Dissertation Defense Announcement
The Herff College of Engineering announces the final Dissertation of
for the Degree of Doctor of Philosophy
on March 22, 2018 at 10:00 AM in Engineering Administration 202C.
Advisor: Erno Lindner
Contribution towards ideal solid contact ion-selective electrodes: mechanistic studies, optimization, and characterization
ABSTRACT: Solid contact (SC) ion-selective electrodes (ISEs) utilizing conductive polymers (CPs) as SC 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 between the CP and the ion-selective membrane (ISM); 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 CP layers with varying degrees of hydrophobicity and controlling the redox potentials of the CPs are investigated. PEDOT(PSS)-based ISEs built on Au and GC had short equilibration times while those on Pt were significantly longer. These results were among the first to suggest that the substrate electrode|CP interface plays a significant role in the electrochemical behavior of the fully fabricated ISE. Due to the hydrophilicity and hydrogel-like properties of PEDOT(PSS), pH ISEs showed significant CO2 interference, which limits its use as a universal SC. To minimize the possibility of the formation of a thin water layer below the ISM, more hydrophobic SCs, POT and PEDOT-C14(TPFPhB) were implemented into ISEs. SC ISEs with POT as CP had unacceptable performance characteristics but following the incorporation of a TCNQ redox couple into the POT film along with adjusting the oxidized/reduced ratio of TCNQ, the ISE potential stability and equilibration time were significantly improved. However, the unacceptable potential reproducibility and light sensitivity of the CP film limited its application. PEDOT-C14(TPFPhB) was then used as a novel SC in ISEs and exhibited short equilibration times, excellent potential stability, and no light sensitivity. The superhydrophobic PEDOT-C14(TPFPhB) film eliminated the formation of any water layer and any interference due to CO2 which allows accurate pH determination in whole blood samples with fluctuating CO2 levels. These experimental results led to the conclusion that PEDOT-C14(TPFPhB) may be the ideal SC for SC ISEs requiring minimal to no calibration.