Effect of oxide nanoparticles on the morphology and fluidity of phospholipid membranes and the role of hydrogen bonds.

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 AlO, FeO, SiO, TiO and ZnO NPs on membrane integrity and fluidity were studied using giant or small unilamellar vesicles in this study. AlO and SiO NPs disrupted the oppositely charged membrane, indicating the important role of electrostatic attraction. However, FeO, TiO and ZnO NPs did not cause serious membrane disruption as AlO and SiO NPs. Membrane fluidity was evaluated by the generalized polarity (GP) values of Laurdan fluorescent emission. SiO NPs induce the membrane gelation of both positively and negatively charged membrane. AlO and ZnO NPs induced the gelation of the oppositely charged membrane, but did not cause obvious membrane gelation to the like charged membrane. The phospholipid 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. AlO and SiO NPs showed strongest evidence of hydrogen bonding on their FT-IR spectra. It was consistent with the microscopic observation and fluorescent data that AlO and SiO 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.