Nanomaterials, e.g. nanoparticles (NPs) present a set of unique features relevant for applications as broad as medicine, sensing or catalysis. It is well established that size, shape and/or composition are important parameters to control to make the most of the nanomaterial properties. Various routes have been reported to prepare NPs, for instance for metallic nanomaterials such as gold-based NPs that are key for several nanotechnologies. In particular, wet chemical syntheses are a popular approach, where a molecular precursor containing one atom of the desired metal is reduced in the liquid phase to NPs made of several hundreds or thousands of atoms. Nevertheless, the quest for optimal syntheses to make the most of every metal atom, especially relevant in the case of expensive materials such as gold (Au), is still ongoing. Despite several decades of studies, several challenges remain for the controlled synthesis of various metal NPs. First, most syntheses require several chemicals playing the roles of solvent, reducing agents and/or stabilizers. A rational selection of the several chemicals typically needed remains the results of trials-and-errors, due to a lack of a deep understanding on the role of each chemical. Second, the selection of the right parameters such as concentrations, temperature, duration of the syntheses etc. are also often the results of (extensive) parametric studies. In most cases, the equipment and conditions required to perform the synthesis -e.g. autoclaves, high temperatures, high pressures, inert conditions, etc. -allows only few experiments to be performed in a day. The screening of the large parametric spaces available is therefore relatively time-, manpower-and resource-consuming as well as waste-generating. As a consequence, defining, refining and tuning the right set of parameters to achieve a fine control over the NP properties such as size, structure or composition, remains an everlasting and daunting task. This challenge explains in part why state-of-the-art colloidal syntheses of Au NPs, such as the Turkevich-Frens synthesis reported 70 years ago, are still being refined. As a third challenge, the increasing awareness on the relevance and the need for sustainable methods to produce NPs to comply with the principles of Green Chemistry is encouraging to (re)focus classical approaches to prepare NPs towards more green strategies, e.g. preferring room temperature (RT) syntheses, the use of benign solvents and/or fewer chemicals, moving away from most of the chemicals typically used to date that are harmful and/or derived from fossil fuels. A promising emerging strategy to provide new insights into NP formation and comply with the principles of Green Chemistry is to exploit the potential of surfactant-free NPs, ideally performed at low temperature in aqueous media. The definition of surfactant-free NPs can be subject to debate. Following a definition recently proposed, we consider that a colloidal synthesis is surfactant-free if no chemicals used for the synthesis, other than the metal precursor, has a molar mass over 100 g mol -1 . Using fewer and simpler chemicals, surfactant-free syntheses, have the potential to bring new insights into NP formation and stabilization, provided reproducible syntheses can be developed and detailed protocols reported. Surfactant-free NPs are also directly relevant for catalysis, energy conversion, sensing, etc., where clean NP surfaces are needed.