Reference-Electrode Free pH Sensing Using Impedance Spectroscopy

• Main Authors: Laura Folkertsma, Lennart Gehrenkemper, Jan Eijkel, Karin Gerritsen, Mathieu Odijk
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Proceedings
• Subjects: pH sensor; impedance spectroscopy; conductivity; indium tin oxide; double layer capacitance; human plasma
• Online Access: https://www.mdpi.com/2504-3900/2/13/742

We present a reference-electrode free sensor able to measure both pH and conductivity<br />based on impedance spectroscopy. The electrode is made of a layer of indium-tin-oxide (ITO). The<br />impedance of this electrode at low frequencies depends on its double layer capacity, which varies<br />with pH due to modification of oxide groups at the ITO surface. At high frequencies, the impedance<br />is determined by the resistance in the system, which corresponds to the inverse conductivity of the<br />solution. Because no reference electrode is needed for this technique, miniaturization of the pH<br />sensor is simple. We demonstrate a proof-of-principle experiment of the sensor for human plasma<br />pH measurements.