3.4. Au Coating of Fe3O4 Nanoparticles

The magnetic Fe₃O₄ nanoparticles (average diameter 30 nm) were purchased by MERCK (catalog number 747327) and gold coated as follows. 100 μL of magnetic nanoparticles were added to a solution containing 50 mL of MilliQ water and sodium citrate (10 mg∙mL⁻¹) and they were heated until 90 °C with vigorous stirring. Once the temperature was reached, 50 μL of HAuCl₄·3H₂O (10 mg∙mL⁻¹) was added to the solution for four times every ten minutes. At this point the solution was let to cool down until it reached the room temperature keeping the same stirring. As a result of such a procedure a colloidal solution of 50 mL of Fe₃O₄@Au NPs was obtained.