Despite the absence of added stabilizers, the Au NPs colloids are stable for weeks as detailed in Figures and, where the UV-vis spectra of the as-prepared NPs and the UV-vis of the same batch after 3 months of storage at room temperature in a drawer are almost the same (the measurements were performed without homogenization of the sample). It is worth pointing that surfactant-free NPs prepared with 20-30 v.% are even stable for years as detailed elsewhere. While the stabilization mechanism of the Au NPs is still to be fully established, electrostatic interactions seem key and the contribution of species such as acetaldehyde (oxidation product of ethanol) cannot be ruled out. Figure . UV-vis spectra for a sample prepared with [18 v.% Et + 2 v.% Gly], 24 hours after the beginning of the synthesis (D1) or after 3 months (M3), as indicated. The samples were kept at room temperature in a drawer. Et: Ethanol; Gly: Glycerol.