Characterization of a Planar Poly(acrylic acid) Brush as a Materials Coating for Controlled Protein Immobilization

• Published in: Langmuir 2006-03, Vol.22 (7), p.3300-3305
• Main Authors: Hollmann, Oliver, Czeslik, Claus
• Format: Article
• Language: English
• Subjects: Acrylic Resins - chemistry; Adsorption; Animals; Cattle; Chemistry; Chickens; Exact sciences and technology; General and physical chemistry; Hydrogen-Ion Concentration; Models, Chemical; Muramidase; Osmolar Concentration; Protein Binding; Serum Albumin, Bovine - chemistry; Surface physical chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la053110y

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.