title: Theoretical limitations on immunoassay sensitivity. Current practice and potential advantages of fluorescent Eu3+ chelates as non-radioisotopic tracers.
abstract: The sensitivity of any immunoassay is a complex function of the underlying physico-chemical basis of the technique and the size and source of 'experimental' errors. Analysis of this relationship emphasizes the distinction between competitive labelled analyte methods, e.g., RIA, and the non-competitive labelled antibody techniques, e.g., IRMA, implying that, in practice, non-competitive methods may display sensitivities which are orders of magnitude greater than similar competitive assays. The achievement of the potential sensitivity of the non-competitive methods depends to a great extent on the application of very highly detectable labels. The long fluorescent lifetime and large Stoke's shift of certain europium (Eu3+) chelates permits such sensitive detection in a commercially available time-resolved fluorimeter. We briefly outline the current application of Eu3+ labels in immunometric assay, compare the application of Eu3+ labels in the immunofluorometric assay of human TSH with conventional RIA and discuss the future potential of this technique.
mesh_terms: D000906:Antibodies; D005063:Europium; D005069:Evaluation Studies as Topic; D005455:Fluorescent Antibody Technique; D007118:Immunoassay; D011863:Radioimmunoassay; D013972:Thyrotropin / Q000032:analysis; D013997:Time Factors
chemical_list: D000906:Antibodies; D005063:Europium; D013972:Thyrotropin