Controllable synthesis of amine-functionalized Fe3O4 polyhedra for lipase immobilization

Abstract

We developed an efficient strategy to synthesize Fe₃O₄ truncated cubes, rhombic dodecahedra and octahedra with exposed {100}/{110}, {110} and {111} facets, respectively. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) spectra indicated that the Fe₃O₄ polyhedra were functionalized with a –NH₂ group. Magnetic measurements revealed that the prepared products have a high saturation magnetization and low coercive force. Because of the magnetic nature and amine-functionalized surfaces, the as-synthesized Fe₃O₄ polyhedra were employed as ideal magnetic carriers for lipase immobilization. Bradford protein assays indicated that the lipase loading amounts on Fe₃O₄ truncated cubes, rhombic dodecahedra and octahedra were 174.7, 175.6 and 175.8 mg of protein per g, respectively. Thermal stability tests revealed that the lipase immobilized on Fe₃O₄ octahedra was bound with great efficiency preserving the high catalytic activity and amplifying the stability. Reusability assays indicated that the lipase immobilized on Fe₃O₄ octahedra can be reused 4 times without a marked loss of catalytic activity (<8%). This work demonstrated that the prepared Fe₃O₄ octahedra were more stable and had promising applications in biological fields.