An exclusive focus to date was on using HAuCl4 as precursor for this SF synthesis . It is found here that the use of AuCl does not lead to suitable results due to the limited solubility of AuCl in water (see details in SI). However, the use of AuCl3 is possible (although the solubility of AuCl3 in water is less than for HAuCl4). The optimal NaOH/Au molar ratio to obtain small size NPs is now around 3 which can be expected from the equations of the gold precursor reduction, as detailed in SI. The size obtained for the related sample E is around 16 nm. Is it observed from the UV-vis data in Figure that the overall yield, estimated by the absorbance at 400 nm (A400) is however lower when this precursor is used.