Bioelectrochemical immunoassay for human chorionic gonadotrophin in serum using an electrode-immobilised capture...

An amperometric technique for the quantification of an enzyme immunoassay which utilises a capture antibody covalently attached to a carbon electrode is described. The electrode is used both to separate the assay and to monitor the activity of the bound enzyme label. A 'two-site' immunometric assay with monoclonal antibodies directed against human chorionic gonadotrophin (HCG) was used as the model system. The activity of the enzyme bound to the electrode is determined electrochemically by the use of an electron transfer mediator (dimethylaminomethyl ferrocene) permitting rapid quantification of the analyte without the need for a separate incubation step to measure enzyme activity. The sensitivity of the assay is 9mIU HCG ml-1 in serum (1st International Reference Preparation). The correlation between the amperometric measurement of serum HCG and data for an immunoradiometric assay was r = 0.988. The assay is rapid requiring a total assay time of 20 min per sample, which includes 15 min for antibody-antigen binding.