New optical method for determination of antigen-antibody reaction using level-crossing technique

Presented here is a new method of optically detecting agglutination reactions through counting the number of level-crossings of light intensity fluctuations scattered by coated carrier particles. The theory behind this technique is that the number of level-crossings decreases as the size of aggregated particles and, accordingly, the antigen concentration increases. The antigen used in this experiment is immunoglobulin E (IgE). The crossing level is fixed at the average intensity of the scattered light. The detectable range is from 17 to 1000 IU/ml under this condition. The incubation time is 15 min. The coefficient of variations (CVs) of the number of level-crossings is reasonably low, between 0.382 and 3.05% (n = 5). Through simple data processing involving comparison of the data with the crossing level and counting the number of level-crossings, it is possible to determine the antigen concentration on a real time basis.