By tuning the method to induce the synthesis, precursor grade, and/or type of precursor, a relative fine size control over Au NPs with size 4.9 ± 1.4, 9.4 ± 3.1, 9.4 ± 3.1, 12.8 ± 5.6, 15.0 ± 5.8 and 21.6 ± 7.7 nm (samples A-F, respectively) was achieved by a simple RT SF colloidal synthesis requiring only a gold precursor, water, an alcohol, and moderately alkaline conditions.