(353c) Dynamic Nanoparticle Restructuring of Lipid Monolayers: Coating Amphiphilicity Trumps Charge

Langmuir monolayers formed by phospholipids deposited at air/water interfaces represent simple, but effective model biological membranes for studying interaction mechanisms between engineered nanoparticles and lipid membranes. This work describes the use of dynamic surface pressure measurements, coupled with optical and electron microscopy, to elucidate these mechanisms as a function of nanoparticle concentration and surface charge, and membrane composition, tension, and two-dimensional phase state. 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 with varying biophysical structure and phase behavior. Silver nanoparticles were examined with anionic, cationic, or PEGylated surface coatings because of their biological and commercial relevance. By varying the interlipid spacing, or lipid area per molecule, nanoparticle binding dynamics and the minimum insertion pressure were determined analogous to that for peptides or proteins. Unexpectedly, the PEGylated nanoparticles exhibited the greatest interaction with the lipid monolayers. Hydrophobic interactions, which were dominant for PEGylated nanoparticles and also present for charged nanoparticles, were responsible for monolayer insertion independent of monolayer charge. In contrast, electrostatic and charge-dipole interactions with PCs were primarily responsible for lipid condensation.