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http://hdl.handle.net/11375/25909
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DC Field | Value | Language |
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dc.contributor.advisor | Hoare, Todd | - |
dc.contributor.author | Lu, Yang | - |
dc.date.accessioned | 2020-10-13T02:43:58Z | - |
dc.date.available | 2020-10-13T02:43:58Z | - |
dc.date.issued | 2020 | - |
dc.identifier.uri | http://hdl.handle.net/11375/25909 | - |
dc.description.abstract | Biosensors, as a potential diagnostic tool contributing to next-generation medicine, have been continuously researched and optimized to achieve improved performance with lower cost. Among them, electrochemical sensors coupled with multi-functional polymers have attracted particular attention because of their ability to provide real-time, quantitative, and highly-sensitive analysis. For example, appropriate polymers can enhance the bioavailability of an immobilized biomolecule or recognition elements and/or facilitate lower limits-of-detection when used as a coating. In this thesis, magnetic microgel beads and ion-conductive polymers were fabricated to serve as anti-fouling bioactive immobilization platforms. Magnetic microgel beads are routinely used in biosensing and bioseparation applications given their high surface area for immobilization (and thus high capacity to capture biomolecules) coupled with their facile separation from suspension using a magnetic field. However, current magnetic beads are typically based on silica or polystyrene and thus have relatively poor protein-repellent properties, leading to enhanced binding of non-target molecules and thus reduced signal:noise ratios. In response, magnetic microgel beads based on the highly protein-repellent polymer poly(oligo(ethylene glycol) methacrylate (POEGMA) were fabricated using a semi-batch inverse emulsion polymerization. The resulting microgel beads have a narrow size distribution centred around ~5 μm, a low level of aggregation, and high colloidal stability, all at a low cost. Effective magnetic separation can be achieved within five minutes, while the inherent protein-repellent properties of POEGMA significantly reduce non-specific protein adsorption. Upon using carbodiimide chemistry to tether a methylene blue-linked DNAzyme to the microgel bead that is selectively cleaved in the presence of E. coli, a 6.3-fold higher signal was measured upon exposure to E. coli in buffer and a 97-fold higher signal retention was achieved in clinical urine (based on the electrochemical detection of released methylene blue from capture probes) relative to that achieved with Dynabeads®, a leading commercial magnetic bead. To reduce non-specific adsorption on gold electrodes without compromising the conductivity and thus signal:noise of the electrochemical device, three types of water-soluble polymers were synthesized and tested for their anti-fouling performance and conductivity when coated on gold electrodes. POEGMA polymer functionalized with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) failed to show sufficient conductivity, while POEGMA polymer functionalized with thiol groups that bound directly to the gold electrode maintained sufficient ion conductivity but reduced the DNA signal at the desired voltage (as generated by hybridization between cleaved probes from DNAzyme and capture probes grafted on electrodes). The possible explanation is that the capture probes were not immobilized on polymer efficiently because of the reversibility of imine bonds formed between amine labelled probes and aldehyde groups from polymer. Zwitterionic polymer poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide] (PDMAPS) functionalized with thiol groups enhanced the conductivity of the electrode (showing a lower resistance to ion conductivity even compared to the bare electrode), although further optimization is still required to realize higher DNA signals for clinical applications. Overall, both magnetic beads microgels and conducting non-fouling polymers enabled significantly improved performance of electrochemical biosensors for E.coli detection. Magnetic microgel beads show potential for commercialization in the future. | en_US |
dc.title | Engineering Hybrid Polymer Materials for Enhanced Biosensing | en_US |
dc.type | Thesis | en_US |
dc.description.degreetype | Thesis | en_US |
dc.description.degree | Master of Science in Biomedical Engineering | en_US |
dc.description.layabstract | Electrochemical biosensors are analytical devices that convert the signal of a biological reaction into an electrochemical signal and are used in a range of clinical, pharmaceutical, agricultural, and food applications. Since their first development, scientists have put many efforts into designing smaller, more accurate, and more automated biosensors. One approach for achieving these goals is through the integration of various types of polymers. Magnetic microgels, crosslinked three-dimensional polymer networks containing entrapped magnetic materials, are demonstrated to help achieve these goals by carrying higher quantities of biological components relative to two-dimensional surfaces while being separable easily with a magnet after the sensing reaction is complete. To satisfy the end-use, magnetic microgels with optimal size, stability, magnetization properties, and functionality were designed in this project. Another general focus in the area of biosensors is to achieve detection of targets without the need to pre-process the source sample (e.g. blood, urine, saliva, etc.) prior to analysis. However, most in-field biosensors have to work with untreated clinical samples and thus generate noisy or low-resolution signals. Polymer can play an important role in reducing this interfering signal by preventing the interfering molecules from approaching the detector. While coating the detector with a highly water-loving polymer can minimize such interference, such polymers are typically non-conductive and as such also block the desired signal from target binding. Therefore, thin layer polymer coatings were designed and optimized to repel interfering molecules without influencing the detection of targets. | en_US |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Yang Lu-finalsubmission2020Sept-MASC Thesis.pdf | 2.73 MB | Adobe PDF | View/Open |
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