Ni2+-zeolite/ferrosphere and Ni2+-silica/ferrosphere beads for magnetic affinity separation of histidine-tagged proteins
Magnetic Ni2+-zeolite/ferrosphere and Ni2+-silica/ferrosphere beads (Ni-ferrosphere beads – NFB) of a core–shell structure were synthesized starting from coal fly ash ferrospheres having diameters in the range of 0.063–0.050 mm. The strategy of NFB fabrication is an oriented chemical modification of the outer surface preserving the magnetic core of parent beads with the formation of micro–mesoporous coverings. Two routes of ferrosphere modification were realized, such as (i) hydrothermal treatment in an alkaline medium resulting in a NaP zeolite layer and (ii) synthesis of micro–mesoporous silica on the glass surface using conventional methods. Immobilization of Ni2+ ions in the siliceous porous shell of the magnetic beads was carried out via (i) the ion exchange of Na+ for Ni2+ in the zeolite layer or (ii) deposition of NiO clusters in the zeolite and silica pores. The final NFB were tested for affinity in magnetic separation of the histidine-tagged green fluorescent protein (GFP) directly from a cell lysate. Results pointed to the high affinity of the magnetic beads towards the protein in the presence of 10 mM EDTA. The sorption capacity of the ferrosphere-based Ni-beads with respect to GFP was in the range 1.5–5.7 mg cm−3.