Abstract
A new method is presented here for detection of immunoreactions based on the measurement of intensity fluctuations of the depolarized light which is scattered in the forward direction by coated spheres.
Although the single scattered light by microspheres is polarized parallel to the incident light polarization, the double scattered light contains depolarized components. The normalized fractional variance from the double scattered field is inversely proportional to the square of the particle concentration, whereas that of the single scattered field is inversely proportional to the concentration. Therefore, the decrease of the concentration is sensitively detected by the measurement of the normalized fractional variance of the depolarized scattered light. In addition, undesirable single scattered light from microspheres is reduced by the present method.
The carrier particles used were latex spheres with diameter of 0.2μm. Latex spheres coated with antibody molecules aggregated after the addition of the antigen. The measured concentration of latex spheres was 4.5×1011 particles/cm3, which was most convenient for obtaining double-scattered light. In these conditions, the fractional variance rapidly increased thereafter, and leveled off after 5-10 minutes. The antigen measured was α-fetoprotein (AFP) and immunoglobulin E (IgE).
