Protein immobilization and separation using anionic/cationic spherical polyelectrolyte brushes based on charge anisotropy

Abstract

Interactions between bovine serum albumin (BSA)/β-lactoglobulin (BLG) and spherical polyelectrolyte brushes (SPBs) were investigated by a combination of turbidimetric titration, dynamic light scattering (DLS), zeta potential measurement, and small angle X-ray scattering (SAXS) which revealed different behaviors, architectures, and phase states of pH dependent protein–SPB interactions. Binding energetics, affinity, and stoichiometry between BSA–BLG and SPBs were determined by isothermal titration calorimetry (ITC) to get further information concerning the interaction difference. The SPBs consist of narrowly distributed polystyrene core particles (ca. 80 nm in diameter) onto which linear chains of polyelectrolytes, either weak anionic poly(acrylic acid) (PAA) or weak cationic poly(2-aminoethyl methacrylate hydrochloride) (PAEMH), are grafted. For a particular protein (BSA or BLG), the binding stoichiometry, affinity, architecture, and phase state between proteins and anionic SPBs were significantly different from those for cationic SPBs. Significantly larger binding affinity and adsorbed amount were observed for BSA in anionic SPBs versus cationic SPBs, while opposite for BLG, which were explained in terms of different charge anisotropy of proteins. These findings lay the foundation for SPB applications in the separation and immobilization of different proteins.