through the parameter Aspr/A450, is suitable to assess the relative size of the NPs. As confirmed by STEM and as expected from the literature, the lower the Aspr/A450 ratio, the smaller the NPs for spherical NPs . A first alternative strategy reported here to achieve size control is to induce the synthesis in different ways. Since the controlled addition of the HAuCl4 under proper mixing is a likely key factor for the successful synthesis of the NPs , the synthesis was performed using sonochemistry (ultrasonic bath), stirring or manual shaking. In all cases small size NPs are obtained. A discussion of the effect of sonication is proposed in SI. Although a reproducible control on size is not simply achieved by sonication, this approach can lead to baches of very small size NPs ca. 5 nm (smaller than the smallest size reported typically for this SF approach) .