PCB-based Mass-produced EGFET pH Sensor with Electroplated Reference Electrode for Daily Saliva Acidity Monitoring in Mouth

A high performance pH sensor chip with integrated reference electrode on a mass-producible printed circuit board (PCB) is developed for directly measuring saliva pH level in mouth. Commercially available indium-tin-oxide (ITO) thin film and the on-PCB electroplated Ag/AgCl reference electrode are utilized for detecting the hydrogen ions under an extended gate field effect transistor scheme. To produce flat AgCl on the reference electrode surface, silver plating is performed using homemade silver electroplating solution, followed by chemical chlorination using FeCl3. The integrated sensor chip exhibit excellent sensitivity (84.6 mV/pH), good linearity (R2=0.9999), and rapid response time (< 2 s) for pH measurement. It facilitates easy monitoring of saliva pH before and after meals, supporting daily oral health care.