Abstract
We used two-photon excitation fluorescence correlation spectroscopy (FCS) and neutron reflectometry to study in situ the effect of salt concentration on the degree of protein binding to polyelectrolyte brushes. The binding of bovine serum albumin (BSA) to poly(acrylic acid) (PAA) brushes was characterized at neutral pH values where both the protein and the brushes carry a negative charge. Spherical PAA brush particles were used in the FCS experiments, whereas a planar PAA brush served as protein substrate in the neutron reflectometry experiments. It has been found that BSA binds strongly to both the spherical and the planar PAA brushes under electrostatic repulsion at low ionic strength. The BSA volume fraction profile, as determined from the neutron reflectivities, indicates a deep penetration of the BSA molecules into the PAA brush. However, the analysis of the FCS data reveals that the protein affinity of the spherical PAA brush particles decreases drastically when increasing the concentration of sodium chloride to a few 100 mM. This observation is in line with the measured neutron reflectivities of the planar PAA brush. The reflectivity curve obtained in the absence of protein is virtually overlapping with that measured when the PAA brush is in contact with a BSA solution but containing 500 mM sodium chloride which suggests protein resistance of the planar PAA brush at this elevated salt concentration. The results of this study provide evidence for a new kind of protein-resistant interfaces. Whereas protein binding to the PAA brush is likely to be dominated by the release of counterions, this driving force vanishes as the ionic strength of the solution is raised and protein molecules are repelled from the interface by steric interactions. In a general view, the “switching” of the protein affinity of a PAA brush by varying the ionic strength of the protein solution over a relatively small range may appear to be useful for biotechnological applications.
Highlights
The adsorption ofprotein molecules at interfaces is one of the most interesting subjects in biophysical research, as it is the basis for a broad range of processes occurring in nature and biotechnology.[1 4]
We used two-photon excitation fluorescence correlation spectroscopy (FeS) and neutron reflectometry to study in situ the effect of salt concentration on the degree of protein binding to polyelectrolyte brushes
Spherical poly(acrylic acid) (PAA) brush particles were used in the Fes experiments, whereas a planar PAA brush served as protein substrate in the neutron reflectometry experiments
Summary
The adsorption ofprotein molecules at interfaces is one of the most interesting subjects in biophysical research, as it is the basis for a broad range of processes occurring in nature and biotechnology.[1 4]. As a rule that has emerged from numerous studies on protein adsorption carried out so far, one may generalize that all proteins adsorb at all interfaces. This rule originates largely in the heterogeneity of the protein surface and the conformational flexibility of the protein structure. The search for and the understanding ofprotein-resistant interfaces has attracted much research interest, since protein adsorption may have unfavourable consequences, such as biofilm formation on used contact lenses, biofouling of medical implants, or the attachment of mussels at ships.[3,10]. URL: http://nbn-resolving.de/urn:nbn:de:bsz:352-202164 a simple electrostatic screening, a PAA brush may be regarded as a new type of protein sorbent surface
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