A luminescent label for the immunoassay of oxytocin

Chemiluminescent labels have been shown to be interesting alternatives to radioisotope labels. Disadvantages of the latter are preparation of e.g. labelled protein/peptides every four to six weeks, and problems with storage and disposal. Amino-Butyl-Ethyl-Isoluminol(ABEI) was attached to the alpha-amino function of the N-terminal amino acid residue of oxytocin; this complex was used in immunoassays for oxytocin. This non-isotopic label did not require heating at 60 degrees C for optimal light-signal development, a procedure usually required for chemiluminescent labels. Standard curves were set up employing the ABEI-label on the one hand and 125I-label on the other. Under identical conditions of final antibody concentration and amount of label, a comparison was made between the performance of the luminescent immunoassay (LIA) and that of the radioimmunoassay (RIA). We conclude that the LIA systems resulted in standard curves of high precision; in comparison with RIA, the sensitivity of the LIA curves is not yet sufficient for the determination of oxytocin concentrations in e.g. human biological fluids. Further improvements in sensitivity of the LIA systems are to be expected by selection of other luminescent labels or by the use of a more sensitive measuring device.