Synthesis of Fe oxide Core/Au shell nanoparticles by iterative hydroxylamine seeding

Water-soluble, Au-coated magnetic Fe oxide nanoparticles with diameters ∼60 nm were synthesized by the reduction of Au³⁺ onto the surfaces of ∼9 nm diameter particles consisting of either γ-Fe₂O₃ or partially oxidized Fe₃O₄ via iterative hydroxylamine seeding. The morphology and optical properties of the core/shell particles are dependent on the quantity of deposited Au, while the magnetic properties remain largely independent of Au addition. The Au-coated particles exhibit a surface plasmon resonance peak that blue-shifts from 570 to 525 nm with increasing Au deposition. SQUID magnetometry reveals that particle magnetic properties are not affected by the overlayer of a moderately thick Au shell.