Absorption spectra from colloids containing different concentrations of spherical gold nanoparticles in water were measured with a spectrophotometer. The absorption spectra were used to calculate the number density of nanoparticles (NPs) with the aid of an unconventional finite spectral band <i>f</i>-sum rule applied for gold colloid. Good correlation between the number density of dispersion electrons, obtained from the <i>f</i>-sum rule, and the number density of nanoparticles was found. The effective absolute refractive index of the gold colloid was obtained with the aid of a singly subtractive Kramers–Kronig relation, and in addition the refractive index change due to the nanoparticles was obtained with the aid of a conventional Kramers–Kronig relation. Such optical properties are valuable in studies of light interaction with nanoparticles.
Vol. 6, Iss. 8 Virtual Journal for Biomedical Optics
Ville Kontturi, Pertti Silfsten, and Kai-Erik Peiponen, "Finite Frequency f-sum Rule for Assessment of Number Density of Gold Nanoparticles (AuNPs) and Kramers–Kronig Relation for Refractive Index of Colloidal Gold," Appl. Spectrosc. 65, 746-749 (2011)