Subject Area
Electrical, Electronics Engineering, Computer Engineering, Bioengineering and Biomedical Engineering
Abstract
Traditional glass-rod pH sensors provide reliable pH performance but are bulky and do not allow miniaturization. The pH-sensitive membrane at the electrode tip requires intermittent calibration and is prone to membrane clogging in non-aqueous or viscous solutions. The characteristics compromise pH accuracy specifically for continuous and long-term stable applications. Clinical challenges using traditional bulky pH sensors for skin and body regulation are intermittent calibration, periodic monitoring, and labor-intensive diagnosis. Miniature pH sensors developed on flexible platforms do not require frequent calibration, allow continuous data transduction by electronic integration, and straight forward operation. To facilitate such features, researchers have engineered pH sensors by manipulating materials and detection techniques.
This dissertation focuses on the development and optimization of miniature and flexible iridium oxide (IrOx) based pH sensors for biofluid monitoring. The biocompatible and inert nature of IrOx makes it a desirable material for biosensing applications. A comprehensive literature review on IrOx pH sensors, encompassing film types, substrates, and performance factors, laid the groundwork for subsequent investigations.
To enhance sensor flexibility and compatibility with skin applications, IrOx films were deposited on porous and flexible substrates. The resulting sensors were characterized for pH sensitivity, hysteresis, and stability in controlled buffer and biofluid environments. Building upon this, flexible microwire IrOx pH sensors were integrated into meshed fabric pads for potential use in electrical bandages. Electrical measurements performed in microwells also vi demonstrated the small-volume sensing capabilities, needed for real-time biofluid sensing.
To address the challenges of viscosity and salt interference in biofluids, IrOx films were developed on flexible polyimide substrates. A comparative study with commercial pH sensors was conducted to evaluate the performance of the developed IrOx sensors. Through collaboration with a startup company, the production of IrOx sensors on polyimide substrates was mass-printed, and rigorous testing protocols were implemented. The mass-produced printed electrodes showed high reliability and repeatability based on electrical measurements among different sets of electrodes. Electrodes were further laminated and tested in flat and conformed conditions showing exceptional repeatability.
To improve long-term sensor stability, anhydrous and hydrous IrOx films were developed on a polyimide substrate. A reset technique utilizing an external DC voltage was applied to the IrOx electrodes to achieve quicker transition time and enable long-term stability. The consistency in performance metrics, including stability, sensitivity, and hysteresis, across multiple electrode batches, demonstrated robust reproducibility. Subsequent testing of electrodes in both a fresh state and after a 14-day period validated the reliability of the reset technique in improving the drifting issue. This milestone eliminates electrode dependency on the need for frequent calibration.
Finally, the pH sensor built on polyimide with good mechanical rigidity was miniaturized for subcutaneous needle insertion to enable biofluid sensing directly from tissue. This research contributes to the advancement of miniaturized IrOx pH sensor technology, paving the way for real-time, reliable monitoring in healthcare such as early Sepsis detection from the human blood.
Degree Date
Summer 2024
Document Type
Dissertation
Degree Name
Ph.D.
Department
Electrical and Computer Engineering
Advisor
Jung Chih Chiao
Number of Pages
157
Format
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License
Recommended Citation
Chawang, Khengdauliu and Chawang, Khengdauliu, "MINIATURE AND FLEXIBLE pH SENSORS BASED ON IRIDIUM OXIDE FOR BIOFLUIDS APPLICATIONS" (2024). Electrical Engineering Theses and Dissertations. 79.
https://scholar.smu.edu/engineering_electrical_etds/79