Protein A and protein A/G coupled magnetic SiO₂ microspheres for affinity purification of immunoglobulin G

Protein A carrying magnetic, monodisperse SiO₂ microspheres [Mag(SiO₂)] with bimodal pore size distribution including both mesoporous and macroporous compartments were proposed as an affinity sorbent for IgG purification. Protein A was tightly bound onto the aldehyde functionalized-Mag(SiO₂) microspheres. The mesoporous compartment provided high surface area for protein A binding and IgG adsorption while the macropores made easier the intraparticular diffusion of protein A and IgG. The selection of relatively larger microspheres with high saturation magnetization allowed faster magnetic separation of affinity sorbent from the IgG isolation medium, less than 1min. With these properties, the proposed sorbent is an alternative to the common sorbents in the form of core-shell type, magnetic silica nanoparticles with more limited surface area and slower magnetic response. By using protein A attached-Mag(SiO₂) microspheres with the concentrations lower than 50mg/mL, IgG isolation from rabbit serum was performed with a purity higher than 95%, with an isolation yield comparable to commercial magnetic resins, and in shorter isolation periods. IgG could be also quantitatively isolated from rabbit serum with the sorbent concentrations higher than 50mg/mL. Successive IgG isolation runs indicated that no significant protein A leaching occurred from the magnetic matrix.