Double-sided coordination assembly via a two-step ligand exchange reaction was introduced to synthesize superparamagnetic poly(styrene-co-acrylic acid)/Fe3O4/polyacrylic acid (P(St-AA)/Fe3O4/PAA) composite microspheres for the first time. In the two-step ligand exchange reaction, the coordination interaction of carboxyl groups with the iron replaced the hydrogen bonding between triethylene glycol (TEG) and the Fe3O4 nanoparticles, resulting in the attachment of the Fe3O4 nanoparticles onto the surface of P(St-AA) colloidal template and the coating of monomeric AA onto the surface of Fe3O4 nanoparticles. The obtained P(St-AA)/Fe3O4/PAA composite microspheres showed excellent uniformity, high saturation magnetization, stability and efficient protein separation capacity. The equilibrium adsorption capacity of P(St-AA)/Fe3O4/PAA microspheres for lysozyme was as high as 1800 mg g−1. Functionalized with nitrilotriacetate-Ni2+ (NTA-Ni2+), such composite microspheres could efficiently and selectively capture polyhistidine-tagged glutathione-S-transferase (His-tagged-GST) from cell lysate.
