Dynamic surface pressure measurements, coupled with optical and electron microscopy, are used to examine interactions between lipid membranes and engineered nanoparticles as a function of nanoparticle concentration and surface charge, and membrane composition and interfacial tension. This approach is reminiscent of that for peptides or proteins, where their interactions with lipid monolayers have been described based on a maximum �insertion� pressure (MIP). The objective is to develop an approach that can detect the kinetics of nanoparticle binding and membrane reorganization, and to test the MIP concept for engineered nanoparticles. Saturated dipalmitoylphosphatidylcholine (DPPC, zwitterionic) and dipalmitoylphosphatidylglycerol (DPPG, anionic), and unsaturated dioleoylphosphatidylcholine (DOPC, zwitterionic) and dioleoylphosphatidylglycerol (DOPG, anionic) are used to form single or mixed monolayers at air/water interfaces with varying biophysical structure and phase behavior. Anionic glycerol lipids are used to create model bacterial membranes, and silver nanoparticles with charged or neutral organic surface coatings are used because of their biological relevance (e.g. antibacterial properties). Our initial results have shown that interactions are primarily dependent upon the degree of electrostatic and hydrophobic interactions, and the intermolecular spacing between the lipids. At low initial surface pressures (~10 to 15 mN/m), cationic nanoparticle binding leads to a large increase in surface pressure that takes place over many hours. In contrast, at high initial surface pressures (> 15 mN/m), there is a small increase in surface pressure over a much shorter length scale. These differences reflect changes lipid packing and mobility, and the lipid-condensing effect the nanoparticles have at the air/water interface. Additional studies are underway to determine the effects of salts and to determine how proteins competitively bind to modulate interactions.

Nanoparticle �insertion� into anionic and phase separated lipid monolayers

248th National Meeting (2014)

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