Abstract
An immunoassay technique is presented, which works equally well with either a radioactive isotope or an enzyme as the label. It is based on the competition between a labelled antigen of known concentration and an unlabelled antigen (concentration to be determined) for binding to an antibody, which previously has been thiolated by the heterobifunctional reagent N-[3-(2-pyridyldithio)propionyl]succinamide [marketed as N-succinimidyl-3-(2-pyridyldithio)propionate; SPDP)]. The soluble immunocomplex formed is then immobilized onto agarose beads containing reactive disulphide groups. After washing, to remove any unbound and non-specifically adsorbed material, the radioactivity or the enzymic activity on the agarose beads is determined and the concentration of the antigen in the test sample calculated according to the conventional procedure for a competitive immunoassay. In order to demonstrate the applicability of the technique a test procedure for the determination of total serum immunoglobulin E is presented.
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