ULTRASENSITIVE HETEROGENEOUS IMMUNOASSAY USING PHOTOTHERMAL DEFLECTION SPECTROSCOPY

A novel ultrasensitive, highly selective immunoassay method that uses gold ultrafine particles as the labeling material and laser-induced ph otothermal beam deflection quantitation is proposed. Ultrasensitive la ser spectrometric analysis of actual biological samples is always obst ructed by the background and its fluctuation. However, we could adequa tely suppress this obstruction by substituting polystyrene microsphere s in the antigen-antibody solid-phase reaction instead of the conventi onal nitrocellulose membrane because the nonspecific adsorption veloci ty of the admixture proteins was highly restrained and the area of the antigen-antibody reaction was increased. The conditions of the antige n-antibody reaction were optimized using immunoglobulin G (IgG), and t he method was shown to be applicable to the determination of trace and weak immunological reactive antigen in a highly dense biological matr ix by determining trace IgE in human serum. A significant difference f rom the background was obtained for 8.4 x 10(-3) IU/mL using a 50-muL sample, corresponding to the absolute quantity of 2.0 pg (10.7 amol), a result that was at least 1 order of magnitude superior to results ob tained by EIA and RIA.