For kinetics studies, Amax corresponds to the maximum of absorption and is in most cases for the dataset here Amax=Aspr. Although at the initial stages of the reaction no clear spr signal is observed Amax is representative of the overall absorption since the spectra are almost straight lines. The value √𝐴 𝑚𝑎𝑥 3 when Amax=Aspr is proportional √𝑁 Samples. UV-vis spectra were acquired using a Shimadzu UV-1800 UV/Visible scanning spectrophotometer typically between 290 and 800 nm. As baseline, a solution with the corresponding amount of mQ water and the corresponding amount of ethanol or methanol and/or glycerol to what was used in the sample were preferred (no base, no HAuCl4). All samples were measured the day after synthesis (although it is important to note that the samples are stable for months, see Section 6 in SI). The samples are prepared directly in UV-vis cuvettes that were also used for those measurements.