In this paper, we describe the development of a solid-type pH sensor with an ultra-low power consumption of 8.2× 10-4 mAh per measurement and a reasonably high accuracy of 0.1 pH for the real-time monitoring of the rumen of a cow. The sensor combines a metal-oxide-semiconductor field-effect transistor with a separate gate as the sensing electrode, and was fabricated using indium tin oxide with an optimized capture structure that incorporates protective micro-fabricated dots. The evaluation results show that the sensor has high-sensitivity of > 14 μA/pH, and maintains a stable baseline at pH 7 over the course of several days in the rumen. We performed a comprehensive calibration of the solid pH sensor, and carried out a field test, which clearly demonstrated that the pH values are strongly dependent on the activities of the cow, as recorded by a camera. The developed pH sensor is believed to be of significance for preventing disease, as well as for improving the efficiency of food production.
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