Optical properties of colloidal gold and its conjugates with biospecific macromolecules

This work is devoted to methods of optical control for the preparation of gold sols and their conjugates with biospecific macromolecules. Attenuation spectra for polydisperse (by the dimensions and shapes of the particles) sols were calculated using the Mie theory, T-matrix method, and sets of various experimental optical constants of bulk gold, modified taking into account dimensional effects. The most general model involving polydispersity of the dimensions and shapes and dimensional dependence of the imaginary part of permittivity was shown to adequately fit the experimental measurements of the dependence of the position and the maximum of attenuation on the dimensions of the particles. Attenuation spectra of sols in were calculated for various models the range 350 - 800 nm and were compared with the experimental spectra of synthesized sols with average dimensions of the particles equal to 5, 10, 24, and 40 nm. Calibration curves for on-line spectrophotometric control of the dimensions of gold particles and of the amount of reducing agent required to prepare particles with specified dimensions were obtained using electron-microscopic and spectral data. Data on stabilizing concentrations and attenuation spectra for conjugates of colloidal gold with ovomucoid are presented. It was shown that the simplest two-layer spherical model of a conjugate can provide an adequate explanation of the basic changes in the spectra of the sols after conjugation with specific biomacromolecules, allowing some conclusions on the structure of the adsorbed layer to be drawn.