Determination of Gold Nanoparticle Sizes from Their Plasmon Resonance within the Optical Spectrum

Abstract

Nanoparticles have exciting properties that can be tailored by altering their size, density and shape. Several essential properties of the nanoparticles have been investigated for various applications. One such property strongly affected by the nanoparticle size is localised surface plasmon resonance (LSPR). The resonance from metal nanoparticles has been used in dye-sensitised solar cells to improve their performance. In this work, the dependence of plasmonic properties on the nanoparticle sizes is shown. The gold nanoparticles were prepared using a reduction process where the hydrogen tetrachloroaurate acid was used as the base gold salt and reduced by sodium citrate composed at different molarity ranging from 0.015 to 0.035 mol/L. The method produces monodispersed nanoparticles whose sizes are sensitive to the concentration of chemicals used and the completeness of the reduction process. The process took approximately 18 minutes, and the colour changed from pale yellow to wine red. The absorbance of resulting gold nanoparticles was determined using a UV Vis spectrophotometer within 300 nm to 800 nm. The LSPR peaks were found to occur within 518 nm to 520 nm, and from a Gaussian fit, the FWHM ranged from 45.5 to 51.0 nm. The absorption peaks had a narrow range of 14 nm over sodium citrate's molarity content. A high molarity concentration of 0.035 mol/L produced a small particle with a diameter of 17 nm, while a low concentration of 0.015 mol/L produced a size of 26 nm. The interaction of electrons in the specific orbitals, sp- and d- of nanoparticles exhibited pronounced multiple resonances with a reduction of nanoparticle sizes.