A simplified solid-phase immunofluorescence assay for measurement of serum immunoglobulins

A simple 2-step solid-phase fluoroimmunoassay for the determination of serum immunoglobulins is described. The method employs a stabilized solid-phase immunoadsorbent consisting of antigen immobilized on a cellulose acetate/nitrate disc attached to a plastic StiQTM sampler. The polymeric disc serves both as a substrate for immobilization and as a highly uniform surface upon which very precise fluorescence determinations may be made. The assays rely upon the reaction of a precise and limiting amount of mono-specific fluorescent antibody with the specific antigen present in a test sample. Residual unreacted fluorescently labeled antibody is allowed to bind to the immunoadsorbent; non-specifically bound antibody is removed in a wash step. The amount of labeled antibody bound is inversely proportional to the amount of antigen present in the test sample. The fluorescence of the bound labeled antibody is measured using a FIAX surface-reading fluorometer. Comparison of this new procedure with the commercially available (4-step) FIAX assay, which requires generation of immunoadsorbent in situ, demonstrated excellent correlation between the two methods. The new 2-step procedure provides results in a much shorter period of time and requires one-half to one-eighth of the operator time required for the other available solid-phase fluoroimmunoassays.