Influence of Sensor Coating and Topography on Protein and Nanoparticle Interaction with Supported Lipid Bilayers

Abstract

Supported lipid bilayers (SLBs) have proven to be valuable model systems for studying the interactions of proteins, peptides, and nanoparticles with biological membranes. The physicochemical properties (e.g., topography, coating) of the solid substrate may affect the formation and properties of supported phospholipid bilayers, and thus, subsequent interactions with biomolecules or nanoparticles. Here, we examine the influence of support coating (SiO 2 vs Si 3 N 4 ) and topography [sensors with embedded vs protruding gold nanodisks for nanoplasmonic sensing (NPS)] on the formation and subsequent interactions of supported phospholipid bilayers with the model protein cytochrome c and with cationic polymer-wrapped quantum dots using quartz crystal microbalance with dissipation monitoring and NPS techniques. The specific protein and nanoparticle were chosen because they differ in the degree to which they penetrate the bilayer. We find that bilayer formation and subsequent non-penetrative association with cytochrome c were not significantly influenced by substrate composition or topography. In contrast, the interactions of nanoparticles with SLBs depended on the substrate composition. The substrate-dependence of nanoparticle adsorption is attributed to the more negative zeta-potential of the bilayers supported by the silica vs the silicon nitride substrate and to the penetration of the cationic polymer wrapping the nanoparticles into the bilayer. Our results indicate that the degree to which nanoscale analytes interact with SLBs may be influenced by the underlying substrate material.

Streptavidin Coverage on Biotinylated Surfaces

“…The nanodiscs have a thickness of ∼20 nm; the silicon nitride top layer is about 10 nm and covers the substrate conformally. 13 The QCM signal is sensitive to the total mass coupled to the sensor surface. 14,15 Monitoring the dissipation of the signal provides information about the rigidity of this mass.…”

“…The LSPR field is most enhanced around sharp features; 21 in our case of thin nanodiscs we expect a cylindrical symmetrical field which is strongest at the outer rim. 13 The outer rim is the main contributor to the total signal even before considering field strength. The combined effect implies the LSPR signal is mostly representative for the SLB and SAv coverage on the outer rim of the nanodisc.…”

“…The presence of gold nanodiscs on the sensor surface does not affect SLB formation. 13 SLBs can form on strongly curved surfaces such as 110 nm diameter silica nanoparticles 22 and inside 75 nm diameter cylindrical pores. 23 Mornet et al have shown that the curved SLB follows the shape of the surface faithfully, even in the case of strong curvature.…”

“…Figure a schematically shows a QCM sensor chip containing gold nanodiscs for LSPR that are covered with silicon nitride. The nanodiscs have a thickness of ∼20 nm; the silicon nitride top layer is about 10 nm and covers the substrate conformally …”

“…The gold nanodiscs determine the shape of the LSPR field. The LSPR field is most enhanced around sharp features; in our case of thin nanodiscs we expect a cylindrical symmetrical field which is strongest at the outer rim . The outer rim is the main contributor to the total signal even before considering field strength.…”