Potentiometric Urea Biosensor Based on Carbon Nanotubes and Polyion Complex Film.

Enzymatic electrode for a potentiometric urea sensor was prepared by sequential coating of carbon nanotube (CNT), urease (Urs) and polyion complex (mixture of poly-L-lysine hydrobromide and poly (sodium 4-styrenesulfonate), PIC) on an ITO glass. The prepared electrode (ITO/CNT/Urs/PIC) was characterized by potentiometric measurements at different urea concentrations in Tris-HCI buffer (pH 7.0). The potentiometric response of the electrode was linear in the range of 1 x 10(-5) to 3 x 10(-3) M with a correlation coefficient of 0.999 and a sensitivity of 59.1 mV/decade. It was found that the addition of CNT caused considerable improvement of the sensitivity of the electrode to urea. The response time was approximately 60-90 s. A half of the initial sensitivity was retained for 15-17 d at room temperature.