Crystalline phase and surface coating of AlO nanoparticles and their influence on the integrity and fluidity of model cell membranes.

Aluminium oxide nanoparticles (AlO NPs) potentially cause health hazards after their release into the environment. The crystalline phase of AlO NPs determines their surface structure and the number of functional groups. The adsorption of natural organic matter (NOM) or biomolecules on the surface AlO NPs also alters their surface properties and subsequent interactions with organisms. In this study, the roles of the AlO crystalline phase and the surface coating of the nanoparticles on the membrane integrity and fluidity were investigated. Giant and small unilamellar vesicles (GUVs and SUVs) were prepared as model cell membranes to detect membrane disruption after exposure to AlO NPs. Due to amorphous structure and high surface activity of γ-AlO NPs, they had a stronger affinity with the membrane and caused more serious membrane rupture than that of α-AlO NPs. The deposition of AlO NPs on the membrane and the induced membrane disruption were monitored by a quartz crystal microbalance with dissipation (QCM-D) method. HA-coated AlO NPs disrupted the SUV layer on the QCM-D sensor, while BSA-coated AlO NPs only adhered to the membrane and induced unremarkable vesicle disruption. In addition, untreated γ-AlO NPs induced remarkable gelation of a negatively charged membrane, but other types of AlO NPs caused negligible membrane phase changes. The outcomes of this study demonstrate that the crystalline phase of the AlO NPs affects the integrity and fluidity of cell membranes. The protein coatings on the NPs weaken the NP-membrane interaction, while HA coatings increase the damage of the NP-induced interaction.