Electronic Theses and Dissertations

Contribution Towards Ideal Solid Contact Ion-Selective Electrodes: Mechanistic Studies, Optimization, and Characterization

Jennifer Marie Jarvis

Data is provided by the student.


Solid contact (SC) ion-selective electrodes (ISEs) utilizing conductive polymers (CPs) as ion-to-electron transducers are plagued with poor potential stability, sensor-to-sensor standard potential reproducibility, and long equilibration times which hinders their use as minimal calibration or calibration-free sensors for clinical diagnostics. Some imperfections in the SC sensor performance are thought to be due to the presence of an undesired water layer beneath the ion-selective membrane; a result of the unsatisfactory hydrophobicity of the CP layer. The time-dependent change in the redox potential of the CP layer is the other major factor. To address these issues, in this work, the benefits of the implementation of highly hydrophobic CP layers with controlled redox potentials are investigated.ISEs built with PEDOT(PSS) as SC on Au and GC had short equilibration times while those on Pt had sluggish equilibration. These results were among the first to suggest that the substrate electrode|CP interface plays a significant role in the electrochemical behavior of the SC ISE. Due to the hydrophilicity and hydrogel-like properties of PEDOT(PSS), pH ISEs with PEDOT(PSS) as SC showed significant CO2 interference, which limits its use as a universal SC. To minimize the CO2 interference, PEDOT(PSS) was replaced by POT and PEDOT-C14(TPFPhB) as ion-to-electron transducers in SC ISEs. SC ISEs with POT as SC had unacceptable potential reproducibility partly due to the significant light sensitivity of the POT film. However, the performance characteristics of the POT-based sensors were significantly improved through the incorporation of a TCNQ redox couple into the POT film along with adjusting the TCNQ oxidized/reduced ratio. In contrast to the POT-based SC ISEs, electrodes with the superhydrophobic PEDOT-C14(TPFPhB) as SC exhibited short equilibration times, excellent potential stability, and no light sensitivity. In addition, the PEDOT-C14(TPFPhB) film eliminated CO2 interference, which has been experienced with PEDOT(PSS) as SC. Consequently, the pH sensors with PEDOT-C14(TPFPhB) as SC allow accurate pH determination in whole blood samples with fluctuating CO2 levels. In summary, the data collected with PEDOT-C14(TPFPhB)-based SC K+, Na+, and pH sensors suggest that PEDOT-C14(TPFPhB) may be the ideal SC for SC ISEs which may lead to ISEs requiring minimal to no calibration.