An overview of various labeled assays used in medical laboratory diagnosis. Immune and non-immune assays.

In this review, some light is thrown on various labeled immunoassays that depend on antigen-antibody (Ag-Ab) reactions, including immunofluorescence, radioimmunoassay, and enzyme immunoassay (EIA or ELISA). Their definitions, principles, and applications are described, then they are discussed chronologically to show their stepwise development that led finally to full automation. Enzyme labeled immunoblot assays (Western blot, blot spot, and recombinant immunoblot assay), and luminescence (bioluminescence and chemiluminescence) are also discussed chronologically. Labeled assays, that do not involve Ag-Ab reaction but rather, utilizing biotin-streptavidin (BS) interaction and probe-target DNA interaction, are described, together with their applications for DNA/RNA detection and genotyping. Finally, included in the discussion were some luminescent labeled techniques that utilize the immune Ag-Ab reaction together with non-immune BS reaction, such as the luminescent oxygen channeling immunoassay, and its commercialized AlphaLISA, both eliminate the washing steps without sacrificing high sensitivity, or wide dynamic range.