Characterization of a planar poly(acrylic acid) brush as a materials coating for controlled protein immobilization.
The adsorption of two different proteins at a planar poly(acrylic acid) (PAA) brush was studied as a function of the ionic strength of the protein solutions applying total internal reflection fluorescence (TIRF) spectroscopy. Planar PAA brushes were prepared with a grafting density of 0.11 nm(-2) and were characterized using X-ray reflectometry. Hen egg-white lysozyme and bovine serum albumin (BSA) were used as model proteins, which have a net positive and negative charge at neutral pH-values, respectively. It has been found that both proteins adsorb strongly at a planar PAA brush at low ionic strength. Whereas lysozyme interacts with a PAA brush under electrostatic attraction at neutral pH-values, BSA binds under electrostatic repulsion at pH > 5. Even at pH = 8, significant amounts of BSA are adsorbed to a planar PAA brush. In addition, the reversibility of BSA adsorption has been characterized. Dilution of a BSA solution leads to an almost complete desorption of BSA from a PAA brush at short contact times. When the ionic strength of the protein solutions is increased to about 100-200 mM, a planar PAA brush appears largely protein-resistant, regardless of the protein net charge. The results of this study indicate that the salt-dependent protein affinity of a PAA brush represents a unique effect that must be explained by a novel protein-binding mechanism. On the basis of a recent model, it is suggested that a release of counterions is the most probable driving force for protein adsorption at a PAA brush. In a general view, this study characterizes a planar PAA brush as a new materials coating for the controlled immobilization of proteins whose use in biotechnological applications appears to be rewarding.
Universität Dortmund, Fachbereich Chemie, Otto-Hahn-Strasse 6, D-44227 Dortmund, Germany.
Oliver
O
Hollmann
Claus
C
Czeslik
D000180:Acrylic Resins / Q000737:chemistry*; D000327:Adsorption; D000818:Animals; D002417:Cattle; D002645:Chickens; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D009113:Muramidase; D009994:Osmolar Concentration; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000737:chemistry*
D000180:Acrylic Resins; D012710:Serum Albumin, Bovine; C006903:carbopol 940; D009113:Muramidase