HEPES-involved hydrothermal synthesis of Fe3O4 nanoparticles and their biological application

A simple one-step hydrothermal route was developed for the synthesis of magnetite (Fe3O4) nanoparticles in HEPES solution, using FeCl2 as the Fe(II) precursor. It was found that HEPES played an important role in the fabrication of Fe3O4 nanoparticles, where HEPES could act as a weak antioxidant to prevent the complete oxidation of Fe(II) to Fe(III). The possible formation mechanism of HEPES-coated Fe3O4 nanomaterials was also discussed. In the reaction system, the influence of inorganic anions on the morphologies of Fe3O4 nanostructures was also investigated. The as-synthesized spherical Fe3O4 nanoparticles with a concentration of 5-100 mu g mL(-1) exhibited nontoxicity towards HUVEC normal cells, indicating their potential application in biology. Combining the preparation of Ag and Au nanoparticles in HEPES solution, Ag/Fe3O4 and Au/Fe3O4 nanocomposites were successfully synthesized by a two-step method, which showed excellent antibacterial properties against S. aureus. Furthermore, the Ag/Fe3O4 and Au/ Fe3O4 nanocomposites could be recycled and reused due to their superparamagnetic properties and retained their antibacterial activities.