Free Prostate Specific Antigen (fPSA) ELISA

The principle of the following enzyme immunoassay test follows a typical one-step capture or ‘sandwich’ type assay. The assay makes use of two highly specific monoclonal antibodies: A monoclonal antibody specific for fPSA is immobilized onto the microplate and another monoclonal antibody specific for a different region of fPSA is conjugated to horseradish peroxidase (HRP). fPSA from the sample and standards are allowed to bind simultaneously to the plate and to the HRP conjugate. The washing and decanting steps remove any unbound HRP conjugate. After the washing step, the enzyme substrate is added. The enzymatic reaction is terminated by addition of the stop solution. The absorbance is measured on a microtiter plate reader. The intensity of the color formed by the enzymatic reaction is directly proportional to the concentration of fPSA in the sample. A set of standards is used to plot a standard curve from which the amount of fPSA in samples and controls can be directly read.