Although the size distribution achieve here might seem larger than what can be reported in the literature, it is important to take into account that the present method is SF . In other words, there is no incentive to add chemicals to control the size. SF strategies are often considered impossible and far less explored than their surfactant-assisted counterparts, which leaves room for optimization. solvents in a RT process facilitates the processing of the NPs. It ultimately minimizes cost especially when it comes to scaling. (2) Few chemicals. Avoiding the use of several chemicals leads to a lower cost it comes to scale up. Avoiding having too many chemicals minimizes impurities which can lead to more reproducible syntheses . (3) Surfactant-free. Very well defined size controlled Au NPs obtained with additives are certainly conceptually interesting but are typically detrimental for catalysis . The protected NPs need to be activated, typically by heat treatments, which might induce size changes and therefore lead ultimately to poor size / composition control . Those post-treatments ultimately add costs specially upon up-scaling. (4) More control for size studies. A typical option to perform size effects studies is to use commercially available materials. which comes with the major disadvantage that the history of the materials is not known, and there is no size control per se given that one is limited by what is available from commercial suppliers . In conclusion, although the size control achieved here might appear relatively poor, it is important to keep in mind that it is actually a relatively fine size control given that no surfactants are used. As a comparison, in maybe the only alternative approach to obtain SF colloidal Au NPs which would be laser ablation, a centrifugation step is required to obtain relatively monodispersed samples . Here, a much simpler approach is proposed, that does not require any knowledge on lasers, and only simple equipment, that yet enables to produce in one step SF colloidal Au NPs with a relatively fine size control. The relevance of those materials to perform size effects study is illustrated and detailed in the next section. m 2 gAu -1