All-solid-state paper based potentiometric potassium sensors containing cobalt(II) porphyrin/cobalt(III) corrole in the transducer layer

Disposable ion-selective electrodes of high reproducibility of recorded potentials between different sensors have been prepared using carbon-nanotubes modified paper as the transducer and electrical lead, and a poly(vinyl chloride) ion-selective membrane. The conducting paper was obtained using carboxymethylcellulose stabilized carbon nanotubes suspension – combination found to result in high stability of conventional sensors. It was shown for the first time that change of the amount of conducting material used to prepare sensor, from conventional (where it is used as transducer) to disposable sensors (where it is used as transducer and electrical lead), requiring application of much higher amount of carbon nanotubes significantly affects performance of the sensors. Presence of ions in the suspension used results in occurrence of super-Nernstian range on the potentiometric calibration curve of potassium-selective sensor, below 10−5 M KCl. Highly reproducible potential values, between sensors as well as between different calibrations, were achieved introducing mixture of cobalt (II) porphyrin/cobalt(III) corrole to the carbon nanotubes layer, at the back side of the membrane. Presence of porphyrinoids not only stabilizes potential values obtained for the sensors but also tailors ion transport through the membrane, resulting in stable potential of the sensors, although a super-Nernstian region is present on the calibration line.