Double-sided coordination assembly: superparamagnetic composite microspheres with layer-by-layer structure for protein separation

Abstract

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.