Synthesis of Biocompatible, Mesoporous Fe₃O₄ Nano/Microspheres with Large Surface Area for Magnetic Resonance Imaging and Therapeutic Applications

This article reports the fabrication of mesoporous Fe₃O₄ nano/microspheres with a high surface area value (163 m²/g, Brunauer−Emmett−Teller) and demonstrates their use for drug loading, release, and magnetic resonance imaging (MRI). These monodispersed, mesoporous Fe₃O₄ nano/microspheres with controllable average sizes ranging from 50 to 200 nm were synthesized using a Fe₃O₄/poly(acrylic acid) hybrid sphere template and subsequent silica shell formation and removal. We found that the SiO₂ coating is a crucial step for the successful synthesis of uniform mesoporous Fe₃O₄ nano/microspheres. The as-synthesized mesoporous Fe₃O₄ nanospheres show a high magnetic saturation value (M_s = 48.6 emu/g) and could be used as MRI contrast agents (r₂ = 36.3 s⁻¹ mM⁻¹). Trypan blue exclusion and MTT assay (see Supporting Information) cytotoxicity analyses of the nanospheres based on HepG2 and MDCK cells showed that the products were biocompatible, with a lower toxicity than lipofectamine (positive control). Hydrophilic ibuprofen and hydrophobic zinc(II) phthalocyanine drug loading into mesoporous Fe₃O₄ nanospheres and selected release experiments were successfully achieved. The potential use of mesoporous Fe₃O₄ nanospheres in biomedical applications, in light of the nano/microspheres’ efficient drug loading and release, MRI, and low cytotoxicity, has been demonstrated. It is envisaged that mesoporous Fe₃O₄ nanospheres can be used as drug carriers and MRI contrast agents for the reticuloendothelial system; they can also be delivered locally, such as via a selective catheter.