Here we report a fast and simple protocol for the synthesis of seedless Au nanoparticle (NP) colloidal solutions with sizes ranging between 4 and 150 nm in water. We also show in this study the failure to obtain Au NPs with diameter larger than 30–40 nm via citrate reduction, due to an increase in the polydispersity and the shape diversity of the final Au NPs. This result indicates the importance of new reducing agents in the production of Au NPs, especially for diameters above 40 nm