Solid-State Sensor Chip Produced with Single Laser Engraving for Urine Acidity and Total Dissolved Ion Detections

Abstract

This paper presents a solid-state sensor for rapidly detecting the acidity and the total dissolved ions of urine. The sensor is produced by direct laser engraving the commercial touch panel film to pattern the sensing areas. Since the indium tin oxide on the touch panel film is an n-type degenerate semiconductor, hydrogen ions in the solution spontaneously attach onto the ITO surface and change the zeta potential of it. The sensing area is connected to the gate of a commercial N-MOSFET CD4007 to establish the extended-gate FET sensing scheme. Full ITO-based sensing chips for pH and total dissolved ions in urine can be easily produced in the developed rapid manufacturing process. Home-build circuits embedded in hand-held devices are produced for the measurement. Results show that the developed ITO-based sensor exhibits high sensing performance for acidity measurement of 0.11 V pH−1 with rapid responses of less than 1 s and low temperature drifting of 0.0205 pH °C−1. The sensor can also detect total dissolved ions with a concentration of 0.1−30 mS in urine. The performance of the developed sensor is characterized by a classic physiology experiment of kidney elution after taking various liquids of reverse osmosis water, beer, and normal saline.