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Micro- and nano-electrodes have distinct advantages over large electrodes, including their decreased iR drop and enhanced mass transport due to radial diffusion characteristics which leads to the ready establishment of a steady state (or near steady-state) signal without convection. This enhanced mass transport also leads to increased current densities and signal to noise ratios. However, there is a need for fabrication techniques which reproducibly give micro- and nano-electrodes of controlled size and shape. The optimisation of systematic arrays on the nano-scale, open up possibilities for developing highly sensitive electrode devices, for use in physical chemistry and the determination of fast electrode kinetics and rates of reaction, as well as to provide highly sensitive electroanalytical devices, able to detect very low concentrations of substrates. This thesis first presents work involving the fabrication and characterisation on silicon substrates of square platinum microelectrodes. There is already an established theory for the behaviour of microdisc electrodes however, it is easier to make microsquares reproducibly using pixellated photomasks. The voltammetric and ac impedance characteristics of these electrodes in background electrolyte and in the presence of ferri/ferrocyanide redox couple are presented and the response is theoretically analysed. A combination of computer simulation, theory and experimentation show that these electrodes have increased current densities (14% greater) compared with a microdisc of equivalent radius and an alternative theoretical expression is presented to calculate the limiting current of microsquares at all dimensions. This thesis then discusses the development and optimisation of novel nano-band cavity array electrodes (CaviArE), using standard photo-microlithographic techniques. The resulting architecture encloses a Platinum nanoband of 50 nm width within each array element that is positioned half way up the vertical edges of shallow square cavities (depressions), with a total depth of 1050 nm. The width of the square cavity and the separation of the array elements can be controlled and systematically altered, with great accuracy. The CaviArE devices are shown to give quantitative pseudo-steady-state responses characteristic of multiple nanobands, whilst passing overall currents consistent with a macroelectrode. The array has a much enhanced signal-tonoise ratio compared with an equivalent microsquare array, as it has 0.167% of the area and is therefore markedly less affected by non-Faradaic currents, while it passes comparable Faradaic currents. At high sweep rates the response is also virtually unaffected by solution stirring. The impedammetric characteristics presented show different diffusional regimes at high, medium and low frequencies, associated with diffusion within individual square cavities, outside of the cavity and finally across the whole array as the diffusional fields of the neighbouring array elements overlap. Justification and fitting of equivalent circuits to these frequency regions provide details about the charge transfer, capacitance and diffusional processes occurring. The results show that these systems are highly sensitive to surface transfer effects and a rate constant for ferricyanide of 1.99 cm s-1 was observed, suggesting fast kinetic processes can be detected. Together, these characteristics make nanoband electrode arrays, with this architecture, of real interest for sensitive electroanalytical applications, and development of devices for industrial application is currently being undertaken.

In this thesis, a combination of density functional theory (DFT) based calculations and nonequilibrium Green’s functions are employed to investigate electron transport in molecular switches, molecular cords and nanoscale devices.   Molecular electronic devices have been proposed as an approach to complement today’s silicon based electronic devices. However, engineering of such miniature devices and design of functional molecular components still present significant challenges.   First, the way to connect a molecule to conductive electrodes has to be controlled. We study, in a nanoelectrode-nanoparticle platform, how structural changes affect the measured conductance and how current fluctuations due to these structural changes can be decreased. We find that, for reproducible measurements, it is important to have the molecules chemically bonded to the surfaces of adjacent nanoparticles. Furthermore, we show by a combination of DFT and theoretical modeling that we can identify signals from single-molecules in inelastic electron spectroscopy measurements on these devices.   Second, active elements based on molecules, some examples being switches, rectifiers or memory devices, have to be designed. We study molecular conductance switches that can be operated by light and/or temperature. By tuning the substituents on the molecules, we can optimize the shift of the most conducting molecular orbital and increase the effective coupling between the molecule and the electrodes when going from the OFF to the ON-state of the switches, giving high switching ratio (up to three orders of magnitude). We also study so called mechanoswitches that are activated by a mechanical force elongating the molecules, which means that these switches could operate as sensors.   Furthermore, we have studied two different classes of compounds that may function either as rigid molecular spacers with a well-defined conductance or as molecular cords. In both cases, we find that it is of great importance to match the conjugation of the anchoring groups with the molecular backbone for high conductance.   The last part of the thesis is devoted to another interesting semiconductor material, diamond. We have accurately calculated the band structure and effective masses for this material. Furthermore, these results have been used to calculate the Hall coefficient, the resistivity and the Seebeck coefficient.

Des réseaux aléatoires de nanoélectrodes ont été utilisés comme plateformes analytiques pour développer de nouveaux biocapteurs enzymatiques ou d’affinité. Dans ce travail de thèse, il s’est agi de préparer un biocapteur à glucose miniaturisé et des immunocapteurs électrochimiques et électrochimiluminescents (ECL) pour le diagnostic de la maladie de coeliaque. Dans un premier temps, un biocapteur enzymatique de seconde génération a été développé en exploitant les propriétés de réseaux aléatoires de nanoélectrodes. Ces réseaux ont été préparés par dépôt d’or au niveau de membranes "track-etched" de polycarbonate. Le capteur à glucose a été obtenu en immobilisant la glucose oxydase sur la surface de polycarbonate non-conductrice alors que les nanoélectrodes d’or sont exploitées comme transducteur. Le cation (ferrocènylmethyl)triméthylammonium a servi comme médiateur redox dans cette configuration expérimentale qui a conduit à une limite de détection de 36 μM pour le glucose.Dans un second temps, ce travail a porté sur l’élaboration d’outils de diagnostic pour la maladie de coeliaque. C’est une maladie auto-immune qui induit une concentration anormalement élevée de l’anticorps anti-transglutaminase (anti-tTg) dans le sang. Cette molécule anti-tTG est un biomarqueur adapté pour le diagnostic de cette pathologie. Les techniques de diagnostic actuelles souffrent d’une spécificité et d’une sensibilité insuffisantes. Pour améliorer ces aspects analytiques, deux types d’immunocapteurs ont été développés. Ils différent par la nature du signal, soit électrochimique soit ECL. La première étape commune est l’immobilisation, à la surface du polycarbonate entourant les nanoélectrodes, de la protéine tTG qui permet de capturer l’anticorps anti-tTg. Pour la détection électrochimique, un anticorps secondaire marqué par la peroxydase du raifort peut réagir avec un méditeur redox tel que l’hydroquinone et ainsi induire un signal électrochimique au niveau des nanoélectrodes. Pour le capteur ECL, la capture de l’anticorps cible anti-tTG permet de fixer ensuite un anticorps secondaire biotinylé qui se lie avec le luminophore, Ru(bpy)3+2, modifié par une streptavidine. L’imposition d’un potentiel suffisamment anodique au niveau des nanoélectrodes oxyde le co-réactif, la tri-n-propylamine, et génère ainsi des flux importants de radicaux qui diffusent et induisent l’émission ECL en réagissant avec le luminophore immobilisé. Cela conduit à une limite de détection de 0,5 ng.mL-1 qui est inférieure à celle obtenue par la voie électrochimique. Les 2 immunocapteurs ont été appliqués à l’analyse d’échantillons de sérum sanguins de patients et cela a permis de discriminer les échantillons des patients sains de ceux atteints de cette pathologie. / Nanoelectrode ensembles (NEES) are prepared, functionalized and tested to prepare enzymatic and affinity sensors suitable for advanced molecular diagnostics purposes, namely the development of a miniaturized glucose biosensor and the preparation of novel electrochemical and electrochemiluminescence immunosensors for celiac disease diagnostics.For the first goal, a second generation enzymatic microbiosensor was developed exploiting the properties of NEEs prepared by electroless gold deposition in track-etched polycarbonate (PC) membrane. The micro-NEE glucose biosensor (overall radius of 400 μm) was obtained by immobilizing glucose oxidase (GOx) on the nonconductive PC component of the NEE, while the Au nanoelectrodes were used exclusively as transducers. The (Ferrocenylmethyl)trimethylammonium cation (FA+) was used as the redox mediator. The proposed biosensor showed outstanding analytical performances with a detection limit of 36 μM for glucose.The second goal concerns celiac disease (CD) diagnostics. CD is an auto-immune disorder which reflects in abnormally high blood levels of the anti-tissue transglutaminase (anti-tTG) antibody, suitable as biomarker for CD diagnosis. Existing diagnostic techniques lack the desired level of sensitivity and specificity so that a confirmatory biopsy test is required. To overcome this limit, in this work electrochemical (EC) and electrogenerated chemiluminescence (ECL) immunosensors are proposed and studied. The two kinds of sensor employ the same biorecognition platform, based on tTG as biorecognition layer and NEEs as electrochemical transducers. EC and ECL sensors differ by the label used to develop the detection signal. By exploiting the high affinity of PC for proteins, the capture agent tTG is at first immobilized on the PC of the NEEs obtaining a tTG-NEEs which captures anti-tTG. For EC detection, the label is a secondary Ab labeled with horseradish peroxidase, using hydroquinone as redox mediator to generate the detection signal. For ECL, the sensor, after capturing anti-tTG, is reacted with a biotinylated secondary antibody to bind streptavidinatede Ru(bpy)3+2 luminophore. Application of an oxidizing potential in tripropylamine (TPrA) solution generates an intense ECL suitable for the sensitive ECL detection of anti-TG. Note that TPrA acts as redox mediator and ECL co-reactant. Both EC and ECL sensors are applied to human serum samples, showing to be suitable to discriminate between healthy and celiac patients. A comparison between the two approaches indicates that the lowest detection limit, namely 0.5 ng mL-1 of anti-TG, is achieved with the ECL immunosensor.

Verapamil is a commonly used medicine for the treatment of supraventricular arrhythmias, angina and hypertension. Recently, some newly developed applications of Verapamil, such as treating hypomania and chemotherapy for cancers, have been reported. Thus, monitoring the concentration of Verapamil accurately is very important. The major clinical analytical methods of Verapamil concentration determination are high performance liquid chromatography (HPLC) with UV or with fluorescence detector. However, these analytical methods have some disadvantages, like expensive instruments, complex operation, and time-consuming etc. The chemical structure and properties of Verapamil are very stable. The preliminary result of electrochemical analysis doesn¡¦t show any electrochemical activity. In this study, we developed an innovative ozone pre-treatment method to oxidize Verapamil to the smaller molecules and change its structure. Verapamil have excellent electrochemical activity after ozone pre-treatment. The spectroscopy and mass spectrometry show the changes of Verapamil structure. The products of Verapamil treated with ozone are also predicted by mass spectrometry. The gold nanoelectrode ensemble electrodes (GNEE) are used as working electrode for its good catalytic activity of electrochemical reaction, high sensitivity and high selectivity. The overall experimental framework of this study is microchip with GNEE working electrode accompanied by cyclic voltammetry, an electrochemical analytical instrument. Compared with traditional analytical methods, the system has some advantages such as small size, micro sample volume, easy operation, rapid detection and low cost. The limit concentration of Verapamil solution for stable detection in the system is 10 ng/mL. A linear dynamic range with a high correlation factor from 10 ng/mL to 100 £gg/mL was obtained. For the analysis of serum sample, Verapamil present excellent electrochemical activity at 1 ng/mL. A linear dynamic range with a high correlation factor from 1 ng/mL to 100 £gg/mLwas obtained. According to the results, our system for clinical Verapmil concentration analysis has the feasibility of the practical application.

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Determination of bio-material by using enzyme, fluorophore or metal-nanoparticles as markers is very important. Generally, gold-nanoparticles have been used frequently as marker for increasing the sensitivity in bio-chemical assay. In this research, gold-nanoparticles were used as marker for immunoassay, DNA sequence assay, and protein analysis. However, the size of gold-nanoparticles affects directly the results of electrochemical detection. For improving the sensitivity of electrochemical method, enlargement of gold-nanoparticles was used in this study. By electroless deposition, Au will be deposited on the surface of gold-nanoparticles. The electrochemical response will thus be increased substantially. In immunoassay and DNA sequence assay, traditional 96-wells microtiter plate was used for immobilizing antibody or oligonucleotide, and the gold-nanoparticles were marked subsequently base on the immunoreaction or protein reaction of streptavidin and biotin. After gold-nanoparticles were enlarged, they were dissolved and transferred to an electrochemical cell for square wave stripping voltammetry¡]SWSV¡^analysis. Under optimal experimental condition, dynamic range of 1 ~ 500 pg/mL and 0.52 ~ 1300 aM were found respectively for RIgG and Target DNA analysis, and a good linear relationship¡]R2 = 0.9975 and 0.9982¡^. The relative standard deviation¡]R.S.D.¡^ of blank were 2.8 % and 2.4 %¡]n = 11¡^for immunoassay and DNA assay, respectively. And the variance was 2.4 %¡]n = 9¡^and 2.4 %¡]n = 12¡^for immunoassay and DNA assay, respectively. The detection limit¡]based on S/N = 3¡^of RIgG and DNA were 0.25 pg/mL and 0.52 aM, respectively. They are very competitive compared with similar results reported in the literature. Additional, a gold nanoelectrode ensemble¡]GNEE¡^coupled microchip system was developed for bio-electrochemical analysis. Due to the difference in mobility of urea and urease were mixed and allowed the enzymatic reaction to proceed in microchannel. The enzymatic product NH4+ was determined by the coupled GNEE at the outlet of the channel. Another experiment of streptavidin conjugated gold-nanoparticles¡]streptavidin-Au¡^, reductant and gold-ion¡]Au3+¡^solution was be applied here, too. The product, NH4+ or Au3+ was passed through downstream of microchannel and detected by GNEE of electrochemical system. Satisfactory linear relationship¡]R2 = 0.9778 and 0.9657¡^were found from 0.1 mM to 50 mM for NH4+ and urea in the range of 0.02 mM to 5.0 mM, respectively. The other satisfactory linear relationship¡]R2 = 0.9842 and 0.9507¡^ were found between 3.75 mg/mL and 3.75 g/mL for Au3+ and streptavidin-Au in the range of 0.2 ng/mL to 100 ng/mL, respectively. Variances of 2.5 %¡]n = 6¡^was found for analysis of with the microchip system.

Doctor of Philosophy / Department of Chemistry / Jun Li / Developing new and rapid methods for pathogen detection with enhanced sensitivity and temporal resolution is critical for protecting general public health and implementing the food and water safety standards. In this research vertically aligned carbon nanofiber nanoelectrode arrays (VACNF NEAs) have been explored as a sample manipulation tool and coupled with fluorescence, surface enhanced Raman scattering (SERS) and impedance techniques for pathogen detection and identification. The key objective for employing a nanoelectrode array is that the nano-Dielectrophoresis (nano-DEP) at the tip of a carbon nanofiber (CNF) acts as a potential trap to capture pathogens. A microfluidic device was fabricated where nanofibers (~ 100 nm in diameter) were placed at the bottom of a fluidic channel to serve as a ‘point array’ while an indium tin oxide coated glass slide acted as a macroscale counter electrode. The electric field gradient was highly enhanced at the tips of the CNFs when an AC voltage was applied. The first study focused on the capture of the viral particles (Bacteriophage T4r) by employing a frequency of 10.0 kHz, a flow velocity of 0.73 mm/sec, and a voltage of 10.0 Vpp. A Lithenburg type of phenomenon was observed, that were drastically different from the isolated spots of bacteria captured on VACNF tips in previous study. At the lowest employed virus concentration (1 × 10[superscript]4 pfu/mL), a capture efficiency of 60% was observed with a fluorescence microscope. The motivation of the second study was to incorporate the SERS detection for specific pathogen identification. Gold-coated iron-oxide nanoovals labeled with Raman Tags (QSY 21), and antibodies that specifically bound with E.coli cells were utilized. The optimum capture was observed at a frequency of 100.0 kHz, a flow velocity of 0.40 mm/sec, and a voltage of 10.0 Vpp. The detection limit was ~210 CFU/mL for a portable Raman system with a capture time of 50 seconds. In the final study, a real-time impedance method was employed to detect Vaccinia virus (human virus) in the nano-DEP device at 1.0 kHz and 8.0 Vpp giving a detection limit of 2.51 × 10[superscript]3 pfu/mL.