Investigations of shape change and pore formation of giant vesicles induced by magnetite nanoparticles

Abstract

The deformation and poration of lipid membranes of giant unilamellar vesicles (GUVs) induced by magnetite nanoparticles (MNPs) have been investigated. The membranes were prepared by using natural swelling method where a mixture of negatively charged dioleoylphosphatidyglycerol (DOPG) and neutral diolyphosphatidycholine (DOPC) or only DOPC/DOPG are used. The value of zeta potential of synthesized MNPs is -21.3 mV which confirmed that the synthesized MNPs is anionic. The degree of deformation is measured by compactness (C) and pore formation is investigated by leakage of sucrose. The value of C is increased with the increase of time and also NPs concentration. The average value of C at 30 min for negatively charged and neutral membranes are 1.08 ± 0.002 and 1.35 ± 0.017, respectively. The fraction of deformation is increased with the increase of time and it is 0, 0.15 ± 0.02, 0.27 ± 0.02, 0.36 ± 0.01, 0.42 ± 0.04 and 0.51 ± 0.02 for 0, 10, 20, 30, 40 and 50 min, respectively. The fraction of deformation is increased with increased surface charge density in the membranes, at 50 min the fraction of deformation is obtained 0.36 ± 0.02, 0.51 ± 0.02 and 0.62 ± 0.02 for 20, 40 and 60% DOPG, respectively at 150 mM salt in buffer. The fraction of deformation is increased with decreased of salt concentration in buffer which is obtained 0.82 ± 0.02, 0.62 ± 0.02 and 0.56 ± 0.02 for 50, 150 and 300 mM salt concentration in buffer at 50 min, respectively. The time of stochastic pore formation is slower for charged membrane than neutral one. A negligible effect of MNPs is observed in DOPG membrane. These results indicate that the deformation and poration in the charged and neutral membranes are driven by the nonspecific electrostatic attraction and MNPs have a higher adsorption affinity in neutral membrane than charged one. The adsorption of NPs imposes the mismatch of surface area between the inner and the outer monolayer of bilayer, inducing the deformation of GUVs. Adhesion of MNPs induce lateral surface tension in the membrane, leading to transmembrane poration in GUVs.