Seed-Mediated Synthesis of Gold Nanoparticles of Controlled Sizes To Demonstrate the Impact of Size on Optical Properties

Gold (Au) nanoparticles of varying sizes were synthesized during an outreach activity to introduce students to the size-dependent optical properties of nanomaterials. For the fabrication of Au nanoparticles of varying sizes, a seeded growth method was employed. In the first part of the activity, students performed the Frens method to obtain Au seeds. Students then used these seeds in the second part to conduct a seed-mediated synthesis, and obtained Au nanoparticles of a wide size range. The size differences in the particles were evident by eyesight due to color changes in the nanoparticle solutions. In addition to observations made about color, the nanoparticles were characterized using UV–vis spectroscopy, and a red shift in the peak wavelength of the extinction spectra of the Au nanoparticles was observed when nanoparticles were grown larger in size. This activity demonstrates a straightforward approach to seed-mediated nanoparticle growth and is applicable to both high school and undergraduate students.