A urea sensor based on an ammonium-ion-sensitive field-effect transistor has been realized in combination with an immobilized urease membrane. The effect of buffer concentrations on the response characteristics of the sensor is investigated. The lower detection limit, as given by the calibration curve, is strongly affected by the concentrations of potassium and sodium ions, while its slope in the appropriate buffer solution is independent of the buffer concentration in a limited urea concentration range. Although the slope in physiological saline solution is only 18 mV/dec, the dynamic range of the sensor covers the physiological range of urea in blood. The small slope and the narrow dynamic range are found to be due to poor selectivity of the ammonium-ion-selective membrane over sodium and potassium ions. It is, therefore, possible to improve the sensor response characteristics by improving the selectivity of the ammonium-ion-selective membrane.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Metals and Alloys
- Electrical and Electronic Engineering
- Materials Chemistry