Effects of Pore Size and Tethering on the Diffusivity of Lipids Confined in Mesoporous Silica

Incorporation of lipid assemblies on the surface and within pores of mesoporous silica particles provides for biomimetic approaches to analyte sensing and separations using high surface area platforms. This work investigates the effect of pore confinement on the location and the diffusivity of lipid assemblies in mesoporous silica spherical particles (SBAS) as a function of nanopore diameters (nonporous, 3.0, 5.4, and 9.1 nm), which span the range of the thickness of the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine lipid bilayer (≈4 nm). Large-diameter SBAS are imaged with sufficient spatial resolution to distinguish lipids at the exterior surface and in the center of the particles. Lipids incorporated on the silica by evaporation deposition exist as exterior lipid bilayers on all particles and lipid assemblies in the pores of 5.4 and 9.1 nm pore diameter materials. Lipid diffusivity increases with pore size and decreases in the presence of bilayer tethering functional groups. Lipid diffusivity in the core of the particles is similar to the surface diffusivity, consistent with long-range mobility in accessible, ordered (but randomly oriented) mesopores of SBAS materials. This work presents a framework for interpreting high density loading of lipid bilayers and their function within mesoporous materials.