Influence of pH and electrolyte on the deposition of cerium oxide nanoparticles on supported lipid bilayers
Journal: Environ. Sci.-Nano, Volume 9, JUN 16, page 1986–1995
Authors: Gu, Wenyu; Liu, Xitong; Yi, Peng
Organizations: Semiconductor Research Corporation, Durham, NC [425-MC-2001, 425.041]
The adhesion of cerium oxide nanoparticles (n-CeO2) to cell membranes is likely a crucial step for initiating the toxic effects of n-CeO2 on biological cells. To investigate the propensity of n-CeO2 to adhere to model cell membranes, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) supported lipid bilayers (SLBs), the deposition attachment efficiencies of n-CeO2 on SLBs were derived using a quartz crystal microbalance. The impact of solution pH and the valence and concentration of the electrolyte on the attachment efficiency was consistent with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The isoelectric points of DOPC membranes and n-CeO2 are pH 4.2 and 7.2, respectively. At pH 8.0, the attachment efficiency between negatively charged SLBs and n-CeO2 increased with increasing NaCl and CaCl2 concentrations. The critical deposition concentrations of NaCl and CaCl2 are 11 and 0.62 mM, respectively. At pH 2.0 and 4.0, both n-CeO2 and SLBs were positively charged. The attachment efficiency increased as the NaCl and CaCl2 concentrations increased due to charge screening by Cl- anions. At pH 5.5, n-CeO2 and SLBs were oppositely charged in NaCl solutions, hence resulting in favorable attachment. In the presence of CaCl2, however, the adsorption of Ca2+ cations reversed the charge of SLBs to become positive and thus led to unfavorable deposition. Negligible detachment of n-CeO2 from SLBs was observed upon exposure to low ionic strength solutions or pH changes, indicating irreversible attachment.
