Radioimmunoassay

Part of speech: noun

Definitions

1. A specialized laboratory procedure used to measure specific antigens by utilizing antibodies labeled with radioactive isotopes
2. This method allows for the detection and quantification of molecules in samples through the binding of radioactively tagged antibodies to their targets
3. A laboratory method that uses radioactive markers attached to antibodies to detect and quantify specific molecules in a sample

Etymology: Radioimmunoassay is a compound built from "radio-" and "immunoassay," and its story is really the story of its two halves. The "radio-" element comes from Latin "radius," meaning a ray or spoke of a wheel, which was later applied to radiation and radioactivity. The "immuno-" element traces back to Latin "immūnis," meaning exempt from public service or duties, from "in-" (not) and "mūnus" (duty, service). Medieval Latin and Middle French carried that sense of exemption into medical use, so an immune person was one exempt from disease, and "immune" entered English in the Middle English period. "Assay" is a separate story: it comes from the idea of testing or weighing a substance to determine its content, and "immunoassay" applied that testing principle to antibodies. Putting "radio-" in front marks the method's key trick, which is tagging the antibody with a radioactive label so that even tiny amounts of a target molecule can be measured by the radiation the label gives off.