Development of on-farm diagnostic devices
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Date
2020
Authors
Robinson, Caoimhe
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University College Cork
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Abstract
The global population, currently 7.7 billion, is expected to grow to 9.7 billion by 2050. This is expected to lead to a 70% increase in demand for animal-based protein. Irish beef and dairy products account for over 50% of our agricultural output and DAFM’s Food Wise 2025 strategy aims to position Ireland as a world leader in sustainable agri-food production. However, the high percentage of livestock that are lost due to infectious diseases (20%), poses a challenge to achieving this sustainability, in addition to more sustainable use of antimicrobials, smarter livestock diagnostics and treatments are therefore required. The goal of this thesis was to develop a low-cost disposable biosensor that would permit point-of-care (POC) detection of diseases in bovines, through cost-effective, scalable microfabrication techniques. Such devices could enable real-time determination of the health status of animals on farm and contribute to more informed therapeutic interventions. Electrochemistry presents a viable option for POC devices in this regard and allows easy integration with portable electronics.
Electrochemical Impedance Spectroscopy (EIS) is a surface sensitive technique that measures the resistive and capacitive behaviour of an electrochemical system. It lends itself to serological immunosensor development as it allows label-free detection. For the purposes of this research, silicon devices were fabricated with six microband working electrodes, gold counter, and platinum pseudo-reference electrodes. The microband working electrodes were modified with a biocompatible co-polymer. This co-polymer supported the cross-linking of a bioreceptor (e.g., anti-bovine IgG) to electrode surface, which selectively bound to the target biomolecule (bovine IgG) in serum. This EIS device could distinguish between seronegative and seropositive samples in 15 minutes making it suitable for POC applications. Additionally, the presence of six working electrodes allowed for testing of multiple samples at a time. Often, however, only a single test is required. As such, silicon presents an expensive option for disposable sensors. Hence, polymer replication methods were also investigated in this thesis. This process allowed a single silicon wafer to be repeatedly used to produce polymer structures. A microneedle format was chosen to eliminate the need for taking samples on-farm and provide a pain-free method of in vivo measurements in interstitial fluid in interstitial fluid. The fabrication method used a double-sided micro-moulding process to move towards mass manufacturing. COMSOL simulations were performed to explore the active layer on the microneedle tip surface, ensuring no diffusional overlap between electrodes and providing the most effective tip design.
The microneedle structures also presented the opportunity for novel fabrication of nanoring arrays, by removing part of the protruding structure and exposing underlying nanorings. These have the potential to be highly sensitive electrochemical devices due to enhanced mass transport and high current densities, while maintaining the scalable cost-effective fabrication process of the microneedles. Devices produced steady-state CVs in a known redox molecule, with currents in the nA range.
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Keywords
Electrochemistry , Biosensor , Ultramicroelectrodes , Microneedles , Nanorings , Electrochemical impedance spectroscopy
Citation
Robinson, C. 2020. Development of on-farm diagnostic devices. PhD Thesis, University College Cork.