Optimization towards more sustainable syntheses. The opportunity to use a small amount of glycerol finally pushed us to investigate lower total contents of alcohols. Mixtures with a total amount of ca. 10 v.% and 5 v.% were considered. For the same reasons as those detailed above, a focus was on mixtures with higher ethanol contents than glycerol. Results are reported in Figures and-S16. Using 10 v.% ethanol, 8 v.% ethanol, 5 v.% ethanol or 3 v.% ethanol did not lead to stable colloids, no well-defined spr was observed and the results tend to be less reproducible as the ethanol content decreases, in agreement with the results presented above. Using 2 or 3 v.% glycerol also did not lead to stable colloids and the results tend to be more difficult to reproduce. However, the use of .% ethanol + 2 v.% glycerol] or [3 v.% ethanol + 2 v.% glycerol] leads to improved syntheses: more defined λspr peaks after 24 hours (compared to the case where 10 v.% or 5 v.% ethanol was used), smaller λspr values than if 2 v.% glycerol only was used. The Au NPs colloids are also more stable over time as detailed in the next section.