In a non competitive test, a specific antibody/antigen is attached on the support and the sample containing antigen/antibody is added. If antigen recognize antibody, a specific antigen-antibody reaction occurs. After this step, a second antibody/antigen marked by a label is added.
If the label is a chemical molecule, the detection technology is a Chemiluminescent immunoassay CLIA.
If the label is a fluorescent molecule, the detection technology is a Fluorescent immunoassay FLIA.
If the label is a radioactive molecule, the detection technology is a Radio immunoassay RIA. This isotope is a moderately high-energy y—emitter with a half-life of 60 days. While its sensitivity of detection is excellent, approximately 5 x 10-18 mol being the practical limit damage caused by its incorporation into protein results in a restricted shelf-life and frequently compromised immunological performance.
Choice of format depends on intended application of the assay, types of sample to be analyzed and availability of reagents.
The reaction ensuing is bringing to light by a changing colour product or fluorescence. The signal is proportional of the antigen/antibody concentration and measured by a spectrophotometer.