Immunochromatographic assay for quantitation of milk progesterone

We describe a rapid immunochromatographic method for the quantitation of progesterone in bovine milk. The method is based on a 'competitive' assay format using the monoclonal antibody to progesterone and a progesterone-protein conjugate labelled with colloidal gold particles. The monoclonal antibody to progesterone is immobilized as a narrow detection zone on a porous membrane. The sample is mixed with colloidal gold particles coated with progesterone-protein conjugate, and the mixture is allowed to migrate past the detection zone. Migration is facilitated by capillary forces. The amount of labelled progesterone-protein conjugate bound to the detection zone, as detected by photometric scanning, is inversely proportional to the amount of progesterone present in the sample. Analysis is complete in less than 10 min. The method has a practical detection limit of 5 ng of progesterone per ml of bovine milk.