O3) nanoparticles (aMNPs) were synthesized and encapsulated into onion-type multilamellar vesicles of soybean phosphatidylcholine (90%mol) and monoolein (10%mol). The magnetic multilamellar vesicles were obtained by shearing lipids with an aqueous dispersion of the preformed aMNPs (ferrofluid). The influence of ferrofluid concentration on the stability of the constitutive lamellar phase and the resulting dispersed onions was analyzed by small-angle X-ray diffraction (SAXD) and cryo-TEM imaging, respectively. When [Fe(III)] <60 mM, stable, magnetic onions were produced with aMNPs inserted inside onion water compartments as isolated or aggregated particles. Encapsulation efficiencies were measured by EPR spectroscopy and magnetic measurements: much higher values (up to 75%) than unilamellar liposomes were found. The deduced aMNP-to-onion ratio increased with ferrofluid concentration before reaching a maximal value of ca. 45 as confirmed by cryo-TEM imaging. When [Fe(III)] >60 mM, uni- or oligolamellar vesicles in addition to onions formed, probably because of a two-phase separation between an aMNP-rich phase and an aMNP-containing lamellar phase as revealed by SAXD.