Dielectric Function of Gold Nanoparticles Synthesized Using Camellia sinensis Extract

The goal of this study is to show how to synthesize gold nanoparticles, and present a method to determine the dielectric function of nanoparticle dispersions that are used in optical biosensing applications. Camellia sinensis (green tea) leaf extract was used as a reducing agent to obtain nanoparticles. The gold nanoparticles were synthesized using different concentrations of green tea, which directly impact the particle size and refractive index. The experimental data from the absorption spectroscopy of colloidal solutions and the zeta potential measurements were used to determine the dielectric parameters of the gold nanoparticles. Three theoretical expressions proposed for the dielectric function have been used to estimate the measured absorption coefficient whose curves have a behavior that is quite similar to the ones obtained by UV-Vis spectrophotometry. The absolute error of the peak value of the absorption coefficient is less than 1.5% in the case of the theoretical expression that most accurately describes the dielectric function of the colloidal solution of gold nanoparticles.