Synthesis and optical properties of size-controlled gold nanoparticles

Au nanoparticles (NPs) of various sizes were synthesized by controlling the NP growth process. When the ratio of the HAuCl₄ and NaBH₄ solution concentrations was controlled, the experimental results showed that the average Au NP size decreased as the HAuCl₄ concentration of the seed solution increased, owing to the increase in the number of Au seeds. The activity of the seed solution decreased as the additive volume of the HAuCl₄ solution increased, resulting in the formation of large Au seeds. At low seed solution additive volumes, the peak absorbance wavelength and average size of the Au NPs decreased rapidly as the seed solution additive volume increased. The final size of the Au NPs with negatively charged Au seeds was relatively large since the size of the negatively charged Au seeds was relatively large. In addition, it was easier for the negatively charged seed solution to absorb Au atoms in the positively charged growth solution. A high ascorbic acid concentration was beneficial for improving the production of Au NPs. The average size of the Au seeds added to the growth solution increased gradually with the number of NPs grown, which resulted in an increase in the average Au NP size.