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 photothermal beam deflection quantitation is proposed. Ultrasensitive laser spectrometric analysis of actual biological samples is always obstructed by the background and its fluctuation. However, we could adequately suppress this obstruction by substituting polystyrene microspheres in the antigen-antibody solid-phase reaction instead of the conventional nitrocellulose membrane because the nonspecific adsorption velocity of the admixture proteins was highly restrained and the area of the antigen-antibody reaction was increased. The conditions of the antigen-antibody reaction were optimized using immunoglobulin G (IgG), and the method was shown to be applicable to the determination of trace and weak immunological reactive antigen in a highly dense biological matrix by determining trace IgE in human serum. A significant difference from 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 obtained by EIA and RIA.