Prevention of bridge binding effects in haptenic immunoassay systems exemplified by an iodinated radioimmunoassay for melatonin.

Antisera used in immunological assay systems for small molecular weight substances are routinely prepared by coupling the hapten to a carrier protein via a chemical linker. Often this bridge is partly recognized by the antibody, resulting in reduced sensitivity when an identically structured tracer (e.g. iodine-labelled) is used. Historically, the problem was solved by changing the linking structures in the tracer. An alternative way is exemplified by the development of a very sensitive and specific iodinated radioimmunoassay for melatonin. This new approach involves the design of a linkage identical in the tracer and the antigen that is both very short and closely resembling the structure of the analyte itself.