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Engineered oxide nanoparticles (NPs) are widely applied in insulators,catalyzers,paints,cosmetic products,textiles and semiconductors.Their attachment on cell membrane may lead to cytotoxicity.The effects of Al2O3,Fe2O3,SiO2,TiO2 and ZnO NPs on membrane integrity and fluidity were studied using giant or small unilamellar vesicles in this study.Al2O3 and SiO2 NPs disrupted the oppositely charged membrane,indicating the important role of electrostatic attraction.However,Fe2O3,TiO2 and ZnO NPs did not cause serious membrane disruption as Al2O3 and SiO2 NPs.Membrane fluidity was evaluated by the generalized polarity (GP) values of Laurdan fluorescent emission.SiO2 NPs induce the membrane gelation of both positively and negatively charged membrane.Al2O3 and ZnO NPs induced the gelation of the oppositely charged membrane,but did not cause obvious membrane gelation to the like charged membrane.The phosphollpid molecular structural changes after NP exposure were analyzed by Fourier transform infrared (FT-IR) spectroscopy.FT-IR spectra revealed the hydrogen bond formation between NPs and the carbonyl/phosphate groups of phospholipids.Al2O3 and SiO2 NPs showed strongest evidence of hydrogen bonding on their FT-IR spectra.It was consistent with the microscopic observation and fluorescent data that Al2O3 and SiO2 NPs caused more serious membrane disruption and gelation.This study on membrane damage provides further knowledge on the cytotoxicity of nanomaterials and the safety of NP application.