A competitive immunoassay enables detection of an antigen (target) with use of a single capture antibody attached to the surface of a microsphere and a competitive, labeled antigen reversibly bound to the antibody. An analyte of interest in the sample competes with the labeled antigen causing a decrease in detected signal. A reverse version of the assay is also possible in which the analyte in the sample competes away the labeled antibody in solution rather than on the surface of the microsphere. A version of competitive assays on xMAP® Technology was used extensively in the development of the Gardasil® vaccine.
GARDASIL® is a registered trademark of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Whitehouse Station, NJ, U.S.A.