Ultra-Long-Life Miniature pH Sensor with a SMA Valve-Actuator Integrated Liquid Junction for Rumen Monitoring

We successfully demonstrated an ultra-long-life miniature pH sensor that employed a newly-developed Ag/AgCl reference electrode (RE) with a valve-actuator-integrated liquid junction. Because previous studies reported that the short life span of REs is caused by an outflow of internal electrolyte, we introduced a valve actuator to reduce the outflow. The results of our study indicated that potential was measured for 24 h with a 0.47-mV drift and the life was estimated to be 2.3 years, which is significantly longer than that of conventional REs. By applying this technique to a miniature pH sensor, the innovative performance, in terms of accuracy (pH error ≤0.1) and life expectancy (more than two years), could be estimated.