BSA Adsorption and Immobilization onto Charged Monodisperse Polymer Nanoparticles

Abstract

Controlling the behavior of adsorbed and immobilized proteins is essential for protein purification and a wide range of applications, including biosensors, biocatalysis and biomedical devices. In this study, monodisperse polymer particles were synthesized by soap free emulsion polymerization and the surface functional groups were directly introduced as a monomer or chemically modified with epoxy groups to enable protein immobilization through covalent bonding. Three kinds of surface charged particles having cationic, anionic, or both, groups were synthesized and characterized. Bovine serum albumin (BSA) was selected as a model protein to study the effect of pH of a buffer solution containing protein on the adsorption and immobilization amount. Protein adsorption was found to be strongly affected by pH and matching of the global protein and polymer particle charges, respectively. When pH was below the pI of either protein (pH 3.8), negatively charged polymer particles were found to adsorb a high amount of proteins. At maximum surface coverage of BSA on negatively charged polymer particles at pH 3.8 and after subsequent rinsing of the BSA-polymer particle complex with phosphate buffer (pH 7), ~50% of BSA was desorbed. Therefore, 50% of BSA was adsorbed by ionic interaction and the remaining fraction was immobilized covalently at pH 3.8. The remaining immobilized fraction was sufficient to completely shield the anionic charge of the polymer particles. Fluorescence spectroscopy suggests that at maximum immobilized amounts, the conformation of immobilized BSA appears to be the same as in aqueous solution.