Chemistry - Doctoral Theses

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    Laser fabrication of porous, 3D graphene-like carbon from polyimide and sustainable bioplastics
    (University College Cork, 2022-06) Larrigy, Cathal; Quinn, Aidan J.; Iacopino, Daniela; Science Foundation Ireland
    Laser-induced graphitization (LIG) of materials provides a unique and advantageous method for fabrication of 3D, porous, conductive, carbon structures with high surface area. By using laser-irradiation of target substrates, conductive patterns such as electrochemical or chemiresistive sensing elements can be fabricated additively, thus reducing both the energy footprint and cost. However, typically LIG is fabricated on non-sustainable feedstock substrates, most commonly polyimide. Studies toward using alternative and more sustainable substrates have been researched, and in this thesis one such alternative is explored, chitosan-based laser-induced graphene. This thesis aims to show the possibilities of laser-induced graphene fabrication, in examining first the fabrication of LIG on polyimide using a low-cost hobbyist 405 nm laser engraving machine, as an alternative low energy intensive fabrication method. Following this the possibility of using a more sustainable substrate as a target precursor for laser-induced graphitization in the form of a chitosan-based LIG. Finally, a potential application using chitosan-based LIG was demonstrated in the form of chemi-resistive 2-terminal impedance devices for sensing humidity and volatile organic compounds.
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    Development and characterisation of macro-disc and micro-band electrodes for electrochemical sensing applications
    (University College Cork, 2022) Madden, Julia; Galvin, Paul; O'Riordan, Alan; Thompson, Michael; Science Foundation Ireland; Electronic Components and Systems for European Leadership
    The aim of this PhD thesis was to investigate potential next generation sensor platforms for electrochemical biosensor developments, specifically towards health monitoring applications. With increasing interest in the integration of miniaturised electrodes with minimally invasive and wearable devices, this thesis sought to explore electrodes fabricated using three different technologies for the construction of electrochemical biosensors: Silicon microfabrication, Laser scribing, and dispense printing. The first experimental section aimed to investigate the use of a single ultramicroband electrode fabricated on silicon for mediator-free glucose monitoring in bio-fluid environments. Six ultramicroband electrodes, a counter electrode and reference electrode were fabricated using standard microfabrication methods i.e. lithography and etching techniques. Glucose oxidase was selected as a model enzyme to attach onto a platinum modified gold microband electrode by electropolymerisation with an o-phenylenediamine/ß-cyclodextrin layer. The resulting microband biosensor demonstrated on-chip glucose detection in buffer based media. When applied to foetal bovine serum the sensor displayed a reduced sensitivity. The second experimental section explores the use of laser-scribed graphitic carbon for flexible sensing applications. A facile fabrication method was assessed involving electrodeposition of platinum followed by two casting steps to functionalise electrodes. This study examined the chronoamperometric response of the enzymatic lactate sensor whilst the flexible polyimide substrates were fixed at a curvature (K) of 0.14 mm-1. No noticeable change in signal response was observed in comparison to calibrations obtained with a flat substrate (K=0 mm-1), suggesting potential opportunities for sensor attachment or integration with oral-care products such as mouth swabs and mouth guards. Both laser scribed graphitic carbon and Ag/AgCl modified-laser scribed graphitic carbon were examined as reference electrodes for chronoamperometric lactate measurements. This device was applied for measuring lactate concentrations in artificial saliva and diluted sterile human serum. Finally, this study investigates the potential for a low cost additive printing tool to enable the fabrication of electrochemical sensor devices. To do this, electrodes were designed and printed onto polyimide substrates. Reproducibility between electrode dimensions was assessed using 3D microscopy. Standard electrochemical characterisation techniques were employed to study the reproducibility between electrode electrochemical response. Functionality was also assessed whilst electrodes were fixed were fixed at a curvature (K) of 0.14 mm-1. Finally, a simple casting approach was applied to the dispense printed working electrode to construct a lactate biosensor for a proof of concept electrochemical sensor demonstration.
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    Electrochemical sensors for integration on silicon
    (University College Cork, 2022-03-31) Barry, Fiona; Rohan, James; Nagle, Lorraine; Science Foundation Ireland; Analog Devices; Department of Agriculture, Food and the Marine, Ireland
    Water quality monitoring is crucial to ensure the safe consumption of drinking water by humans. It is of such importance that the UN has included a specific goal for the improvement of water and sanitation in their Sustainable Development Goals (SDG). According to the UN, a staggering 3 in 10 people are without access to safely managed drinking water. At present the standard method for water quality monitoring is by laboratory testing. These typically require transportation of the sample from source to the laboratory, additional reagents, and specialised personnel and equipment to carry out the analysis. In this thesis, electrochemical methods at micro-electrodes are explored and developed for reagent-free, point-of-care analysis that does not require the need for specialised training. The main goal of the thesis is to develop low-power micro-sensors for point-of-care analysis. To achieve this, interdigitated micro-electrodes were investigated wherein each comb of electrodes could be biased separately allowing for unique analysis opportunities. Discussed herein simulations of electrode geometries are used to establish the optimum design for the interdigitated electrode arrays. The fabricated interdigitated arrays are subsequently modified with nanoporous gold resulting in an increase in current for the detection of lead by 1.5-fold. These modified interdigitated electrodes successfully detected lead in 0.1 M acetate buffer pH 4.6 with a limit of detection of 0.43 ppb. However, issues arise when applying these electrodes to reagent-free tap water, where there is no discernible peak for lead seen below 50 ppb. To overcome this obstacle the interdigitated arrangement of the electrodes can be used to electrochemically control the pH of tap water without the need for additional reagents. This leads to the successful detection of lead in tap water to as low as 10 ppb.
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    Synthesis of novel quorum sensing inhibitors of DSF
    (University College Cork, 2022) Horgan, Conor; O'Sullivan, Tim; Irish Research Council; Higher Education Authority
    Antimicrobial resistance (AMR) has become a growing concern among the medical community with many previously effective antibiotics losing their efficacy. Much of this AMR is thought to stem from biofilm formation controlled by cell-to-cell signalling. Chapter 1 introduces quorum sensing with a particular focus on the Diffusible Signal Factor (DSF) family of autoinducers. Given that these molecules contain a carboxylic acid, this chapter also contains a review of the literature relating to carboxylic acid bioisosteres which have emerged since 2013. Quorum sensing interference is an increasingly attractive target for combatting bacterial infections. Accordingly, the work in this thesis focusses on the synthesis of sulfonamide-based bioisosteric derivatives of Burkholderia DSF (BDSF). In Chapter 2, 15 novel N-acyl sulfonamide analogues of BDSF are prepared and tested for biological activity. Some of these compounds display significant activity against many strains of bacteria both in vitro and in vivo. The cis-α,β-unsaturated double bond, a key factor in the biological activity of BDSF, is susceptible to isomerisation. The preparation and subsequent biological evaluation of 16 potentially more stable aromatic N-acyl sulfonamide analogues of BDSF is detailed in Chapter 3. Many of these compounds significantly inhibited biofilm formation and enhanced the efficacy of last-resort antibiotics against S. maltophilia and B. cenocepacia. In Chapter 4, X. fastidiosa, a bacterium responsible for diseases such as olive quick decline syndrome, is introduced. Some of the aromatic N-acyl sulfonamide analogues inhibited the formation of biofilm biomass and cell growth in the bacterium. The synthesis and subsequent testing of the parent signalling molecules and aromatic analogues containing a longer alkyl chain is also described. A practical synthetic route to a new class of aryl sulfonamide analogues of BDSF is presented in Chapter 5. Using SwissADME and MarvinSketch, important ADME properties of a virtual library containing 16 potential aryl sulfonamides, and the pre-existing olefinic and aromatic N-acyl sulfonamides are analysed to determine their suitability as drug candidates.
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    SMARTProbe, a needle integrated with a portable handheld impedance analyser for real-time breast disease detection
    (University College Cork, 2022-05) Ugwahy, Anulika Justina; Moore, Eric; O'Donnell, Brian; O'Sullivan, Martin; Irish Research Council for Science, Engineering and Technology; Cork Academy of Regional Anaesthesia
    Breast cancer is common, affecting 2 out of 10 women with a suspicious lesion. There is no real-time preoperative diagnosis for breast disease. The triple assessment for detection includes a self/clinical breast examination, a mammogram, and an ultrasound-guided biopsy with histological evaluations. Different technologies are being researched to enhance the diagnostic pathway. The addition of novel technology to existing diagnostic tools and processes might provide greater diagnostic accuracy and expedite the time to arrive at a definitive diagnosis. Bioimpedance is a fast, non-destructive technique that can be investigated for real- time detection of breast disease. Alterations in the electrochemical properties of the breast, which occur with metaplastic and neoplastic cellular proliferation, can be identified and monitored using bioimpedance. Impedance measurements can give quantitative information and a signature of the electrical properties of tissue. The current clinical pathway review identified that the biopsy procedure could be improved. The design and fabrication of sensors on a Core Needle Biopsy were explored to evaluate the electrical properties of breast tissue. Nanoscale imaging and composition analysis of sensor surfaces were used to investigate the fabricated sensors. Electroanalytical characterisations of the needle sensors were performed in solutions of known concentrations. Tissue-mimicking breast phantoms were developed and interrogated with the device developed. A prototype integrating the needle sensors and a 3D printed biopsy firing mechanism was achieved. The clinical investigation of the excised breast tissue using the developed sensors was conducted at the Cork University Hospital (CUH). The bioimpedance sensor evaluated the differences in the electrical properties of excised healthy and diseased breast tissue. The results were analysed, and a preliminary prediction model examined the discriminatory ability of the device. The bioimpedance results for excised tissue type were correlated with histological reports. Hence, this research contributes to the proof of concept in ex-vivo breast tissue that will guide the in-vivo clinical investigation. The future work required to demonstrate the technology in a real-space environment is also detailed. This biomedical prototype designed, fabricated, and characterised in this thesis is called the SMARTProbe. The SMARTProbe's novelty lies in being a hand-held biopsy system with a tissue discrimination function. Commercially available pre-and intra- operative technologies in breast disease management are not miniaturised like the SMARTProbe. The device can be easily adapted to the current clinical diagnostic pathway to provide more information on tissue type at the needle location during a biopsy procedure. It is envisaged that the device will enhance representative sampling, reducing the number of cores taken. The technology will improve the biopsy procedure for both the patient and the radiologist. The different processes used in the fabrication process are easily translated to large scale manufacturing as they are already used in the biomedical device industry.