Protein Density Profile at the Interface of Water with Oligo(ethylene glycol) Self-Assembled Monolayers

Abstract

We determined the density profile of a high-molecular-weight globular protein (bovine serum albumin, BSA) solution at the methoxy tri(ethylene glycol)-terminated undecanethiol SAM/protein solution interface by neutron reflectivity measurements. Information about the interactions between oligo(ethylene glycol) (OEG)-terminated self-assembled monolayers (SAMs) and proteins is derived from the analysis of the structure of the solid-liquid interface. The fitting results reveal oscillations of the protein density around the bulk value with decaying amplitude on a length scale of 4 to 5 nm. The amplitude, phase, period, and decay length are found to vary only slightly with temperature and the ionic strength of the protein solution. Adsorption is reversible within the limits of detection, which suggests that the hydrated ethylene glycol surface inhibits the protein from unfolding and irreversible bonding. The insensitivity of BSA adsorption toward the ionic strength of the solution contrasts with observations in surface force experiments with a fibrinogen-coated AFM tip, where electrostatic repulsion dominates theprotein/OEG SAM interaction. As reported previously, irreversible BSA adsorption takes place below 283 K, which we interpret as indicative of the presence of dynamic effects in the protein resistance of short-chain OEG-terminated surfaces.

Two-dimensional enzyme diffusion in laterally confined DNA monolayers

“…Despite that this semiquantitative model provides a plausible explanation of our findings, and additional effects may (or should) be considered to further extend the implications of our work: the 2D diffusion could be favoured by reversible enzyme absorption on the ethylene-glycol-terminated molecules on the surface near the SW, as suggested by a recent neutron reflectivity study of Schreiber and co-workers 45 . This effect may help increase the enzyme concentration in the area surrounding the matrices (that is, at the matrices sides) and, similarly, the enzymes would be trapped within the matrix while they diffuse two-dimensionally.…”

“…The abovementioned work, which was based, however, on protein concentrations much higher than in our case, demonstrates an oscillating protein density profile, right above a protein-depleted hydration layer, adjacent to the top-oligo-ethylene-glycol-3 (TOEG3), which inhibits the protein from unfolding and irreversible bonding. Protein/ surface interactions are, in general, complex phenomena that depend on several parameters, including local electrostatic interactions and diffusion 45 . In contrast to Schreiber and co-workers 45 , Grunze and co-workers 46 probed the resistance to protein adsorption on TOEG3 SAMs on gold surfaces by scanning force microscopy using negatively charged and hydrophobic AFM tips to mimic a protein in solution.…”

“…Protein/ surface interactions are, in general, complex phenomena that depend on several parameters, including local electrostatic interactions and diffusion 45 . In contrast to Schreiber and co-workers 45 , Grunze and co-workers 46 probed the resistance to protein adsorption on TOEG3 SAMs on gold surfaces by scanning force microscopy using negatively charged and hydrophobic AFM tips to mimic a protein in solution. Their force-distance measurements showed that electrostatic effects are important factors for the interaction of proteins on the TOEG3 on gold, and that this interaction markedly changes on slight changes in the molecular orientation of TOEG3 molecules on different metal surfaces, in a manner that is difficult to account for using a simplified model.…”

Molecular-scale surface structures of oligo(ethylene glycol)-terminated self-assembled monolayers investigated by frequency modulation atomic force microscopy in aqueous solution

“…[17][18][19][20] In the meanwhile, microscopic studies on the surface structures of OEG-SAMs have been very limited. In particular, molecular-scale arrangements of domain boundaries, etch pits and defects of an OEG-SAM have not been well understood.…”

Water Soluble Responsive Polymer Brushes

“…The field of protein resistant surfaces is very active; and whilst these materials cannot be described as responsive they can be combined with other polymers to enable the system to resist non-specific protein absorption that would over a short space of time in a biological environment cover the whole layer reducing the surface functionality of the overall film. For further background reading on this subject please refer to the following papers highlighted on this subject [38][39][40][41].…”