  The dependence of the surface plasmons resonance (SPR) frequency on the size
of gold nanoparticles (GNPs) is experimentally studied. The measured data for
the SPR frequency by UV-Vis spectroscopy and GNPs diameter by Dynamic Light
Scattering (DLS), Transmission Electron Microscopy (TEM) and Atomic Force
Microscopy (AFM) are collected in the course of classical citrate GNPs
synthesis. The relationship between the GNPs size and the blue shift of the
light absorption is presented. They are fitted by an equation with a single
free parameter, the dielectric permittivity of the surrounding media. Thus, the
refractive index of the surrounding media is determined, which characterizes
the GNPs surface shell.
