​Effective reproduction management is one of the keys to profitable cattle farming. But it isn't always easy to time insemination. Farmers use visual observation to determine when the cows are about to ovulate. Changes in behavior, such as standing to be mounted, only last a few hours, however, and farmers have to keep an eye on entire herds. The tools currently available include behavior detection sensors and sensors that detect hormone fluctuations in the cows' milk.

A PhD research project co-financed by CEA-Leti, the Auvergne Rhône Alpes regional government, and INRAe as part of the EU SmartRepro project, resulted in a new solution: a painless ear patch worn throughout the cycle. The patch is made of 3D-printed hollow polymer microneedles that penetrate the skin of the cow's ear to a few hundred microns. The needles collect a mixture of blood and interstitial fluid, which then travels through a microfluidic circuit to a chamber containing SGFET biosensors that can detect the presence of certain hormones in real time.

Made of a transistor and graphene gate, these SGFET sensors are widely used in biology because they are so sensitive. In the patch, hormones are trapped by hybridization with aptamers (small strands of DNA) attached to the graphene. The biosensor measures the change in charge distribution at the the fluid/graphene interface to detect ovulation 24 to 48 hours before it occurs. Ultimately the electronics that transmit the results will also be integrated into the patch for real-time monitoring, and the aptamers will be optimized for better target recognition.