Chen, Qiulan. / "November 2010." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 140-152). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

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The effect of temperature increase on the optical excitation of Surface Plasmon Resonance (SPR) at an Ag-Si metal-semiconductor (M-S) junction at a wavelength of 1 . 1 52 pm is investigated theoretically using computer modeling in Fortran. In order to accurately quantify the SPR, the temperature dependent optical constants for Ag and Si are obtained theoretically or semiempirically , using a Drude model for Ag and previous experimentally determined equations for Si (the behavior of the optical constants for crystalline Si and doped Si are found to have very little deviation between each other for our case). An improvement in the theoretical derivation for the optical constants of Ag is obtained, maintaining self-consistency. The optical constants are utilized to quantify the reflectance of an incident wave on an M-S junction, using Fresnel equations for a four layer system. The reflectivity of the M-S junction is indicative of the surface plasmon generation. There exists much industrial interest in increasing the amount of photocurrent generation in semiconductors for a given number of incident photons. This increase in photocurrent is often referred to as enhancing the quantum efficiency (Q). It has been previously shown by many groups that there can be an appreciable enhancement of Q due to the optical excitation of surface plasmons on a Schottky barrier junction (M-S junction), although all these previous studies were done at room temperature. Hence, the studies of temperature effect of SPR at the M-S junction could lead to interesting effects for the Q as well. In this thesis, we have studied qualitatively the effect of temperature increase on the optical excitation of SPR at an Ag-Si junction. From these results we have attempted to draw inference to the possibility of the enhancement of Q at elevated temperatures for such a diode junction.

The aim of this project is to develop strategies for fabrication of carbon electrode surfaces with a view to creating stable and versatile monolayer systems for sensing and other applications. Glassy carbon (GC) electrodes have been successfully modified with versatile monolayers via the electrochemical reduction of aryl diazonium salts. The surfaces modified with diazonium salt monolayers were properly characterised by electrochemistry, AFM and XPS. The rates of heterogeneous electron transfer through organic monolayers on GC, Pyrolysed Photoresist Films (PPF) and gold surfaces have been studied using ferrocene as the redox probe. The diazonium salt monolayers created on GC surfaces demonstrated very stable ability and can serve as a good alternative to alkanethiol selfassembled monolayers on gold electrodes for sensing purposes. Tripeptide Gly-Gly-His modified GC electrodes have been successfully used as the electrochemical copper sensors and were found to be extremely stable. PPF has proved to be a good alternative to the GC electrode for the commercialisation of the fabricated electrochemical sensors. The most important and difficult task of this project is to fabricate glucose biosensors and immunosensors on carbon electrodes. The rigid and conjugated molecular wires (MW) as the efficient conduit for electron transfer, and a molecule with poly(ethylene glycol) chains (PEG) as an insulator for reducing the non-specific protein adsorption were successfully synthesised and introduced in the sensing systems. MW modified on GC electrodes can be used to explore the deeply buried active site of glucose oxidase to achieve direct electron transfer of GOx from the active centre FAD through the MW to the underlying GC electrode, and to fabricate third generation biosensors. The interface comprising mixed monolayers of MW and PEG has the ability to facilitate efficient electron transfer. A label-free immunosensor system has been successfully developed for electrochemical detection of biomolecular pairs such as biotin/antibiotin with low detection limitation based on mixed monolayers of MW and PEG modified GC electrode surfaces. In addition, a displacement assay has shown that the free biotin can compete with the attached biotin for binding antibiotin. SWNTs can be used as an alternative to MW to fabricate another label-free immunosensor system due to the high efficiency of electron transfer that SWNTs have demonstrated.

In this research, the determination of trace concentrations of heavy metal ions was investigated using peptide modified electrochemical biosensors. The biosensor has several advantages over atomic absorption spectroscopy and inductively coupled plasma mass spectrometry by offering greater simplicity in use and the possibility of determining the bioavailability of heavy metals. Oligopeptides were modified on the electrode surface through the spontaneous self-assembly of thiols on gold. Firstly, 3-mercaptopropionic acid (MPA) was self-assembled onto the gold surface followed by activation of the carboxyl groups using a combination of carbodiimide and succinimide chemistry for coupling of the N-terminus of the peptide to occur. Using this generic strategy, Gly-Gly-His was used for the determination of copper ions. Cu2+ was accumulated at the MPA-Gly-Gly-His modified electrode at open circuit potential followed by electrochemical measurements. The reduction of Cu2+ to form underpotential deposited copper in the Osteryoung square wave voltammogram was used for quantification. The influence of various factors on the performance was investigated and after the optimal conditions had been identified, the biosensor was used for Cu2+ calibration and was applied to the analysis of a real sample. For Cd2+ detection, two different peptides covalently attached to MPA were investigated, g-Glu-Cys-Gly (GSH) and His-Ser-Gln-Lys-Val-Phe, with the latter sensor exhibiting a lower Cd2+ detection limit, higher sensitivity and greater selectivity. Although the success of MPA as a peptide linker to the gold surface had been shown for the detection of Cu2+ and Cd2+, a more viable approach was necessary for the stable detection of a wider range of metal ions. A more stable self-assembled monolayer of thioctic acid (TA) was identified in which human angiotensin I was attached. This alternate modification procedure was superior to MPA-angiotensin I for Pb2+ detection in terms of stability and reusability with the drawback being sensitivity. The newly identified strategy was also applied to the determination of Ag+ using TA-methionine enkephalin modified electrodes. A sensor array for Cu2+ was also investigated as well as an extension to the simultaneous determination of multianalytes using four different modified electrodes. Combining a soft-modelling approach, the responses of Cu2+, Cd2+ and Pb2+ could be deconvoluted.

The purpose of the thesis is to design and develop a network of automated, distributed, living cell-based sensors, called CytoSensors. Their main role is to detect a variety of biological and chemical toxins. The system is designed to help researchers to carry out multitude of experiments, in order to build a practical knowledge base in toxin detection. The network is developed in accordance with industry standards, to be used and deployed for prevention in inhospitable environments such as battlefields, toxic urban locations or polluted agricultural regions. The sensor is composed of a processing unit (processor and memory), an archiving unit (permanent data storage), a communication unit, input devices attached to a data acquisition unit, and control devices. The CytoSensor is specifically designed to acquire and analyze visual information about the living cells: hence cameras are used as input devices and frame grabbers are used as the digitizers. The control devices are additional external devices developed to help control and automate the process of data acquisition: they comprise light intensity control USB boards to provide the correct amount of light to view the cells, touch panels for user-instrument interaction, and bar code readers to identify vials and experiments. The software, on the other hand, is a complex mosaic of different elements, each of which has a specific task to accomplish. These building blocks include the real-time acquisition, archiving, networking, processing, modelling, sensor output presentation and user interfaces. Our goal is to develop, integrate and optimize all these components to produce a viable and working device. The prototypes evolved from an offline, portable sensor equipped with a single high-resolution CCD camera and high-quality optics, to distributed online sensors with multiplexed CCD cameras and affordable optics. The acquisition board digitizes in real time the images from one to twelve multiplexed high resolution cameras. Several operational requirements must be met. First, a fault-tolerant and stable control over the input devices and control devices must be provided. Secondly, acquisition timing errors should be minimized as a trade-off between performance and the use of a low-cost, general-purpose, industry-standard operating system such as Microsoft Windows NT. Finally, in order to reduce development time and increase code reusability, a common abstraction layer is designed to provide for flexible use with various types of digitizers and cameras. As part of a distributed detection network, each sensor is able to exchange data with other "trusted" sensors and users, and to allow remote control of certain tasks. The sensor may be seen as a node capable of transmitting and receiving acquired or processed data to a distant device (another sensor, a workstation or a PDA) for visualization, inspection and decision-making by a front-end user. Each node on the network provides a set of complementary services including data acquisition, data processing, communication and system. The mandatory system service monitors the local system performance and manages data archiving. The communication service connects the various services on the network by enabling message-passing, file transfer and caching. The sensor network integrates a lightweight, interoperable and flexible RPC (Remote Procedure Call) protocol to achieve real-time control and monitoring of these distributed resources. A reliable embedded database system is used to store metadata bound to acquired and processed images. This database is also used to maintain information on neighbor nodes, and to check access credentials of available local services. Finally, by adding store-and-forward messaging capabilities, the application can be extended to work in wireless and mobile networks. / Graduation date: 2003

This thesis explores the feasibility of using melanophore-based biosensors from Oreochromis niloticus. Melanophores are one type of pigmented cell of the scales and fins of fish that respond in a motile fashion to a diverse range of stimuli. Fish scales were employed as the first step in determining the utility of melanophores as biosensors. Responsiveness of melanophores in scales was quantitated with several bioactive agents. Experiments with depolarizing potassium ion, guanethidine, yohimbine (an adrenergic antagonist), and capsaicin (a sensory stimulant) provided evidence that melanophores are under nervous regulation. Conditions were developed to allow simplification of intact scale preparations, entailing epidermal removal and dennervation of scales. This simplification resulted in increased sensitivity and responsiveness to a larger array of bioactive agents, including a cyclic AMP analog. The simplified preparation was successfully tested for its ability to function as a biosensor using pharmaceutical eye drops; the response observed was determined to be due to naphazoline, an adrenergic agonist. Methods were developed that enabled culturing of chromatophores independent from scales. Cultured chromatophores were found to be responsive to bioactive agents with a comparable degree of sensitivity as simplified scale preparations. Attempts were undertaken to develop co-cultures of chromatophores with other cell types and with further development melanophore-based biosensors can be exploited. / Graduation date: 1997

Thesis (M.S.)--Baylor University, 2005. / Includes bibliographical references (p. 53-56).

In the first part of this work, magnetized nanoporous silica based microparticles (MMPs) are used for horseradish peroxidase (HRP) immobilization and applied in amperometric peroxidase-based biosensors. A homemade magnetized carbon paste electrode permits the MMPs attraction close to the electrode surface. The resulting original biosensor is applied to the investigation of enzymatic oxidation of model drug compounds namely, clozapine (CLZ) and acetaminophen (APAP) by HRP in the presence of hydrogen peroxide. The biosensor operates at a low applied potential and the signal corresponds to the electro-reduction of electroactive species enzymatically generated. The biosensor allows performing the quantitation of the two drug compounds in the micromolar concentration range. It allows also the study of thiol compounds based on the inhibition of the biosensor response. Interestingly, distinct inhibition results are observed for HRP entrapped in the silica microparticles compared to the soluble HRP. We expect that this type of biosensors holds high promise in quantitative analysis and in biotransformation studies of drug compounds. In the second part of this thesis work, HRP immobilized magnetic nanoparticles are injected on-line and magnetically retained, as a microreactor, in the capillary of a CE setup. The purpose of such a configuration is to develop an analytical tool for studying “in vitro” drug biotransformation. The advantages expected are (i) minimum sample (drug compound) and biocomponent (enzyme) consumption, (ii) high analysis throughput, (iii) selectivity and sensitivity. In order to illustrate the potential of such an instrumental configuration, it has been applied to study acetaminophen as model drug compound. The mechanistic information obtained by the HRP/H2O2 system is in agreement with literature data on acetaminophen metabolization. Horseradish peroxidase kinetic studies are realized by this setup and the apparent Michaelis constant is determined. Capillary electrophoresis permitted the identification of APAP off-line biotransformed products such as N-acetyl-p-benzoquinone imine (NAPQI), the APAP dimer and APAP polymers as inferred from literature data. The formation of the APAP dimer was further confirmed by electrospray ionization mass spectrometry.

En aquesta tesis s'han realitzat diferents síntesis de nanopartícules com són els quantum dots i les nanopartícules d'or i d'argent amb els seus corresponents coreshells (Au-Ag i Ag-Au). Aquestes nanopartícules s'han caracteritzat per diferents tècniques tant òptiques com especialment les electroquímiques. S'ha realitzat un nou sistema de quantificació electroquímica dels quantum dots sintetitzats pel mètode arrested precipitation, utilitzant elèctrodes serigrafiats i un aparell de detecció portàtil.Aquests quatum dots han estat utilitzats en un sensors de DNA i amb detecció electroquímica de celules com a marca electroquímica, utilitzant la tècnica de detecció electroquímica directe que s'havia emprat en la determinació de quantum dots. / Different synthesis of nanoparticles was carried out in this thesis, such as cadmium sulphide quatum dots, gold nanoparticles, silver nanoparticles and core-shell nanoparticles (Au-Ag and Ag-Au). These nanoparticles were characterized by different techniques such as optical and especially electrochemical techniques. CdS-QDs (synthesized by arrested precipitation method) were quantified using an electrochemical direct detection method with screen-printed electrodes and a portable potentiostat.These CdS-QDs were used to label in DNA sensor of hybridization and also to detect HeLa cells using the electrochemical direct method that was used in CdS-QDs determination.