(590e) Integration of Large Nanoparticles within Vesicle Bilayers Via Adaptive Surface Chemistry

The incorporation of inorganic nanoparticles into lipid bilayers has important implications for medical imaging and nanoparticle actuated vesicles for controlled drug release.  Depending on the material, the nanoparticle core imparts additional functionalities such as enhanced fluorescence^, plasmonic excitation, or magnetic actuation.  The magnitude of these effects scale strongly with particle diameter D. Consequently, it is often desirable to use larger particles with dimensions exceeding the thickness of lipid bilayers (typically, ~4 nm).  Existing methods for incorporating NPs into bilayer structures are limited to small particles (less than ~6 nm) functionalized with hydrophobic surfaces that “fit” within the hydrophobic core of the membrane.  Larger particlesdo not fuse with lipid bilayers but rather form lipid covered NP micelles as described by thermodynamic models.  Regardless of their size, hydrophobic particles are also difficult to incorporate into preformed aqueous vesicles (or living cells) without the use of stabilizing detergents that must subsequently be removed.  By contrast, NPs functionalized with mixed monolayers containing both hydrophobic and hydrophilic (cationic) ligands have been shown to penetrate the cell membrane and still dissolve easily in water.  Such particles have the interesting ability to adapt their surface chemistry in response to environmental cues as further evidenced by the formation of amphiphilic, Janus-type NPs at liquid interfaces.  Recent theoretical results suggest that environmentally-responsive particles containing binary mixtures of mobile ligands – one hydrophobic, one hydrophilic – can penetrate and fuse with lipid bilayers even when the particle dimensions (~10 nm) greatly exceed that of the membrane.  Here, we confirm this prediction experimentally and demonstrate that large (up to 10 nm) gold nanoparticles functionalized with amphiphilic mixed monolayers incorporate spontaneously into the walls of surfactant vesicles.