In a typical competitive binding assay, a known quantity of a labeled molecule (often a radiolabeled or fluorescently labeled toxin) is mixed with the sample containing the unknown concentration of the same or similar unlabeled molecule. Both the labeled and unlabeled molecules compete for binding to a specific receptor or antibody. The amount of labeled molecule that binds to the receptor is inversely proportional to the concentration of the unlabeled molecule in the sample. This relationship allows for the quantification of the target molecule.
