by Radioimmunoassay
Radioimmunoassay (RIA) is an immunological assay technique used for detecting and quantifying substances in a biological sample. It is a very sensitive laboratory technique using the principles of competitive binding between labeled and unlabeled antigen or ligand and antibody. In a RIA, an unknown amount of antigen or hormone in a biological sample such as serum competes with a known amount of labeled antigen for binding sites on specific antibodies. The bound and free fractions of the labeled antigen can then be separated, and the amount of labeled antigen bound to the antibody is measured. This provides a quantitative measurement of the original antigen or hormone concentration in the sample.
History and Development of RIA
The development of RIA in the 1950s enabled the accurate measurement of minute quantities of biological substances
Radioimmunoassay for the first time. Hungarian-born physician Solomon Berson and American physiologist Rosalyn Yalow were pioneering scientists who worked on the development of RIA in the late 1950s. Their work led to the development of techniques for measuring insulin in the blood, which earned them the 1977 Nobel Prize in Physiology or Medicine. This technique allowed clinicians to accurately monitor insulin levels in diabetic patients and understand the relationship between insulin, blood glucose, and diabetes in more detail.
The key innovation by Berson and Yalow was the use of radioactive labeling of a known quantity of antigen or hormone and then using the labeled antigen in a competitive binding assay against the unknown quantity in a biological sample. Other researchers soon adopted the technique, leading to the accurate quantification of many other important hormones and biological substances in minuscule amounts. RIA revolutionized the fields of endocrinology, pharmacology, and clinical chemistry and allowed earlier diagnosis and treatment monitoring of various disorders.
How Does Radioimmunoassay Work?
In a RIA, a known quantity of antigen is radiolabeled, usually with radioactive isotopes like iodine-125 or tritium. This labeled antigen and a biological sample containing an unknown amount of the same antigen are then mixed with a fixed quantity of specific antibodies against that antigen. Both the labeled and unlabeled antigens, i.e., the sample antigen, compete with each other for the binding sites on the antibody molecules. The labeled and unlabeled antigen-antibody complexes are then separated from the unbound labeled antigen using techniques like magnetic separation or centrifugation. The fraction of labeled antigen bound to the antibody is then quantified using a gamma counter or liquid scintillation spectrometry.
By comparing the levels of bound and unbound radioactive labels, the concentration of the unlabeled antigen in the original sample can be derived after plotting a standard calibration curve. This ability to quantify minute quantities of a substance using radioisotopes and competitive binding principles made RIA a highly sensitive technique for measuring bioactive substances like hormones, drugs, metabolites, etc. present in biological fluids in picomolar or even femtomolar concentrations, far below the limits of detection of other techniques available at that time.
Applications and Advantages of Radioimmunoassay
Some key applications and advantages of RIA include:
– Measurement of peptide and protein hormones like insulin, thyroid hormones (T3, T4), cortisol, prolactin, human growth hormone, etc. in clinical chemistry, endocrinology, and diabetes management.
– Monitoring therapeutic drug and metabolite levels in pharmacokinetic studies and ensuring patient compliance in chronic medication therapies.
– Diagnosis of endocrine and metabolic disorders by hormonal assays.
– Prenatal screening and testing for genetic disorders like Down’s syndrome.
– Environmental monitoring of pollutants, pesticides, and other chemicals in trace amounts.
– Sensitive detection of diseases through tumor marker assays and viral load monitoring in HIV infection.
– High precision and accuracy even at very low analyte concentrations in the picomolar/femtomolar range.
– Capability to multiplex by performing assays for multiple analytes on the same patient sample.
– Relatively simple protocol and does not require expensive analytical instruments.
Impact and Later Developments
Radioimmunoassay revolutionized clinical biochemistry and enabled an explosion of knowledge about various physiological and pathological hormone systems. It had tremendous utility in endocrine disorders, diabetes research, prenatal screening, toxicity monitoring, and receptor biology. The technique was also quickly adopted in other areas like pharmacology and environmental sciences. Recombinant DNA technology later facilitated generating monoclonal antibodies, leading to enhanced assay sensitivity and specificity. Automated formats and non-radioactive alternative methods have also been developed to reduce health hazards from radioisotope use. Despite competition from other techniques, the RIA principles still remain valuable in analytical biochemistry and biotechnology after over 60 years due to unmatched sensitivity and multiplexing ability.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
