Improved Biosensor for Measurement of Progesterone in Bovine Milk

A biosensor for online measurement of progesterone was designed and calibrated. The objectives were to developan improved immunoassay sensitive enough to measure progesterone in milk at follicular phase concentrations in realtime,and to design a biosensor for implementation of the detection chemistry. Antiprogesterone antibody was coated on smalldisks of nitrocellulose membrane, which were inserted in the reaction chamber prior to testing. An antigen capture formatwas used with 5 minutes for binding and peroxidaselabeled progesterone as the competitor, and 3 minutes for substratedevelopment with tetramethylbenzidine as the chromophore. The sensor was designed using micropumps and valves undercomputer control, and tested fluid volumes of about 1 ml. Output was read as the rate of change in optical density at 645 nm.An automated sampler was designed to draw a test volume at the start of milking from the long milk tube using a 4way pinchvalve. The system could execute a measurement cycle in about 10 min, and progesterone could be measured at concentrationslow enough to distinguish midluteal phase cows (210 ng/ml) from follicular phase cows (<1 ng/ml). The 95% confidenceinterval for a 0.5 ng/ml reading was estimated to be 0.2 to 1.5 ng/ml.