Abstract
A flow-through cell module, containing embedded FET-based chemical sensors, was built and its performance was characterized in terms of pH-sensitivity. An indium tin oxide coated polyethylene-terephthalate (ITO/PET) foil with a high surface resistivity (300 Ω/sq), as the ion-sensitive layer, was connected to the gate terminal of a MOSFET. The result is an inexpensive extended-gate field-effect transistor (EGFET) sensor suitable for pH-sensing. The flexible ITO/PET foil was lasermicromachined and encapsulated using a Plexiglas cap and a double-sided adhesive, presenting a simple, low-volume (6 µl), and low-cost package. The dual cell configuration of the sensor makes differential sensing possible and thus eliminates the role of bulky glass reference electrode inside the measurement cell. Corrosion of the ITO/PET electrode in the acidic, neutral, and basic aqueous solutions was studied by electrochemical impedance spectroscopy (EIS) technique. EIS result is compared with the one gained using an ITO/PET with a low surface resistivity (8 - 10 Ω/sq) to compare for the redox reaction rate. The sensor showed pH-sensitivities in the range of 50 - 55 mV/pH within the pH-ranges of 3 to 12.
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