Rapid flow-through enzyme immunoassay of progesterone in whole cows' milk.

A rapid flow-through immunoassay using an enzyme (horseradish peroxidase) as a label for quantitative and semi-quantitative determination of progesterone in whole cows' milk was developed. The flow-through test device consisted of a porous nitrocellulose membrane coated with antibodies and an absorbent membrane. The substrate solution containing 3,3',5,5' -tetramethylbenzidine was used for colour visualization. The detection limit of 0.4 ng/mL P4 was obtained by this method; analysis time did not exceed 15 min. To eliminate matrix interference a simple sample preparation procedure was used. Results of analysis of whole cows' milk samples with flow-through method were in good correlation with ELISA results (R = 0.96, n = 34). The developed rapid flow-through test system showed high efficiency for the determination of progesterone level in whole cow's milk and can be used on-site for quick identification of milk samples with low and high progesterone concentration.