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Background
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Solid phase immunoassay utilizing microtiter plates are the predominant assay format for the detection of low concentration small molecules in biological samples. The primary antibody to these small molecules serves two purposes, it confers specificity for the assay by selectively binding the small molecule, and, in binding it deter- mines the sensitivity of the assay. Small molecule assays require a competitive immunoassay technique where the small molecule antigen binds to a limiting amount of the primary antibody in competition with a labeled re- porter small molecule, such as HRP. Primary antibodies can be coated on solid phases but the technique is difficult to reproducibly accomplish, as the dilution of the primary antibody has to be tightly controlled across all of the coated plates and the amounts of primary antibody required can be high. Secondary generic coated plates using donkey anti-sheep IgG antibody coating can be carried out easily and after being blocked and dried these plates are stable for many years. Typical primary antibody titers using coated generic plates can be 10 fold lower than directly coated primary antibodies.
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