The Avidin-Biotin complex in solid phase radioimmunoassays

A solid-phase radioimmunoassay is described in which biotin conjugated antibodies are used to replace¹²⁵I labeled antibodies to individual antigens. The amount of antigen present is subsequently determined by the binding of¹²⁵I-labeled avidin. This method is appealing for a variety of reasons. (a) Only one¹²⁵I-labeled protein (avidin) need be prepared and characterized for all affinity systems, (b) There is no need to purify individual antibodies. (c) Biotin can be attached to antibodies under mild conditions. (d) The size, physical characteristics, and biological activity of the biotin-derived antibody are only nominally affected. (e) The biotin-avidin complex is of exceptionally high affinity and stability, (f) Introduction of biotin groups into the antibodies leads to amplified radioactive tracer binding, (g) Avidin and biotin are commercially available.