HEPES-involved hydrothermal synthesis of Fe3O4 nanoparticles and their biological applicationElectronic supplementary information (ESI) available. See DOI: 10.1039/c4ra12536c

A simple one-step hydrothermal route was developed for the synthesis of magnetite (Fe 3 O 4 ) nanoparticles in HEPES solution, using FeCl 2 as the Fe( ii ) precursor. It was found that HEPES played an important role in the fabrication of Fe 3 O 4 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 Fe 3 O 4 nanomaterials was also discussed. In the reaction system, the influence of inorganic anions on the morphologies of Fe 3 O 4 nanostructures was also investigated. The as-synthesized spherical Fe 3 O 4 nanoparticles with a concentration of 5-100 μg 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/Fe 3 O 4 and Au/Fe 3 O 4 nanocomposites were successfully synthesized by a two-step method, which showed excellent antibacterial properties against S. aureus . Furthermore, the Ag/Fe 3 O 4 and Au/Fe 3 O 4 nanocomposites could be recycled and reused due to their superparamagnetic properties and retained their antibacterial activities. Magnetic Fe 3 O 4 -based nanoparticles with good biocompatibility and excellent antibacterial properties against S. aureus were successfully synthesized by a HEPES-involved method.