Subsurface Influence on the Structure of Protein Adsorbates as Revealed by in Situ X-ray Reflectivity

Abstract

The adsorption process of proteins to surfaces is governed by the mutual interactions among proteins, the solution, and the substrate. Interactions arising from the substrate are usually attributed to the uppermost atomic layer. This actual surface defines the surface chemistry and hence steric and electrostatic interactions. For a comprehensive understanding, however, the interactions arising from the bulk material also have to be considered. Our protein adsorption experiments with globular proteins (α-amylase, bovine serum albumin, and lysozyme) clearly reveal the influence of the subsurface material via van der Waals forces. Here, a set of functionalized silicon wafers enables a distinction between the effects of surface chemistry and the subsurface composition of the substrate. Whereas the surface chemistry controls whether the individual proteins are denatured, the strength of the van der Waals forces affects the final layer density and hence the adsorbed amount of proteins. The results imply that van der Waals forces mainly influence surface processes, which govern the structure formation of the protein adsorbates, such as surface diffusion and spreading.

Macroscale adhesion of gecko setae reflects nanoscale differences in subsurface composition

“…Recently, a similar influence was detected on the adsorption kinetics of proteins [11][12][13] and the adhesion of bacteria [14]. These experiments used materials whose contribution to the potential had been tuned by means of surface stratification.…”

“…All wafer types were characterized using atomic force microscopy, ellipsometry and water contact angle measurements (cf. table 2; further characterization data available in [13,34]). Immediately prior to the experiments, the substrates were cleaned by immersing them subsequently into ethanol and acetone (5 min each) in a ultrasonic bath and rinsing them for 30 min in boiling DI water.…”

Experimental approach towards the water contact angle value on the biomaterial alloy Ti6Al4V

“…The influence of van der Waals interactions from the bulk material to the top surface can be also transferred to the contact angle information, since van der Waals forces range over tens of nanometers [23]. Hähl et al [24] studied the adsorbed layer of globular proteins on silicon wafers with silicon oxide layers of different thickness. They proved that the characteristics of the adsorbed layers of proteins were affected not only by a few top layers of atoms on the surface, but also were sensitive to the van der Waals forces from the subsurface layers.…”

A neutron reflection study of adsorbed deuterated myoglobin layers on hydrophobic surfaces

“…Moreover, Evers et al shows a change of the denaturation of lysozyme with salt concentration leading to an improvement of the adsorption at high salt concentration [53]. Hahl et al [54] have also shown by X-ray reflectivity that, at low concentration (0.1 mg/ml), a-amylase, bovin serum albumin (BSA) and lysozyme are denaturated on hydrophobic surfaces and not denaturated on hydrophilic SiO 2 . Lu et al [41] also studied lysozyme adsorption on OTS as function of pH at a low protein concentration of 0.03 mg/ml.…”