The effect of coadsorption on the conformational arrangement of human plasma fibronectin (Fn) was studied for mixtures with human serum albumin (HSA) adsorbed onto mildly hydrophilic gold substrates. Quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM) were used to measure the mass uptake, thickness, viscoelastic behaviour, and morphology of the adsorbed protein adlayers. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed to determine the composition of binary protein adlayers, taking advantage of the principal component analysis (PCA) technique of ToF-SIMS data. Thus, the ToF-SIMS results provided the particular fragmentation patterns of the two proteins, showing that the resulting mixed protein layers were predominantly formed by Fn molecules, even for binary solutions with high molar fraction of HSA. The conformational arrangement of the Fn molecules was studied by combining ToF-SIMS and QCM-D techniques. ToF-SIMS data allowed the identification of Type I–Type III modules of Fn and showed that pure Fn layers predominantly expose Type III modules, while coadsorbed Fn/HSA layers predominantly expose Fn Type I epitopes. QCM-D was employed to measure the relative uptake of a polyclonal antibody (anti-Fn) to the 4F15F1 binding domain in the Fn Hep I fragment in Type I modules, showing that pure Fn adlayers have a reduced anti-Fn binding capacity, as expected for Type I modules buried within the adlayers, while coadsorbed Fn layers bind more efficiently the anti-Fn, as the concerned Type I module is predominantly exposed at the layer surface. The results overall demonstrated that coadsorption of Fn and HSA onto mildly hydrophilic gold substrates prompts Fn to undergo a closed-to-open conformational switch.
The lack of methodologies which enable us to measure forces acting between nanomaterials is one of the factors limiting the full comprehension of their behavior and their more effective exploitation in new devices. Here we exploit the irreversible adsorption of surfactant-decorated nanoparticles at the air/water interface to investigate interparticle forces and the effect of the surfactant structure on them. We measured the interparticle repulsive forces as a function of the modulation of the interparticle distance by simultaneously performing compression isotherms and the grazing incidence small-angle X-ray scattering (GISAXS) structural characterization of the monolayers at water-vapor interfaces. Our results demonstrate that the short-range interparticle forces are strongly affected by the presence of the organic ligands, which are shown to be able to influence the interparticle repulsions even when added in micromolar amounts. In particular, we demonstrate the predominant steric nature of short-range forces, which are accounted for in terms of the compression-induced stretched-to-coiled conformational transition of the ligand hydrophobic tail.
