2.3. Synthesis of Au-Fe3O4 NPs
The Au-Fe3O4 NPs were synthesized according to a previously
published method [22,25]. Firstly, we synthesized the Au NPs
as seeds. The following method was used: HAuCl4·3H2O (0.1 g,
0.25 mmol) was added to 10 mL tetralin and 1 mL oleylamine
(3 mmol) to form a red solution. The solution was heated at 75 ◦C
for 5 h and then cooled to room temperature. The Au particles were
separated by adding ethanol, centrifuged and then re-dispersed in
hexane. Secondly, Au-Fe3O4 NPs were prepared as follows: a solution
of 1 mL oleylamine (3 mmol), 1 mL oleic acid (3 mmol) and
20 mL octadecene was added to a three-neck flask, followed by
the addition of 2 mL hexane solution of Au NPs (20 mg/mL). The
mixed solution was heated at 120 ◦C for 50 min to remove hexane.
Then0.1 mL Fe(CO)5 was injectedunder anitrogenatmosphere. The
mixture was slowly heated to 240 ◦C and maintained at this temperature
for 40 min. The solution was cooled to room temperature
andstirredfor another 1 hto formFe3O4 NPsunder air.Iso-propanol
was added to the solution, which was separated by centrifugation
and re-dispersed in CHCl3.