Magnetic Separation of Antibodies with High Binding Capacity by Site-Directed Immobilization of Protein A-Domains to Bare Iron Oxide Nanoparticles

The demand for purified antibodies is ever-rising. This study presents a nanoparticle-based material for efficient magnetic separation of immunoglobulin G (IgG) with high binding capacity. The characteristics include: (i) Cost-effective bare iron oxide nanoparticles are used as the solid phase on which optimized protein A-based ligands are directly immobilized. An additional chemical modification or activation is not needed. (ii) Oriented immobilization of the ligands is promoted using a C-terminal peptide tag, containing amino acids with an affinity for iron oxide. (iii) The immobilized ligand consists of eight polymerized B-domains of Protein A. This affinity adsorbent for antibody capture allows a recovery of up to 418 mg IgG per gram of particle, which exceeds the state of the art of magnetic nanoparticles as well as microparticles. Particles with a lower ligand density show a higher percentage recovery of IgG, which allows for a cost-effective design of the adsorbent. Furthermore, the selectivity of the immobilized ligand is shown by means of purification of rabbit polyclonal IgG using rabbit serum.