Abstract: This invention provides a means for determining the concentration of any of a wide range of antibody or antigen molecules with a high degree of specificity, accuracy and sensitivity. Antigen or antibody concentration is determined by effecting an agglutination reaction in a liquid medium and determining the cluster size distribution of agglutinated particles by optical pulse particle size analysis. The measured cluster size distribution then is compared with a standard quantitative relationship between the cluster size distribution and concentration of the antigen or antibody being tested. By this means one may specifically ascertain the absolute concentration of the antigen or antibody in question in the sample being analyzed. In addition to detecting antigen or antibody molecules, the process of this invention can be used to determine the concentration of any substance capable of specifically promoting or inhibiting an agglutination reaction such as viruses, white blood cells or the like.

Abstract: A system for determining the cluster size distribution of submicron-size particles in a solution by optical pulse particle size analysis is provided. The system comprises a laminar flow cell having a translucent chamber, means for passing a sheath liquid and a sample liquid through the chamber, a light source and means for focusing the beam of light onto the chamber of the flow cell, a collecting lens, means for limiting collected light to a low angle, a stop, an iris, a light sensor and a means for processing the light signals. The system employs a combination of improved features which allows ultra-sensitive measurement of the cluster size distribution of particles, and can reliably detect as few as three dimers for every 10,000 monomers of micron size particles.