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.