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We describe a novel separation procedure for immunoradiometric assays involving monoclonal antibodies in which both radiolabeled and capture antibodies are used in solution, the capture antibody being labeled with fluorescein isothiocyanate (FITC). Separation is achieved by incubation with anti-FITC antibodies on magnetic particles. This technique enhances reaction kinetics relative to those of assays in which a solid-phase capture antibody is used, thus allowing faster reaction times and more economic use of the monoclonal antibodies. The use of anti-FITC magnetic solid phase produces an assay having a highly specific separation method, minimal nonspecific binding, and high sensitivity. The method is illustrated by application to assays for thyrotropin and human choriogonadotropin.

We describe an amperometric technique for quantification of an enzyme immunoassay in which we use a magnetic working electrode, both to separate bound and free analyte and to monitor the electrochemical response. We used a "two-site" immunometric assay with monoclonal antibodies for human choriogonadotropin (hCG) as a model system in which magnetic particles were used as the solid phase. Separation of bound and free label is readily achieved by localizing the particles at the electrode. Activity of the bound enzyme in the environment of the electrode is determined electrochemically, permitting rapid quantification of the analyte without the need for a separate incubation step to measure enzyme activity. The sensitivity of the system is 150 int. units of hCG per litre (1st Int. Ref. Preparation). Correlation between the amperometric measurement of urinary hCG and data for an immunoradiometric assay was r = 0.9. The assay is rapid, requiring a total assay time for each sample of 20 min, which includes 15 min for antibody/antigen binding.

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