Hydrophobic silver nanoparticles interacting with phospholipids and stratum corneum mimic membranes in Langmuir monolayers.

The interaction of hydrophobic silver nanoparticles with different phospholipids and stratum corneum mimic (SCM) membranes is studied in Langmuir monolayers. Thus, silver nanoparticles coated with oleic acid (AgNP-OA) were synthesized, characterized and incorporated in Langmuir monolayers of single phospholipids -having different chain length, saturation degree and phase state- or of a SCM mixture. The incorporation of AgNP-OA to the lipid monolayers generated an expansion of the monolayers and a decrease of the surface compressional modulus compared to the pure lipid. X-ray photoelectron spectroscopy (XPS) suggested that the zwitterionic choline-phospholipids can be adsorbed onto the nanoparticles' surface, which is relevant considering that phospholipids are the major constituents of the cell membrane. We also studied the changes in the topography at the mesoscale level using Brewster angle microscopy. We found the most prominent changes in the lipids with liquid-condensed phase, such as SCM, showing segregation of their components. This could have major implications in the barrier function of the membrane, affecting for example the skin permeability towards hydrophobic nanoparticles. Finally, the capability of hydrophobic AgNP-OA for delivering Ag+ ions was studied in aqueous media in the absence and presence of phospholipids. In both conditions, AgNP-OA released Ag+ at reported-bactericidal concentrations, being double in the presence of phospholipids.