Preparation of silica coated cobalt ferrite magnetic nanoparticles for the purification of histidine-tagged proteins

Surface modified cobalt ferrite (CoFe₂O₄) nanoparticles containing Ni–NTA affinity group were synthesized and used for the separation of histidine tag proteins from the complex matrices through the use of imidazole side chains of histidine molecules. Firstly, CoFe₂O₄ nanoparticles with a narrow size distribution were prepared in an aqueous solution using the controlled co-precipitation method. In order to obtain small CoFe₂O₄ agglomerates, oleic acid and sodium chloride were used as dispersants. The CoFe₂O₄ particles were coated with silica and subsequently the surface of these silica coated particles (SiO₂–CoFe₂O₄) was modified by amine (NH₂) groups in order to add further functional groups on the silica shell. Then, carboxyl (–COOH) functional groups were added to the SiO₂–CoFe₂O₄ magnetic nanoparticles through the NH₂ groups. After that Nα,Nα–Bis(carboxymethyl)-l-lysine hydrate (NTA) was attached to carboxyl ends of the structure. Finally, the surface modified nanoparticles were labeled with nickel (Ni) (II) ions. Furthermore, the modified SiO₂–CoFe₂O₄ magnetic nanoparticles were utilized as a new system that allows purification of the N-terminal His-tagged recombinant small heat shock protein, Tpv-sHSP 14.3.