  The use of a scanning flow cytometer (SFC) to study the evolution of
monomers, dimers and higher multimers of latex particles at the initial stage
of the immunoagglutination is described. The SFC can measure the
light-scattering pattern (indicatrix) of an individual particle over an angular
range of 10-60 deg. A comparison of the experimentally measured and
theoretically calculated indicatrices allows one to discriminate different
types of latex particles (i.e. monomers, dimers, etc.) and, therefore, to study
the evolution of immunoagglutination process. Validity of the approach was
verified by simultaneous measurements of light-scattering patterns and
fluorescence from individual polymer particles. Immunoagglutination was
initiated by mixing bovine serum albumin (BSA)-covered latex particles (of 1.8
um in diameter) with anti-BSA IgG. The analysis of experimental data was
performed on the basis of a mathematical model of diffusion-limited
immunoagglutination aggregation with a steric factor. The steric factor was
determined by the size and the number of binding sites on the surface of a
latex particle. The obtained data are in good agreement with the proposed
mathematical modeling.
