(537g) Interfacial Binding of Anionic Liposome and Anionic SPIO Nanoparticles

Interactions between biological membranes and inorganic nanoparticles play an important role in nanomedicine and nanotoxicology. Adhering nanoparticles can affect lipid phase behavior and transmembrane permeability, and, when strongly adhering, can lead to pore formation and nanoparticle invagination. This work examines the effects of temperature and electrolyte concentration on the interaction between partially anionic lipid bilayer vesicles and anionic superparamagnetic iron oxide nanoparticles. Although the liposomes and nanoparticles are like-charged, they exhibit different charge densities. Extruded liposome (~200 nm hydrodynamic diameter) were prepared in water using dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) at a molar ratio of 3:1. The nanoparticles had a core diameter of 5 nm and were coated with a carboxylated polymer to yield an average hydrodynamic diameter of 16 nm. Despite being like-charged, preliminary dynamic light scattering data at 25^oC shows nanoparticle binding to gel-phase liposomes and causes liposome aggregation. Isothermal titration calorimetry results suggest that this process was driven by entropic (hydrophobic) interactions. Increasing temperature to 45^oC or adding salt (NaCl or phosphate buffered saline, PBS) reversed liposome aggregation. Current work is focused on elucidating the effects of temperature and electrolyte concentration on nanoparticle binding, liposome aggregation, and liposome fusion.