Solid-Contact pH Sensor without CO Interference with a Superhydrophobic PEDOT-C as Solid Contact: The Ultimate "Water Layer" Test.

The aim of this study was to find a conducting polymer-based solid contact (SC) for ion-selective electrodes (ISEs) that could become the ultimate, generally applicable SC, which in combination with all kinds of ion-selective membranes (ISMs) would match the performance characteristics of conventional ISEs. We present data collected with electrodes utilizing PEDOT-C, a highly hydrophobic derivative of poly(3,4-ethylenedioxythiophene), PEDOT, as SC and compare its performance characteristics with PEDOT-based SC ISEs. PEDOT-C has not been used in SC ISEs previously. The PEDOT-C-based solid contact (SC) ion-selective electrodes (ISEs) (H, K, and Na) have outstanding performance characteristics (theoretical response slope, short equilibration time, excellent potential stability, etc.). Most importantly, PEDOT-C-based SC pH sensors have no CO interference, an essential pH sensors property when aimed for whole-blood analysis. The superhydrophobic properties (water contact angle: 136 ± 5°) of the PEDOT-C SC prevent the detachment of the ion-selective membrane (ISM) from its SC and the accumulation of an aqueous film between the ISM and the SC. The accumulation of an aqueous film between the ISM and its SC has a detrimental effect on the sensor performance. Although there is a test for the presence of an undesirable water layer, if the conditions for this test are not selected properly, it does not provide an unambiguous answer. On the other hand, recording the potential drifts of SC electrodes with pH-sensitive membranes in samples with different CO levels can effectively prove the presence or absence of a water layer in a short time period.