The chemical synthesis was performed according to a previously reported protocol [36].
0.1 mol L−1 NaBH4 was added with stirring to an aqueous solution that contained 20 mL of 0.25 mmol L−1 HAuCl4 and 0.25 mmol L−1 trisodium citrate.
The AuNPs were characterized by TEM and UV–vis spectroscopy.