New Insight Into the Size Tuning of Monodispersed Colloidal Gold Obtained by Citrate Method

We study the effect of citrate to gold molar ratio (X) on the size of citrated gold nanoparticles (AuNPs). This dependence is still a matter of debate for X $\ge$ 3 where the polydispersity is yet minimized. Indeed, there is no consensus between experiments proposed so far for comparable experimental conditions. Nonetheless, the sole available theoretical prediction has never been validated experimentally in this range of X. We show unambiguously using 3 techniques (UV-Vis spectroscopy, dynamic light scattering and transmission electronic microscopy), 2 different synthetic approaches (Direct, Inverse) and 10 X values for each approach that AuNPs' size decay as a monoexponential with X. This result is, for the first time, in agreement with the sole available theoretical prediction by Kumar et al. on the whole studied range of X.