470169 Peg-Coated Silver Nanoparticle Surface Activity and Lipid Monolayer Interactions
This study investigates the interactions between polyethylene glycol (PEG)-coated silver NPs and lipid monolayers using dynamic surface-pressure measurements and hyperspectral microscopy. PEG-coated nanoparticles are generally considered to be inert, however, there have been a number of studies showing that PEG and PEG-coated NPs are surface active, which would promote their insertion into lipid monolayers or membranes. Langmuir monolayer techniques were employed to measure the surface pressure-area (π–A) isotherms of the lipid monolayer as a function of NP concentration. Monolayers were formed by depositing solutions of dioleoylphosphocholine/dioleoylphosphoglycerol (DOPC/DOPG; 1:1 mole ratio) at the air-water interface to mimic an anionic membrane. A suspension of PEG-coated silver NPs was injected below the lipid monolayer in the water subphase and the interaction with the monolayer was examined as a function of time.
Isotherms were conducted in the absence of the lipid monolayer to determine the NPs surface activity and to distinguish between the surface activity of the excess coating polymer coating from coated NPs themselves. Our results show that the PEG-coated NPs are surface-active and compete with the lipids for adsorption at the air/water interface. Hyperspectral microscopy and TEM imaging of the nanoparticles and lipid monolayer at the interface confirm these observations. In the absence of lipids, the NPs increase the surface pressure up to 45 mN/m upon compression before the NPs surface layer collapsed. In the presence of lipids, the NPs and lipids act cooperatively to increase the π. At high NPs concentrations, corresponding to the NPs completely covering the interface, the π–A isotherms more closely resembled that for NPs than for lipids. NP surface activity is predominantly (~80%) due to the excess coating material rather than the NPs themselves. Low NP concentrations lead to an increase in π due to increase lipid packing and the inherent surface activity of the NPs, and high NP concentrations lead to monolayer collapse due to lipid desorption from the interface.