Imaging immunoassay in negative: surface-catalysed chemiluminescence for the detection of pregnancy hormones in artificial saliva†
A novel and rapid (45 min), quantitative chemiluminescence-based, surface immunoassay is reported for the detection of progesterone and œstriol in artificial saliva. The detection limits for these pregnancy hormones are 2.3 and 2.5 pg mL−1, respectively. The assay is based on the use of ferrocene-tagged, monoclonal antibodies immobilised on a surface, so that the oxidised ferricenium catalyses the reaction between luminol and hydrogen peroxide. The immunoassay is performed in negative, such that increasing the antigen concentration gives rise to decreasing light intensity that is observed, and is unaffected by antibody orientation on the surface. This affords a method of calibration that is readily translated to pregnancy hormone detection in a primary point-of-care environment. Biomolecules with similar structures to these pregnancy hormones found in saliva are demonstrated not to interfere with the immunoassay.