Reference-Electrode Free pH Sensing Using Impedance Spectroscopy
Laura Folkertsma,
Lennart Gehrenkemper,
Jan Eijkel,
Karin Gerritsen,
Mathieu Odijk
Affiliations
Laura Folkertsma
BIOS-Lab on a Chip Group, MESA+ Institute of Nanotechnology, Technical Medical Centre, Max Planck Center for Complex Fluid Dynamics, University of Twente, 7500 AE Enschede, The Netherlands
Lennart Gehrenkemper
BIOS-Lab on a Chip Group, MESA+ Institute of Nanotechnology, Technical Medical Centre, Max Planck Center for Complex Fluid Dynamics, University of Twente, 7500 AE Enschede, The Netherlands
Jan Eijkel
BIOS-Lab on a Chip Group, MESA+ Institute of Nanotechnology, Technical Medical Centre, Max Planck Center for Complex Fluid Dynamics, University of Twente, 7500 AE Enschede, The Netherlands
Karin Gerritsen
Department of Nephrology and Hypertension, University Medical Center Utrecht, 3508 GA Utrecht, The Netherlands
Mathieu Odijk
BIOS-Lab on a Chip Group, MESA+ Institute of Nanotechnology, Technical Medical Centre, Max Planck Center for Complex Fluid Dynamics, University of Twente, 7500 AE Enschede, The Netherlands
We present a reference-electrode free sensor able to measure both pH and conductivitybased on impedance spectroscopy. The electrode is made of a layer of indium-tin-oxide (ITO). Theimpedance of this electrode at low frequencies depends on its double layer capacity, which varieswith pH due to modification of oxide groups at the ITO surface. At high frequencies, the impedanceis determined by the resistance in the system, which corresponds to the inverse conductivity of thesolution. Because no reference electrode is needed for this technique, miniaturization of the pHsensor is simple. We demonstrate a proof-of-principle experiment of the sensor for human plasmapH measurements.
