Hierarchical Fe₃O₄@Ni _x SiO _y microspheres for affinity separation of His-tagged proteins

Hierarchical Fe₃O₄@Ni _x SiO _y microspheres (MSs) are synthesized via a facile hydrothermal method, using Fe₃O₄@SiO₂ MSs as template. The prepared Fe₃O₄ cores present spherical shape and have a mean diameter of 500 nm, and the Ni _x SiO _y shell with thickness of 50 nm was composed of a large number of sheets. The Fe₃O₄@Ni _x SiO _y MSs are easily manipulated by an external magnetic force. By taking advantages of the high affinity of Ni²⁺ on the shell surface toward histidine-tagged (His-tagged) proteins, the Fe₃O₄@Ni _x SiO _y MSs can be applied to enrich and magnetically separate His-tagged proteins directly from the mixture of lysed cells. Research results indicated that the Fe₃O₄@Ni _x SiO _y MSs presented negligible nonspecific protein adsorption and high protein binding ability. These MSs with a high binding capacity of 14.6 mmol g⁻¹ are much higher than that of commercial microbeads at only 10–12 mg g⁻¹. Their specificity and affinity toward His-tagged proteins can be remained after four times recycling. The obtained Fe₃O₄@Ni _x SiO _y MSs are especially suitable for rapid purification of His-tagged proteins.