A small pH sensor catheter of the endoscope for acidity test of gullet and stomach

The detection of pH in the gullet and stomach is highly significant for the diagnosis of gastroesophageal reflux disease (GERD), particularly with the use of a pH sensor in vivo. Most conventional pH sensors are used singly and could not be inserted in the endoscope's working channel. Because the ion sensitivity field-effect transistor (ISFET) chip has become very small, we have made the pH sensor smaller than a conventional glass pH sensor, and have used it. In this paper, we introduce a small in vivo pH sensor catheter of 2.7 mm diameter and 8 mm length, which can be put in the endoscopy's working channel of 3 mm diameter. The catheter was evaluated in buffer solution (pH 2-12) and its sensitivity was 43 mV/pH. It was confirmed that the catheter properly functioned during an animal experiment.