Adsorption of the Protein Bovine Serum Albumin in a Planar Poly(acrylic acid) Brush Layer As Measured by Optical Reflectometry

• Published in: Langmuir Vol. 24; no. 13; pp. 6575 - 6584
• Main Authors: de Vos, Wiebe M, Biesheuvel, P. Maarten, de Keizer, Arie, Kleijn, J. Mieke, Cohen Stuart, Martien A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.07.2008
• Subjects: Acrylic Resins - chemistry; Adsorption; Animals; aqueous-solution; Cattle; charge regulation; Chemistry; Chemistry Techniques, Analytical; chloride; Colloidal state and disperse state; complexes; electrostatic interactions; Exact sciences and technology; General and physical chemistry; Hydrogen-Ion Concentration; Interfaces: Adsorption, Reactions, Films, Forces; Optics and Photonics; Osmolar Concentration; particles; Salts; Serum Albumin, Bovine - chemistry; spectroscopy; spherical polyelectrolyte brushes; Surface physical chemistry; Experimental data; Critical value; Bovine; Excluded volume; Acrylic acid; Chain length; Prediction; Polymer; Serum albumin; Density; Grafting; Protein; Polyelectrolyte; Vertebrata; Mammalia; Adsorption; Ionic strength; Distribution; Reflectometry; pH; Models; Artiodactyla; Electrostatic potential; Ungulata
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la8006469

The adsorption of bovine serum albumin (BSA) in a planar poly(acrylic acid) (PAA) brush layer has been studied by fixed-angle optical reflectometry. The influence of polymer length, grafting density, and salt concentration is studied as a function of pH. The results are compared with predictions of an analytical polyelectrolyte brush model, which incorporates charge regulation and excluded volume interactions. A maximum in adsorption is found near the point of zero charge (pzc) of the protein. At the maximum, BSA accumulates in a PAA brush to at least 30 vol %. Substantial adsorption continues above the pzc, that is, in the pH range where a net negatively charged protein adsorbs into a negatively charged brush layer, up to a critical pH value. This critical pH value decreases with increasing ionic strength. The adsorbed amount increases strongly with both increasing PAA chain length and increasing grafting density. Experimental data compare well with the analytical model without having to include a nonhomogeneous charge distribution on the protein surface. Instead, charge regulation, which implies that the protein adjusts its charge due to the negative electrostatic potential in the brush, plays an important role in the interpretation of the adsorbed amounts. Together with nonelectrostatic interactions, it explains the significant protein adsorption above the pzc.