Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 152-162).

>Magister Scientiae - MSc / Environmental pollution is always the hottest topic in public conversation and one of the most concerned aspects of human health. The thin film sputtered microelectrode devices have been developed to improve the quality of human health, by offering better monitoring capabilities. This thesis is divided into three parts and the studies were performed on chemical sensor technology currently available and under development using modified methods. In the first part of this thesis: (i) the studies are related to synthesis, characterization and polymerisation of polyaniline (PANI) and polyaniline-co-poly(2,2´-dithiodianline) (PANI-co-PDTDA). Polyaniline (PANI) and the copolymer of aniline with dithiodianiline, an aniline derivative containing S-S-links were of interest in polymer synthesis. Electrochemical synthesis was carried out in 1 M HCl and different concentrations of H2SO4 (1, 2.5, and 5 M) solutions for PANI and PANI-co-PDTDA respectively. The PANI and PANI-co-PDTDA were grown electrochemically on the surface of a glassy carbon electrode (GCE) by repetitive cyclic voltammetric scanning. Cyclic voltammetry (CV) was used to evaluate the differences between the electrochemical characteristics associated with growth of the copolymer and homopolymer, polyaniline (PANI). The surface concentration of PANI was estimated to be 2.64 × 10-1 mol.cm-2 while the film thickness was estimated to be 7.09 × 10-10cm and 1.49 × 10-9cm for scan rate and aquare root scan rate. In contrast, PANI-co-PDTDA concentrations (1, 2, 5 and 5 M H2SO4 solutions) gained a surface concentration (G) falling in the range 6.1 x 10-2 - 7.9 x 102 mol.cm-2 and a film thickness in the range 8.16 x 10 -9- 2.05x10-8cm. The second section of this thesis focused on the development of two sensors, Pt/PANI/HRP and Pt/PANI-co-PDTDA/HRP biosensors. The biosensor described in this chapter focus on the use of horseradish peroxidise (HRP) with hydrogen peroxide as substrate, was constructed with the aim of further investigation of inhibition by heavy metals (Cd2+, Pb2+ and Hg2+). To achieve this, the enzyme HRP as the catalytic bio-element, was immobilised on the surface of a platinum electrode with PANI as a mediator. Immobilisation of HRP in conducting polymer matrices of PANI and PANI-co-PDTDA were achieved by electrochemical polymerisation. The use of amperometric detection allowed for the coupling of the biosensor with a portable potentiostat system (PalmSens). Differential pulse voltammetry (DPV) as technique was used as a detection method for inhibition determination. Selection of suitable pH values for biosensor performance was evaluated and the system showed optimal performance at pH 6.8 and 7.2 for Pt/PANI/HRP and Pt/PANIco- PDTDA/HRP biosensors, respectively. The biosensors developed in this work showed detection limits (LODs) of 0.32 mM and 0.0483 mM for PANI/HRP and PANI-co- PDTDA/HRP, respectively. For the Pt/PANI/HRP biosensor, the apparent Michaelis-Menten constant (Km app) value and maximum current (Imax) were evaluated from Lineweaver-Burk plots at various H2O2 concentrations. The values were found to be 0.6 mM and 1.7 μA for the Pt/PANI/HRP biosensor, while for the Pt/PANI-co-PDTDA/HRP biosensor the results were 0.7 mM and 0.27 μA, respectively. The third section investigated the adsorptive cathodic differential pulse stripping voltammetric (AdDPSV) determination of platinum group metals (PGMs), using an ex situ bismuth coated screen printed carbon electrode (SPCE/Bi) as the working electrode and ammonium buffer solution (pH = 9.2) as the supporting electrolyte. The cathodic stripping differential pulse method was used for investigating the electrochemical behaviour and the quantitative analysis of platinum group metals (Pt, Pd and Rh) at the SPCE/Bi surface in the presence of dimethylgloxime (DMG) as a complexing agent. In order to determine the metals at improved detection limits ensuring repeatability and sensitivity, a complete optimization study of voltammetric parameters was performed. The proposed method was successfully applied to the determination of the real samples (sediments & water) collected in the platinum mining area in the North-West and Limpopo Provinces, South Africa. The results were compared with those obtained by the glassy carbon bismuth film (GC/BiF) voltammetric and ICP-AES spectrometry techniques. Well-shaped voltammograms with clear peak potentials were obtained in the analysis of the real samples, offering excellent perspectives on the use of the constructed modified electrodes. The calibration curves for all PGMs investigated were linear with the limit of detection (LOD) at approximately 0.008, 0.006, and 0.005 μg.L-1 for Pd, Pt and Rh, respectively.

The promoter region of the katG gene of Escherichia coli has been fused to two reporter genes GFPuv, encoding green fluorescent protein derived from Aequorea victoria and luxCDABE, encoding bacterial luciferase, from Photorhadbus luminescens to compare the qualities of these two reporters in microbial biosensor applications. In Escherichia coli both reporter systems produce stable signals. The lux construct was more sensitive at lower concentrations of hydrogen peroxide and the response time was shorter when compared with GFPuv. The latter, however, was better able to sense oxidative stress at concentrations that impaired signal output in the E. coli lux system. Low level non-induced bioluminescence was observed using the P. luminescens reporter system and this was utilised to measure EC50. As many compounds produce an increase in luminescence when incubated with this system, there is no means of specifically identifying any oxidative pollutants in the unknown sample. The system is limited to compounds that produce oxidative stress. Here we describe a system to add specificity to the stress-response whole-cell biosensor using glucose oxidase, which produces from glucose, hydrogen peroxide and gluconate. On incubation of these two adjuncts, glucose and glucose oxidase, with the pkatGlux whole cell biosensor, we found that the system was specific for glucose and had a range of sensitivity from 2 to 12 mM glucose. We propose that by adding glucose oxidase to the oxidative stress whole cell biosensor the specificity of the oxidative stress response can be increased, and by adding other oxidase enzymes the range of compounds that can be detected is expanded. There are enzymes of which the products of metabolism include glucose, beta-galactosidase converts lactose into glucose and galactose. The enzymes, beta-amylase and beta-amlyglucosidase digest starch to produce glucose and cellulases that act on cellulose to liberate glucose. Glucose oxidase then converts glucose to hydrogen peroxide and gluconate, the latter of which induces an increase in luminescence from the E. coli lux system. Thus it is possible to further develop the theme of adding in specificity to the stress response whole cell biosensor in the use of dual enzyme systems, where the first enzyme acts on the first substrate to yield glucose on to which glucose oxidase can metabolise, to yield hydrogen peroxide. If pkatGlux is incubated with a dual enzyme system then the number of compounds that can be biosensed can be increased and a greater specificity introduced. Samples may originate from lake, river or soil samples. These will not be 'clean'; they may contain organic debris, dirt and other bacteria that could interfere with the biosensing process. To this end lake and soil samples were spiked with substrates to see if direct sensing is possible, without the need for sample preparation. It was indicated that biosensing could take place in samples that originated from an aqueous environment. Where there were high levels of soil present, luminescence signal was quenched, which was restored on extraction of the substrate with appropriate solvent.

Polydiacetylenes (PDAs) exhibit a chromatic response to solvents, temperature, strain and other environmental perturbations. When formed in a solid-state polymerization, the backbone of the polymer is planar which provides extended conjugation polymer backbone. However, when an external force is exerted on the backbone, the extended conjugation is interrupted and an optical shift from blue to red is observed. A system using conjugated PDA Nano structures has been developed as a model to study the reversibility in the fluorescence resonance energy transfer (FRET) and electronic absorption of the PDA liposome particles. In the first study, a reversible system composed of PDA and Sulforrhodamine-101 was utilized where PDA and SR -101 act as acceptor and donor respectively. Colorimetric transition from blue to red in PDA liposomes was achieved through heating the conjugated liposomes. In this work, the FRET mechanism was evaluated without violating the role of nature that energy flows "down" hill and that the role of donor and acceptor in FRET are fixed. Reversible interchanging roles of donor and acceptor over many thermo-chromatic cycles in a modified-PDA-SR101 liposomal system were also evaluated. The nanotubes synthesized are thus unique and robust. The characterization studies showed that the nanotubes are both in Nano and micro scale. Thus the self-assembled chemistry using this material would find wide applications in such areas such as sensors, actuators, and computational devices at both micro and nano scale and further studies might offer them as an encapsulation drug delivery vehicle. Both these studies offer a new insight to the unique properties of polymerized PDA liposomes.

Given their widespread effects and distribution in both natural and industrial environments, the monitoring of phenolic compounds is of considerable analytical interest. Electrochemical biosensor technologies, in particular those comprising laccase enzymes, afford many potential benefits to address this analytical need. However, several key factors affecting sensor response currently limit their applicability. This Thesis reports on the fabrication and optimisation of an electrochemical laccase-based biosensor towards the application of the monitoring of phenolic compounds. Selected factors considered to affect sensor response were investigated using the optimised biosensor. These included: electrochemical, biochemical and substrate-dependent factors, which were found to intersect in modulating biosensor response signals. Through the application of transducer-dependent and substrate-dependent parameters, the selective and simultaneous detection of a mixture of different phenolic analytes is successfully demonstrated. This Thesis also investigates the use of Quartz-Crystal Microbalance with Dissipation (QCM-D) technology, an analytical technique that measures physical parameters of thin-film structures, towards the successful monitoring of enzyme immobilisation strategies. These strategies are fundamental to the successful fabrication of biosensors, and the real-time monitoring of immobilised film formations is of considerable research interest. In the studies reported on in this Thesis, QCM-D technology was demonstrated to be an effective complementary technology in the prediction of film immobilisation techniques on the resultant biochemical kinetics of immobilised enzymes.

No description available.

Diagnostic biosensors are on the rise in the global market due to the increasing prevalence of diseases. Specifically, the point-of-care segment has made great strides due to the improvement of biosensors' user-friendliness, simplicity, and clinical capabilities in the comfort of one's home. Although there are conventional diagnostic techniques, they are mutually time-consuming, costly, and labor-intensive. Not to mention, they are primarily dependent on bench-top or large immovable equipment. The widespread availability of smartphones has potentiated optical biosensors towards delivery of rapid and point-of-care diagnostic biosensors. Due to the affordability and user-friendliness of smartphones, smartphone-based biosensors may become ubiquitously available. Additionally, microfluidic platforms possess small footprints and portability towards development of true point-of-care and real-time diagnostic biosensors. In this dissertation, development of multiple diagnostic biosensors on microfluidic platforms is discussed. Diagnostic biosensors equipped with a smartphone-based optical detection show great promise of bringing clinical and bench-top laboratory capabilities for the convenience of the user, with reduced time, costs, and labor requirements. The widespread availability of point-of-care and real-time diagnostic biosensors may show promise in securing global health.

No description available.

A computational investigation of some optoelectronic applications of carbon nanotubes (CNT) is presented, including CNT-based solar cells and biosensors. The results could be used to evaluate the performance of CNT devices and clarify the necessity of further experimental research in this area. A coaxially-gated CNT field-effect transistor (CNFET) forms the basic structure of the devices modeled in this thesis. Diffusive transport is present in long-channel devices, as in our case, while the quantum mechanical effects are mainly present in the form of tunneling from Schottky-barrier contacts at the metal-CNT interfaces. Band-to-band recombination of electron-hole pairs (EHP) is assumed to be the source of electroluminescence. In a first-order approximation, protein-CNT interactions are modeled as the modification of the potential profile along the longitudinal axis of CNTs due to electrostatic coupling between partial charges, in the oxide layer of the CNFET, and the nanotube. The possibility of electronic detection is evaluated. The electroluminescence of the CNT is proposed as an optical detection scheme due to its sensitivity to the magnitude and the polarity of the charge in the oxide. The validity of the model is argued for the given models. A value for the minimum required size of a computational window in a detailed simulation is derived. The structure of an electrostatically gated p-i-n diode is simulated and investigated for photovoltaic purposes. The absorbed power from the incident light and the interaction between the nanotubes is modeled with COMSOL. The results are interpreted as a generation term and introduced to the Drift-Diffusion Equation (DDE). We have observed behavior similar to that in an experimentally-realized device. The performance of CNT-based solar cells under standard AM 1.5 sunlight conditions is evaluated in the form of an individual solar cell and also in an array of such devices. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

In the forensic DNA field, quantitative PCR (qPCR) is commonly used to quantify the amount of deoxyribonucleic acid (DNA) in evidentiary samples. Though sensitive, this method is prone to error. Electrochemistry-based biosensors have been described as a possible alternative to qPCR. To this end, this work aims to develop a biosensor for forensic quantification by chemisorbing oligonucleotides functionalized to methylene blue onto the surface of gold screen-printed electrodes. Prior to this, the surface characteristics of the screen-printed gold electrode are examined through the use of a well-known redox probe Ru(NH3)62+/3+. Cyclic voltammetry (CV) and Square Wave voltammetry (SWV) were used to measure the current signal. The Randles-Sevčik equation was used to relate the area of the electrode with the current signal. Surface examinations of the gold screen-printed electrodes suggested these electrodes are suitable for use as a forensic DNA biosensor. Attempts to bind the oligonucleotide to the gold electrode were conducted. Though binding was successful, the resultant SWV signal suggested methods to chemisorb DNA onto gold surfaces require optimization.