Influence of iron oxide nanoparticles on bending elasticity and bilayer fluidity of phosphotidylcholine liposomal membranes

Iron oxide nanoparticles with improved surface characteristics have tremendous applications in various biomedical fields such as magnetic resonance imaging, hyperthermia, immunoassay and targeted drug delivery. The aim of this work was to study the influence of iron oxide (γ-Fe2O3) nanoparticles on the bilayer fluidity and bending elasticity of zwitterionic phosphatidylcholine liposomal membranes. Small unilamellar vesicles prepared with l-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine lipids were encapsulated with uncoated iron oxide nanoparticles and silica coated iron oxide nanoparticles to study their effect on bilayer fluidity. Anisotropy measurements using the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene and N,N,N-trimethyl-4-(6-phenyl-1,3,5-hexatrien-1-yl) phenylammonium p-toluensufonate did not show a significant difference in the lipid ordering and bilayer fluidity. Thermally induced shape fluctuations of the giant quasi-spherical lipid vesicles were used to study the influence of both types of iron oxide nanoparticles on the bending elasticity modulus kc of the lipid membrane. The results showed that in the case of uncoated iron oxide (in the studies concentration) the obtained value for the bending elasticity modulus does not differ in the frames of the experimental error from that of pure phospholipid membrane. In the case of silica coated iron oxide nanoparticles the bending elasticity modulus of the membrane decreased by 25%.