Functionalization of colloids with robust inorganic-based lipid coatings

Core-shell colloids, particles covered with polyelectrolyte (PE) multilayer films and lipid bilayer membranes, were prepared through self-assembly processes. The PE multilayer films were fabricated by the layer-by-layer (LbL) assembly of poly(diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) onto colloidal particles. The inorganic-based synthetic lipid, N-[N(3-triethoxysilyl)propylsuccinamoyl]dihexadecylamine (Si-lipid), was employed for membrane formation and was deposited onto the PE-coated particles through electrostatic interaction. The naturally occurring lipid, dimyristoylphosphatidic acid, sodium salt (DMPA), was also used for comparison. Multilayer film buildup on the particles was monitored stepwise by microelectrophoresis, and formation of the lipid bilayers was confirmed by fluorescence microscopy as well as scanning and transmission electron microscopy. The morphological stability of the Si-lipid and DMPA membranes to the surfactant Triton X-100 and ethanol was examined by fluorescence measurements. The Si-lipid bilayer coating was found to be highly stable upon exposure to Triton X-100 and ethanol solutions, even at high concentrations, whereas the DMPA membranes delaminated from the particle surface at low surfactant concentrations and low ethanol content aqueous solutions. The enhanced stability of the Si-lipid film is attributed to the polymerized moiety in the headgroup of the synthetic lipids and H-bonding interactions between adjacent Si-lipid molecules. The Si-lipid systems described here are attractive because of the potential to prepare robust inorganic lipid-based films with controllable properties, for example, thickness, permeability, and stability, both in the form of coatings on particles and as capsular colloids.