Light scattering from dimers: latex-latex and gold-latex

Abstract

This paper presents theoretical modeling and experimental results of light scattering studies on latex (polystyrene) particle dimers and colloidal gold particles coupled to individual latex particles. The latex particle size range is 1 - 10 micrometer (in diameter) and that of the gold particles is 80 - 100 nm. In general, the latex particles are spherical, while the colloidal gold particles have varied shapes. The theoretical model is based on exact solution of the problem of light scattering by interacting spheres. Calculations based on interacting and noninteracting particles will be compared to experimental results. The experimental results were obtained with high resolution light scattering measurements of particle coupling in a flow particle analyzer. This analyzer, Copalis<SUP>TM</SUP> (Coupled Particle Light Scattering), exploits particle coupling induced by antigen-antibody, receptor- hormone, or nucleic acid interactions in medical diagnostic assays. Although latex particle coupling produces a range of aggregate sips, only dimer light scattering results are relevant. Coupling of gold to latex particles in the Copalis<SUP>TM</SUP> diagnostic system produces from one to many gold particles per latex particle. Coherent addition of fields scattered by many gold-latex pairs has been used to simulate the gold-based assay. The comparison of theoretical simulations and experimental results for the coupling will be discussed. The results of this study are being used to refine the particle coupling results in the Copalis<SUP>TM</SUP> diagnostic system.