Metrics. The Mie theory correlates various variables to the optical properties of Au NPs. UV-vis spectra of Au NPs results from a complex interplay between the properties of gold, nanoscale effects (such as size and shape) and interaction with the solvents and/or interactions between NPs and precursor. Due to their plasmonic properties (surface plasmon resonance, spr), several relevant parameters descriptive of the Au NPs can be retrieved: λspr, 42 A400, Aspr/A450, 42 A380/A800, all defined, detailed and summarized in Table in Supplementary Information (SI). Note that the relationships indicated are only true for certain conditions that are not always met in the experiments below (e.g. for low yields experiments or for too large NPs) but are convenient indicators of the properties of the Au NPs. The good correlation between λspr values and size retrieved by STEM is detailed elsewhere and documented in Figure .