Ultrapure water (ELGA PURELAB Plus UV) with electrical resistivity 18.2 MΩ.cm was used in this work and all the references to water in the rest of this article should normally be taken to mean this quality of water. Three stock dispersions were prepared by diluting the supplied Au NP colloids by water and the respective concentration series were prepared by further diluting these stock dispersions by ultrapure water. The stock dispersions were prepared by keeping the total approximate surface area of 30 nm and 50 nm NPs in each stock dispersion equal by adopting the crude assumptions that the NPs were all spheres and all the Au NPs had the diameter of 10 nm (NP10), 30 nm (NP30) and 50 nm (NP50) for the respective samples. The concentration of NP10, under the same assumption, was five times the concentration that would have been needed to keep the surface area identical to the cases for NP30 and NP50. The concentration series for each of the three batches of Au NPs comprised of 20%, 40%, 60%, 80% and 100% (stock) strength, volume by volume, as calculated against the stock dispersions.