The evaluation, analysis and development of an oxygen-insensitive amperometric glucose biosensor and its application in microbial batch culture are described. The biosensor consisted of a graphite foil electrode modified with glucose oxidase and 1,1'-dimethylferrocene, and operated via mediated electron transfer from the enzyme to the electrode. Initial evaluations illustrated several operating characteristics which would be expected to cause problems in continuous monitoring applications, most notably sensor instability and a progressive increase in response time. The main underlying causes of these unfavorable characteristics were identified as enzyme loss, mediator loss and substrate diffusion limitation within the electrode. As a consequence of these insights, further development of the sensor was undertaken. A number of different electrode materials and enzyme immobilization techniques were tested, resulting in the development of a novel immobilization procedure using a hexadecylamine coating to bind 'the activated carbohydrate residues of periodate-oxidized glucose oxidase. This improved the sensor lifetime and response time under continuous operation. Strategies for the reliable application of the biosensor in fermentation monitoring were evaluated. In-line flow cell and in_§itu membrane probe approaches were considered, and the latter approach was preferred: Considerable attention was devoted to optimising the design of such probes. The best design accommodated a three electrode configuration with a multiple biosensor array. It was found necessary to allow for periodic on-line calibration within the aseptically operating probe. This configuration was successfully applied on-line to monitor glucose in batch cultures of Escherichia coli.

An amperometric glucose biosensor was fabricated using electospun polyaniline fibers. Polyaniline was reacted with camphorsulfonic acid to produce a salt, which was then dissolved in chloroform containing polystyrene. Using this solution, fibers were formed and collected by electrospinning. Glucose oxidase was immobilized onto these fibers using an electrostatic layer-by-layer adsorption technique. In this method, poly(diallyldimethylammonium chloride) was used as the counter ion source. The level of adsorption was examined and evidence of layer-by-layer adsorption was obtained using a quartz crystal microbalance technique. A biosensor was fabricated from these fibers as a working electrode, and used to measure the glucose concentration accurately.

<p>Two thirds of patients with diabetes avoid regularly monitoring their blood glucose levels because of the painful and invasive nature of current blood glucose detection. As an alternative to blood sample collection, exhaled breath condensate (EBC) has emerged as a promising non-invasive sample from which to monitor glucose levels. However, the inconsistency in the methods used to collect EBC significantly impacts the reliability of reported analyte concentrations in EBC. Furthermore, this dilute sample matrix requires a highly sensitive glucose biosensor to enable robust and accurate glucose detection at the point-of-care. Together, a reliable collection method and sensitive detection system can enable accurate modeling of glucose transport from blood to breath that is reflective of airway glucose homeostasis.</p> <p> I address this research gap by simultaneously designing a standardized EBC collection method that allows for separation of dead space and alveolar air and developing a competitive fluorescent biosensor that can resolve micromolar glucose concentrations changes. First, I develop a low-cost, automated condenser that selectively collects exhaled breath that has been exchanged with lung fluid based on the detection of higher breath temperatures that are characteristic of the lower respiratory regions. Using this device, I investigate the relationship between blood and EBC glucose in diabetic and normoglycemic human subjects. Next, I engineer the exquisitely sensitive <i>E. coli</i> glucose binding protein (GBP) with a chemo-enzymatic tag to selectively conjugate it to highly photostable quantum dots (QDs). Finally, I take advantage of the competitive binding of glucose (K_D=0.35 µM) and galactose (K_D=1.4 µM) to GBP to develop a fluorescent glucose biosensor using the GBP-QD conjugate.</p>

<p>Single-walled carbon nanotubes (SWNTs) are of special interest in current research due to their extraordinary mechanical, electronic and optical properties. Their unique structure, remarkable thermal and electrical conductivity, and high mechanical strength make SWNTs viable candidates for a wide range of device applications. However, pristine CNTs are not dispersible in most solvents, the main difficulties in CNT applications are related to their purification and solution-phase processing. In recent years, the supramolecular functionalization of SWNTs with conjugated polymers has received significant attention. Research within this field has been driven by the desire to find polymer structures that can selectively disperse certain nanotubes species with high efficiency.</p> <p>After a brief overview of the studies that are related to the investigation of the supramolecular interaction between various conjugated polymers and SWNTs (chapter 1), the synthesis of fluorene and thiophene-based conjugated polymers and their supramolecular complex formation properties with SWNTs are described (chapter 2, 3, 4, 5 and 6). In order to understand the effect that conjugated polymer structure has on formation of supramolecular complexes with SWNTs, various factors were investigated by: (1) altering the polymer backbone composition; (2) varying the polymer molecular weight; (3) introducing different solubilizing groups while the polymer backbone remained the same; (4) changing the polymer conformation. All of the resulting polymer-nanotube assemblies exhibit excellent solution stability in THF in the absence of excess unbound free polymer. The spectroscopic characterization of the polymer-SWNT complex materials indicated that the interaction between the conjugated polymers and SWNTs is strongly influenced by polymer structure.</p> <p>The interaction between a water soluble polythiophene derivative, poly[3-(3-N,N-diethylaminopropoxy)-thiophene] (PDAOT), and SWNTs is discussed in chapter 7. It is also demonstrated that the PDAOT-SWNT complexes form stable aqueous solutions that can be used for the fabrication of highly sensitive amperometric glucose biosensors.</p> / Doctor of Philosophy (PhD)

Proteins possess a broad range of structural and functional properties and, therefore, can be employed in a variety of biomedical applications. While a good number of protein-based biosensing systems and biosensors for target analytes have been developed, the search for versatile, highly sensitive and selective sensors with long term stability able to provide fast detection of target analytes continues to be a challenge. To that end, we now report the design and development of modified proteins with tailored characteristics and their further utilization in the development of biosensing systems. We take advantage of binding proteins that undergo a change in conformation upon binding to their respective target ligand analytes for the development of highly selective biosensing systems. The first class of binding proteins that was explored for this purpose was antibodies. A non-canonical site in the variable region of a monoclonal antibody was tagged with a fluorescent probe to sense the binding of analyte to its corresponding antigen-binding site. The strategy employed for designing antibodysensing molecules is universal as it can be employed for sensing any biomolecule of interest provided that there is an available antibody against the target ligand analyte. In a second strategy, we utilized designer glucose recognition proteins (GRPs) that were prepared by incorporation of unnatural amino acids in the glucose/galactose binding protein (GBP) of Escherichia coli and its truncated fragments. By taking advantage of the global incorporation method, we were able to fine-tune the binding affinity and thermal stability of the proteins, thus, allowing for the development of a reagentless fluorescence based fiber optic glucose biosensor capable of monitoring glucose in the hypoglycemic, normal, and hyperglycemic range, as well as in the hypothermic and hyperthermic temperature range.