Abstract
Non-invasive diagnostics are gaining prominence due to their ability to seamlessly monitor physiological changes over a person's lifetime and positively impact decision-making, lifestyle choices, and habits. Contact lenses, being one of the most common wearable devices, offer a unique platform for the non-invasive monitoring of analytes in the tear fluid. Ophthalmic biomarkers have been identified as a promising route for disease detection. However, challenges in developing these complex technologies lie in having to match the strict requirements of contact lenses with that of the diagnostic device. Moreover, achieving high sensitivity in order to sense analytes in the range of ophthalmic analyte concentrations is of upmost importance.Ti3C2Tx MXene is a two-dimensional material that has been incorporated in several diagnostic technologies with reported enhanced sensitivities and limits of detection. Electrochemical sensors typically take advantage of their high conductivity, redox-active surfaces, and easy processability. However, only complex composites or electrode coatings have investigated the performance of Ti3C2Tx. Therefore, the optimisation of Ti3C2Tx towards electrochemical sensing is limited. Moreover, pristine Ti3C2Tx possesses several properties that may result in the development of unique sensors which have yet to be explored.
The objective of this thesis was to showcase the potential of Ti3C2Tx MXene as a pristine electrode for the detection of ophthalmic biomarkers. Initially, a fabrication protocol was developed for creating pristine Ti3C2Tx electrodes, eliminating the need for current collectors or other electroactive materials. The MXene electrode was characterised using ruthenium hexamine as the outer sphere standard probe. Electrode optimisation for electron transfer was achieved by employing large MXene flakes and thin electrode thickness, resulting in an increase in the ratio between faradaic and capacitive currents in cyclic voltammograms. Additionally, the successful demonstration of flexible and transparent electrodes without compromising the electrochemical signal was achieved for the first time.
Subsequently, electrode optimisation for hydrogen peroxide, as a relevant reactive oxygen species in the tear fluid, detection was performed. It was observed that smaller flake sizes exhibited the highest sensitivity to hydrogen peroxide. The sensitivity to hydrogen peroxide was found to be independent of electrode thickness, highlighting the potential of thin MXene films for transparent sensors. Furthermore, an investigation into optimising the electrochemical parameters revealed that the highest sensitivity for hydrogen peroxide detection was achieved at -1050 mV vs Ag|AgCl. Importantly, no interference was observed from other potential interferent agents present in tear fluid, underscoring the selectivity of Ti3C2Tx for hydrogen peroxide detection at this potential. Finally, the pristine Ti3C2Tx electrode was successfully incorporated into a commercially available contact lens as a proof of concept. Contact angle measurements confirmed the hydrophilicity of Ti3C2Tx, resulting in increased wettability of the lens. The stability of the coating in storage contact lens solution and simulated tear fluid was demonstrated. The cytocompatibility of Ti3C2Tx-coated contact lenses was evaluated using a human corneal epithelial cell line, showing no significant differences between large and small flakes. Ultimately, the successful detection of hydrogen peroxide using a transparent and flexible pristine Ti3C2Tx sensor incorporated into the lens was demonstrated.
Overall, this thesis establishes the potential of Ti3C2Tx MXene as a promising material for ophthalmic biomarker detection, showcasing its excellent electrochemical performance, selectivity, stability, and compatibility as an electrode incorporated into commercially available contact lenses.
| Date of Award | Apr 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Susan Sandeman (Supervisor), Marcus Dymond (Supervisor), Yury Gogotsi (Supervisor) & Bhavik Patel (Supervisor) |