Use of ISFETs for 24 h pH monitoring in the gastrooesophageal tract

We report the use of ISFETs for monitoring, on a 24 h basis, the pH in the gastrooesophageal tract. The realization of gastric probes with ISFETs presents the advantage of combining the qualities of the glass and antimony electrodes commonly used for gastric pH measurement: stability and small size. Moreover, the very small dimensions of the ISFET chips allow several sensors to be mounted on a single catheter. Such multi-ISFET probes are expected to be very useful in the study of the gastrooesophageal reflux which affects numerous people. The gastric probe is composed of a supple PVC catheter in which the ISFET is mounted on a floppy substrate of kapton. The technique of encapsulation is briefly described. The whole measuring system is composed of the gastric catheter, a small data logger system containing a 10 bit A/D converter with 8 input channels, a microprocessor for data and an expandable 256 kB data storage module, which is carried on the patient's belt for the 24 h period, and a PC for data retrieval and processing. In the present state, the system is operated with two ISFET sensors over 27 h with one pH measurement every 3 s.