Radioimmunoassay

Creative BioMart provides Radioimmunoassay (RIA) that uses antibodies to detect and quantitate the amount of antigen (analyte) in a sample. This assay is typically very sensitive and specific. It is possible to detect as low as a few picograms of analyte in the experimental tube when using antibodies of high affinity (Kd = 10^-8 - 10^-11 M). The basic principle of radioimmunoassay is competitive binding, where a radioactive antigen ("tracer") competes with a non-radioactive antigen for a fixed number of antibody or receptor binding sites. When unlabeled antigen from standards or samples and a fixed amount of tracer (labeled antigen) are allowed to react with a constant and limiting amount of antibody, decreasing amounts of tracer are bound to the antibody as the amount of unlabeled antigen is increased.

125-I labels are usually applied although other isotopes such as C14 and H3 have also been used. Usually, high specific activity radio-labeled (125-I) antigen is prepared by iodination of the pure antigen on its tyrosine residue(s) by chloramine-T or peroxidase methods and then separating the radio-labeled antigen from free-isotope by gel-filtration or HPLC. Other important components of RIA are the specific antibody against the antigen and pure antigen for use as the standard or calibrator.

As an example of how this technique works, let's apply it to insulin. To measure insulin, the first step is to mix known amounts of radioisotope-tagged insulin and antibodies. These combine chemically. Next, a small amount of the patient's blood is added. The insulin contained in the blood displaces some of the tagged insulin. The free-tagged insulin is then measured with isotope detectors and the patient's insulin level is calculated.

RIA has many uses, including narcotics (drug) detection, blood bank screening for the hepatitis (a highly contagious condition) virus, early cancer detection, measurement of growth hormone levels, tracking of the leukemia virus, diagnosis and treatment of peptic ulcers, and research with brain chemicals called neurotransmitters. Creative BioMart has extensive experiences in RIA. For details, please contact us.