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1
Brady, Charlotte Louise. "Development and characterisation of microelectrodes for extreme environments." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7852.
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Microelectrodes have been found to be a valuable tool in a variety of analytical studies. Their advantages over macro-sized electrodes are well known, including their enhanced mass transport properties (due to their ubiquitous hemispherical diffusion) which lead to steady state responses without external convection. They also exhibit high signal-to-noise ratios (greater sensitivities), furthering their analytical application. Microelectrode arrays are analytical devices with multiple electrodes. There are suitable for practical sensing with all the benefits of microelectrodes but with greater currents, leading to greater ease of measurement. To produce a reliable electroanalytical device the microelectrode response must be reproducible, a fundamental property based on the quality control of their production. Square microelectrode and array fabrication techniques have been developed for this purpose. This research discusses the fabrication and development of closely spaced arrays of square microelectrodes. Simulated and measured responses are compared and used to characterize electrode and array responses by cyclic voltammetry, electrical impedance spectroscopy and current-time transients. Measurements on variably spaced arrays allow insight into overlap of hemispherical diffusion from individual electrodes and the subsequent effect including peak current output on the array device. By studying these devices key insights into the mass transport properties of single square microelectrodes and microelectrode arrays were gained. This study also prepares and develops microelectrodes from materials appropriate for use in the extreme environments of molten salts and concentrated nitric acid solutions. These robust electrodes were developed for use in hydro- and pyro-chemical techniques for nuclear fuel reprocessing. These results demonstrate the practical uses for microelectrode systems across a wide range of chemical systems and in extreme conditions.
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Hodgson, Alexia Wilgith Elsa. "Microelectrodes in analysis." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243097.
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McNally, Michael. "Fabrication, characterisation and modification of a carbon film microelectrode to selectively monitor dopamine in vivo." Phd thesis, Electronic version, 2005. http://hdl.handle.net/1959.14/16067.
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Typescript.Thesis (PhD)--Macquarie University (Division of Environmental & Life Sciences, Dept. of Chemistry & Biomolecular Sciences), 2005.
Includes bibliographical references.
Microelectrode voltammetry -- Experimental -- Microelectrode fabrication -- Characterisation of the carbon film surface: Surface stability - X-ray photoelectron spectroscopy - Raman spectroscopy - Capacitance - Edge plane concentration - Potential window - Surface concentration of alkenes and alkynes - Outer sphere electron transfer using hexaamineruthenium (III) chloride - Reduction of potassium hexacyanoferrate (III) - Anodic oxidation: diol to dione; dopamine and ascorbic acid - Surface oxidation - Ferrocene in a non aqueous solvent -- Selectivity: Formation of carboxylic acid groups on a carbon film surface by ferrous II sulfate complex oxidation - Ethanol modified carbon film surface - Modification of carbon film microelectrode surface using aromatic amines - Modification of carbon film surfaces to form a dual functional ascorbic acid barrier -- In vivo anti fouling properties of surface modified carbon film microelectrodes -- Conclusion.
In this thesis a procedure is presented for the fabrication of a microelectrode to monitor the neurotransmitter dopamine in vivo. The microelectrodes are fabricated by in situ pyrolysis of acetylene under a nitrogen blanket onto a quartz capillary. The carbon film was then anodically oxidised in the presence of 2,4-dinitroaniline. These microelectrodes are stable, provide the physical strength to penetrate brain tissue, have a low capacitance, are resistant to fouling in vivo and selectively suppress the endogenous ascorbic acid which oxidises at the same potential as dopamine. With such properties the carbon film microelectrode appears ideally suited for fast scanning cyclic voltammetric studies of cationic neurotransmitters such as dopamine in vivo.
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Blair, Ewen O. "The optimisation and characterisation of durable microelectrodes for electroanalysis in molten salt." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25671.
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This work presents microfabricated microelectrodes, capable of quantitative analysis in molten salt (MS). MSs are an electrolytic medium of growing interest, especially in the area of nuclear reprocessing. However, designing sensors for a MS-based nuclear reprocessing system is a challenge, owing to the usually corrosive nature and high operating temperatures (typically 450 - 500◦C) of MS. Microelectrodes are well placed as sensors, with numerous advantages over macro-scale electrodes. As a consequence, there have been previous attempts to utilise microelectrodes inMS. However, these have not been successful and all have suffered disadvantages inherent in traditional microelectrode manufacturing. The microelectrodes presented in this work were produced using standard microfabrication techniques and characterised in MS. An analysis of failure mechanisms guided a systematic study of material combinations. This resulted in a sensor, which is capable of delivering quantifiable electrochemistry in MS. However, the lifetime and yield of the sensor were determined to only be 46% and 1.4 hours respectively. Further investigation of the microelectrode failure mechanisms guided several layout changes to the microelectrode design. By reducing critical area, where defects or pinholes could form, these resulted in improvements in performance. This increased the yield to 65%, while the average lifetime increased up to 45 hours. Test structures were designed to investigate the causes of the continued microelectrode failures and identified shorting between the electrode metal and silicon substrate. This suggests the existence of defects in the underlying insulator are the cause of the 35% of microelectrodes which never functioned. Separate test structures suggested the lifetimes of the microelectrodes could also be improved by removing the need for a metal adhesion layer. Tantalum has been suggested as a replacement electrode metal and a proof of concept study demonstrated the feasibility of employing thin film tantalum as an electrode metal in LKE. Using this technology as a platform, several proof-of-concept microelectrode designs are also presented: liquid microelectrodes, microelectrode arrays, and a nanoelectrode. These are targeted at specific sensing applications, and provide an expanded spectrum of measurements in MS.
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Amphlett, Jonathan Lee. "Numerical simulation of microelectrodes." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341628.
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Perry, Samuel C. "Transient studies at microelectrodes." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/387227/.
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Transient studies of electrochemical systems at microelectrodes allow analysis under rapid mass transport conditions. The small active area allows rapid resolution of charging currents, giving access to meaningful information even at short times. Sampled current voltammetry at microelectrodes (MSCV) is a multistep technique whereby data is collected from a series of potential step experiments along the redox wave of interest. Varying the sampling time allows comparison of how a reaction proceeds at varying timescales, whilst simultaneously showing the potential dependence. Selection of an appropriate sampling time tunes the rate of mass transport to give quasireversible conditions, allowing facile kinetic analysis using quasireversible models. Application to the oxygen reduction reaction (ORR) revealed unreasonably large currents at short times. This work suggests that pre-adsorbed oxygen at the electrode surface is responsible. The presence of the pre-adsorbed oxygen was confirmed by its direct reduction in argon purged solution, and its strong dependence on the metal substrate. The resultant peak potentials were used to calculate the binding energies of varying metals towards oxygen (ΔG₀), which are in excellent agreement with the literature. This is useful, as ΔG₀ is a popular descriptor for oxygen reduction activity. Once the pre-adsorbed oxygen is consumed, MSCVs for the ORR can be used for standard kinetic analysis using Tafel or Koutecky-Levich analyses, with the advantage of the electrode being oxide free before each data point is recorded.
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Tait, Russell John, and mikewood@deakin edu au. "Development and application of a microelectrode based scanning voltammetric detector." Deakin University. School of Physical and Chemical Sciences, 1991. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20060720.100447.
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A large part of the work presented in this thesis describes the development and use of a novel electrochemical detector designed to allow the electrochemical characterisation of compounds in flowing solution by means of cyclic voltammetry. The detector was microprocessor controlled, which provides digital generation of the potential waveform and collection of data for subsequent analysis. Microdisk working electrodes are employed to permit both thermodynamic and kinetically controlled processes to be studied under steady-state conditions in flowing solutions without the distortion or hysteresis normally encountered with larger sized electrodes. The effect of electrode size, potential scan rate, and solution flow rate are studied extensively with the oxidation of ferrocene used as an example of a thermodynamically controlled process and a series of catecholamines as examples of a kinetically controlled process. The performance of the detector was best demonstrated when used as a HPLC post-column detector. The 3-dimensional chromatovoltammograms obtained allow on-line characterisation of each fraction as it elutes from the column.
The rest of the work presented in this thesis involves the study of the oxidative degradation pathway of dithranol. The oxidative pathway was shown to involve a complex free radical mechanism, dependent on the presence of both oxygen and, in particular light. The pathway is further complicated by the fact that dithranol may exist in either a keto or enol form, the enol being most susceptible to oxidation. A likely mechanism is proposed from studies performed with cyclic voltammetry and controlled potential electrolysis, then defined by subsequent kinetic studies.
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Silva, Eduardo Luís Trindade da. "Diamond microelectrodes for corrosion studies." Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14495.
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Doutoramento em Ciência e Engenharia de MateriaisEste trabalho teve como objetivos a produção, caracterização e aplicação de microelétrodos (MEs) de diamante como sensores amperométricos e potenciométricos em sistemas de corrosão nos quais a agressividade do meio e a presença de produtos de corrosão, constituem obstáculos que podem diminuir o desempenho, ou inviabilizar a utilização, de outros tipos de sensores. Os microeléctrodos são baseados em filmes finos de diamante dopado com boro (BDD – Boron Doped Diamond) depositados sobre fios de tungsténio afiados, através do método de deposição química a partir da fase vapor, assistida por filamento quente (HFCVD – Hot Filament Chemical Vapor Deposition). A otimização das diversas etapas de fabricação dos MEs deu origem ao desenvolvimento de um novo sistema de afiamento eletroquímico para obtenção destes fios e a várias opções para a obtenção dos filmes de diamante condutor e seu isolamento com resinas para exposição apenas da ponta cilíndrica. A qualidade cristalina dos filmes de diamante foi avaliada por espectroscopia de Raman. Esta informação foi complementada com uma caracterização microestrutural dos filmes de diamante por microscopia eletrónica de varrimento (SEM), em que se fez a identificação da tipologia dos cristais como pertencendo às gamas de diamante nanocristalino ou microcristalino. Os filmes de BDD foram utilizados na sua forma não modificada, com terminações em hidrogénio e também com modificação da superfície através de tratamentos de plasma RF de CF4 e O2 indutores de terminações C-F no primeiro caso e de grupos C=O, C-O-C e C-OH no segundo, tal como determinado por XPS. A caracterização eletroquímica dos MEs não modificados revelou uma resposta voltamétrica com elevada razão sinal/ruído e baixa corrente capacitiva, numa gama de polarização quasi-ideal com extensão de 3 V a 4 V, dependente dos parâmetros de crescimento e pós-tratamentos de superfície. Estudou-se a reversibilidade de algumas reações heterogéneas com os pares redox Fe(CN)6 3-/4- e FcOH0/+ e verificou-se que a constante cinética, k0, é mais elevada em elétrodos com terminações em hidrogénio, nos quais não se procedeu a qualquer modificação da superfície. Estes MEs não modificados foram também testados na deteção de Zn2+ onde se observou, por voltametria cíclica, que a detecção da redução deste ião é linear numa escala log-log na gama de 10-5-10-2 M em 5 mM NaCl. Realizaram-se também estudos em sistemas de corrosão modelares, em que os microeléctrodos foram usados como sensores amperométricos para mapear a distribuição de oxigénio e Zn2+ sobre um par galvânico Zn-Fe, com recurso a um sistema SVET (Scanning Vibrating Electrode Technique). Foi possível detetar, com resolução lateral de 100 μm, um decréscimo da concentração de O2 junto a ambos os metais e produção de catiões de zinco no ânodo. Contudo verificou-se uma significativa deposição de zinco metálico na superfície dos ME utilizados. Os MEs com superfície modificada por plasma de CF4 foram testados como sensores de oxigénio dissolvido. A calibração dos microeléctrodos foi efetuada simultaneamente por voltametria cíclica e medição óptica através de um sensor de oxigénio comercial. Determinou-se uma sensibilidade de ~0.1422 nA/μM, com um limite de deteção de 0.63 μM. Os MEs modificados com CF4 foram também testados como sensores amperométricos com os quais se observou sensibilidade ao oxigénio dissolvido em solução, tendo sido igualmente utilizados durante a corrosão galvânica de pares Zn-Fe. Em alguns casos foi conseguida sensibilidade ao ião Zn2+ sem que o efeito da contaminação superficial com zinco metálico se fizesse sentir. Os microeléctrodos tratados em plasma de CF4 permitem uma boa deteção da distribuição de oxigénio, exibindo uma resposta mais rápida que os não tratados além de maior estabilidade de medição e durabilidade. Nos MEs em que a superfície foi modificada com plasma de O2 foi possível detetar, por cronopotenciometria a corrente nula, uma sensibilidade ao pH de ~51 mV/pH numa gama de pH 2 a pH 12. Este comportamento foi associado à contribuição determinante de grupos C-O e C=O, observados por XPS com uma razão O/C de 0,16. Estes MEs foram igualmente testados durante a corrosão galvânica do par Zn-Fe onde foi possível mapear a distribuição de pH associada ao desenvolvimento de regiões alcalinas causadas pela redução do oxigénio, acima da região catódica, e de regiões ácidas decorrentes da dissolução anódica do ânodo de zinco. Com o par galvânico imerso em 50 mM NaCl registou-se uma variação de pH aproximadamente entre 4,8 acima do ânodo de zinco a 9,3 sobre o cátodo de ferro. A utilização pioneira destes MEs como sensores de pH é uma alternativa promissora aos elétrodos baseados em membranas seletivas.
This work was dedicated to the production, characterization and application of diamond microelectrodes (MEs) in corrosion systems as amperometric and potentiometric sensors in which the aggressive media and the presence of corrosion products can affect the performance, or even impede the use of other types of sensors. The MEs are based in boron doped diamond (BDD) thin films grown by HFCVD (Hot Filament Chemical Vapor Deposition) on top of sharp tungsten filaments. The optimization of the various ME fabrication steps gave origin to a novel electrochemical etching technique for the production of sharp metal wires and to multiple options for the growth of diamond films and their insulation with resins in order to expose only the cylindrical tip. The crystalline quality of the diamond films was evaluated with Raman spectroscopy. Complementary microstructural information was gathered by scanning electron microscopy (SEM), to identify the microcrystalline or nanocrystalline nature of the diamond coatings. The BDD films were used in the as-grown form, with hydrogen terminated surface and also with surface modification, by RF-plasma, using CF4 and O2 for inducing different surface terminations, C-F bonds in the first case and C=O, CO- C and C-OH in the second, as detected by XPS. The electrochemical characterization of the MEs revealed a voltammetric response with high signal-to-noise ratio and low capacitive current. The potential range of water stability varied from 3 V to 4V, depending on the growth parameters and surface treatments. Heterogeneous electron transfer kinetics were measured using the Fe(CN)6 3-/4- and FcOH0/+ redox couples and it was verified that the kinetic constant, k0, is higher for the as-grown MEs than for the modified ones. The as-grown MEs were used for the detection of Zn2+ exhibiting a log-log linear response in the range of 10-5-10-2 M in 5 mM NaCl, by cyclic voltammetry. Studies in model corrosion systems were also performed in which the MEs were used as amperometric sensors to map the distribution of oxygen and Zn2+ above a corroding galvanic Zn-Fe couple, by using a SVET (Scanning Vibrating Electrode Technique) system. It was possible to detect with a lateral resolution of 100 μm, a decrease in O2 concentration above both metals and the release of zinc cations above the anode. However, a significant zinc deposition at the surface of the electrodes was observed. The MEs modified by CF4 plasma were tested as dissolved oxygen sensors. The calibration of the microelectrodes was performed simultaneously by cyclic voltammetry and optical measurement with a commercial oxygen sensor. A sensitivity of ~0.1422 nA/μM was determined, with a detection limit of 0.63 μM. The fluorinated MEs were also tested during galvanic corrosion of Zn-Fe couples. In some cases sensitiveness to Zn2+ was also achieved without zinc contamination. The CF4 plasma treated MEs allow a good oxygen mapping, showing a faster response than the as-grown MEs, as well as higher measurement stability and longer lifetime. For the O2 plasma treated MEs it was possible to detect, by zero-current chronopotentiometry, a pH sensitivity of ~51 mV/pH in a pH 2 to pH 12 range. This behavior was attributed to the contribution of the C-O and C=O groups, observed by XPS with an O/C ratio of 0.16. These MEs were also tested during the galvanic corrosion of a Zn-Fe couple where it was possible to map the pH distribution deriving from the development of alkaline regions caused by oxygen reduction, above the cathode, and of acidic regions resulting from the anodic dissolution of zinc. With the galvanic couple immersed in 50 mM NaCl a pH variation was registered from ca. 4.8 above the zinc anode to 9.3 above the cathode. The innovative use of these MEs as pH sensors is a promising alternative to the selective membrane based MEs.
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Saillard, Audric. "Mercury Amalgam Electrodeposition on Metal Microelectrodes." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7193.
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Mercury amalgam microelectrodes, typically fabricated by electrodeposition of mercury onto metal (platinum, gold, silver) inlaid disks, possess certain advantageous properties for scanning electrochemical microscopy (SECM) and electroanalysis. But as applications require more and more precision, fundamental questions concerning the exact shape and constitution of the amalgam can become important for interpreting SECM experimental data. The purpose of this study is to analyze in depth the formation of the amalgam, in order to provide a better understanding of the key physical processes, and so be able to judge of the accuracy of the currently used models and refine them when necessary.
The amalgam formation is the result of several processes that occur roughly at two different scales: the global scale, which is microscopic, and the local scale, of the order of few nanometers. On the global scale, the dominant physical process is the mass transport, driven almost entirely by diffusion, which determines the rate of mercury deposition. Other phenomena occur at the smaller local scale. Their understanding is essential to predict precisely the volume and shape of the amalgam at shorter times. Among these local phenomena, nucleation and droplet interactions appear critical. The former sets the formation rate and the size of the isolated mercury droplets that are initially formed at the surface of the electrode. An understanding of the latter is necessary to determine the droplet coalescence process.
Among the specific accomplishments of this Master thesis work, a time scale analysis of the global phenomena has been performed leading to the conclusion that quasi-steady state diffusion of mercury ions in the bulk mainly defines the electrodeposition rate. Then, a series of analytical formulations for diffusion-limited electrodeposition current available in the literature has been quickly analyzed, leading to development of analytical/numerical models. These latter have been implemented, and results were critically compared with experimental data, leading to the conclusion that the early electrodeposition was not enough finely modeled. Mercury droplets nucleation and surface interaction have been identified as relevant processes of this period. They have next been investigated in detail, leading to the characterization of the nucleation process, and the derivation of two complimentary approaches on charged droplet stability. Regime maps have been developed, providing first explanations and quantitative information on charged droplet stability dependence on potential applied, electrolyte and droplet size. Finally, through analysis of theoretical predictions, a series of electroanalytical experiments have been proposed for the future validation of the suggested theoretical models.
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Caruana, Daren Joseph. "Electrochemical immobilisation of enzymes on microelectrodes." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240238.
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Martinez-Bonastre, Alejandro. "Poly(aniline) microelectrodes for ascorbate measurements." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442858.
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Leonhardt, Kelly. "Modelling of electrochemical processes at microelectrodes." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/344287/.
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In this work, the finite element modelling of 2D and 3D scanning electrochemical microsopy (SECM) systems is presented. The main focus has been on the influence of tip geometry and the presence of defects on the limiting current of the SECM tip. The geometry of the electrode of particular interest is conical with conical insulation, as this is the shape of AFM-SECM probes fabricated by our coworkers. This thesis presents an extensive study of the electrochemical response of conical electrodes both in the bulk solution and close to a surface. Key equations were derived for conical electrodes and a thorough quantitative analysis of the influence of the tip geometry, be it the parameters describing it or the presence of defects, is reported. A novel equation was derived to calculate the current in the bulk at a conical electrode with conical insulation and an extensive study of possible defects was conducted to allow users to adjust the expression and obtain a more accurate estimation of the limiting current. The spatial resolution defined as the ability of an electroactive probe to detect a conducting region of a given size- and the lateral resolution -the distance necessary to fully resolve a conducting region form an inert region- were both investigated for a range of geometries as well as for a selection of defects. This enables us to draw conclusions on the ideal tip, and how sensitive it would be to features of the substrate. A set of equations was derived to describe positive and negative feedback approach curves for cones, and steps were defined for users to determine the shape of the electrode from experimental approach curves. Simulated curves are also provided to help with the extraction of kinetics at the substrate surface from the experimental approach curves. Finally, the influence of a ring disc tip geometry was evaluated by monitoring the collection efficiency as a function of tip-substrate distance for different disc-ring separations.
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Palencsár, Iozsef Attila. "Single particle microelectrodes and microbatteries fundamental studies /." online version, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1144340892.
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Rudolph, Douglas Alexander. "Scanning Electrochemical Microscopy (SECM) with Amalgam Microelectrodes." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7133.
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This thesis focuses on in-situ studies at the solid-liquid interface by combining scanning electrochemical microscopy (SECM) with gold and platinum mercury amalgam microelectrodes. It is shown that stripping voltammetry experiments at imaging amalgam microelectrodes provide laterally resolved insight on the electrochemistry of biogeochemically relevant processes. SECM provides information on electroactive surface processes with high spatial resolution, and offers the opportunity to study heterogeneous electron-transfer reactions. Thereby, chemical species of interest, such as metal ions, can be electrochemically detected at mercury amalgam electrodes.
Platinum and gold mercury amalgam microelectrodes were developed for the detection of biogeochemically relevant analytes such as manganese and iron during SECM imaging experiments at the mineral/water interface establishing the fundamental basis of SECM imaging with amalgam microelectrodes.
SECM experiments were performed for the quantitative determination of Mn2+ during the dissolution of microstructured manganese carbonate (rhodochrosite) precipitates at mildly acidic conditions. SECM images along with spatially resolved quantitative data on the Mn2+ concentration were obtained.
This measurement concept was then extended to the investigation of the corrosion behavior of diamond-like carbon (DLC) protected zinc selenide (ZnSe) waveguides applied in mid-infrared attenuated total reflectance spectroscopy at strongly oxidizing conditions. The corrosion behavior of DLC coated and uncoated ZnSe crystals was studied obtaining laterally resolved information on the oxidative degradation of ZnSe at defects of the DLC layer utilizing SECM in combination with square wave anodic stripping voltammetry (SWASV) at gold amalgam microelectrodes. Thereby, insight on the corrosion behavior of ZnSe and concentration profiles of Zn2+ at oxidizing conditions was obtained. These results corroborate the utility of SECM imaging with amalgam microelectrodes for addressing relevant analytical questions.
Finally, the developed amalgam microelectrodes were applied for SECM studies of iron-reducing proteins separated from Shewanella microbes in native polyacrylamide gels. After calibration of Pt/Hg microelectrodes in bulk solution for the targeted analytes (iron and sulfur species), SECM approach curves recorded above the native gel enabled positioning of the amalgam electrode in close proximity above protein bands with suspected iron-reducing activity. This technique enabled the (semi)quantitative determination of the anaerobic respiratory activity associated with microbial proteins/protein complexes responsible for the reductive dissolution of manganese and iron oxides above microbial protein bands separated in a native gel matrix.
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Goodwin, Stefan. "Fabrication and measurement of graphene electrochemical microelectrodes." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/fabrication-and-measurement-of-graphene-electrochemical-microelectrodes(68041aff-f4b6-4562-b807-dd547ef9c002).html.
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The electrochemical properties of graphene were investigated using a novel and clean method to fabricate device structures with mechanically exfoliated graphene samples. Graphene is known as being particularly sensitive to both contaminating fabrication methods and the substrate it is placed on, with these effects being detrimental to accurate research into the fundamental properties and sensing applications of graphene. This thesis presents micron scale graphene electrodes that have not been subject to polymer contamination or micro-lithography methods. The effect of utilising atomically flat hexagonal boron nitride as a substrate material was investigated, believed to be the first example of this for graphene electrochemical measurements. Cyclic voltammetry demonstrated the expected steady-state behaviour for microelectrodes in the hemispherical diffusion regime. The reduction of IrCl62- in weak KCl electrolytes was studied to investigate the electron transfer characteristics of the graphene devices and the reproducibility of the measurements. Average values of the standard rate constant, k0 and the transfer coefficient, alpha were found to be 3.04 ± 0.78 ×10-3 cms-1 and 0.272 ± 0.024 respectively. These values differ significantly from previous similar studies, with the effect of reduced charge doping from the substrate and the potential dependence of the density of electronic states thought to account for the differences. Despite the clean fabrication methods, a relatively large variation between separate devices was found, highlighting an inherent variation in the properties of graphene samples.
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Mahon, Peter John, and mikewood@deakin edu au. "The determination of rate constants using microelectrodes." Deakin University. School of Science, 1992. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20050728.090033.
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An understanding of the rate and the mechanism of reaction is of fundamental importance in the many facets of chemistry. Electrochemical systems are further complicated by the heterogeneous boundary, between the solution and the electrode, that the electron passes through before any electrochemical reaction can take place.
This thesis concerns the development of methods for analysing electrode kinetics. One part involves the further development of the Global Analysis procedure to include electrodes with a spherical geometry which are traditionally the most popular form of electrodes. Simulated data is analysed to ascertain the accuracy of the procedure and then the known artifacts of uncompensated solution resistance and charging current are added to the simulated data so that the effects can be observed. The experimental analysis of 2-methyl-2-nitropropane is undertaken and comparisons are made with the Marcus-Hush electrochemical theories concerning electrode kinetics.
A related section explores procedures for the kinetic analysis of steady state voltammetric data obtained at microdisc electrodes. A method is proposed under the name of Normalised Steady State Voltammetry and is tested using data obtained from a Fast Quasi-Explicit Finite Difference simulation of diffusion to a microdisc electrode.
In a second area of work using microelectrodes, the electrochemical behaviour of compounds of the general formula M(CO)3(η3 - P2P1) where M is either Cr, Mo or W and P2P' is bis(2-diphenylphosphinoethyl)phenylphosphine) is elucidated. The development of instrumentation and mathematical procedures relevant to the measurement and quantitation of these systems is also investigated. The tungsten compound represents the first examples where the 17-electronfac+ and mer+ isomers are of comparable stability.
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Psalti, Ioanna S. M. "Microelectrodes : single and arrays in electron transfer." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302826.
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Sotiropoulos, Sotirios. "The cathodic reduction of oxygen at microelectrodes." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240817.
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Al-Shandoudi, Laila. "Transient studies of oxygen reduction at microelectrodes." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/380893/.
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Our group has previously reported the successful development of a steady state microelectrode sensor for the determination of dissolved oxygen concentrations in sea water. The work presented here underpins the development of a fast oxygen sensor for oceanographic applications; the overall aim is to determine the best conditions to measure dissolved oxygen concentrations with microdiscs on a time scale ranging from sub milliseconds to seconds. Previous studies with rotating disc and microelectrodes have shown how the apparent number of electrons, napp, varies between 4 and 2 as the steady mass transfer coefficient increases. The present study also aims to provide insight into the oxygen reduction reaction (ORR) and in particular to probe whether and how napp, depends on the time scale of the reaction. This thesis will describe the results of transient amperometric experiments recorded with microdisc electrodes. The experiments were carried out with different size Pt microdisc electrodes, using fast scan cyclic voltammetry, chronoamperometry and sampled current voltammetry. Model experiments were first conducted with ferrocene, FeCp2, in acetonitrile to validate the experimental approach. Subsequent model experiments were conducted with hexaammineruthenium (III) chloride, Ru(NH3)6Cl3, in aqueous chloride solutions. The ORR was also probed in aqueous chloride solutions. Experiments were also systematically conducted in absence of redox couple to investigate the role of background processes in determining the overall amperometric response over the different time scales considered. Where possible, fast scan voltammograms, chronoamperograms and sampled current voltammograms were compared to theoretical expressions or simulations. The work will also describe attempts to develop a potentiostatic conditioning waveform capable of pre treating the microdisc electrode in order to produce reliable oxygen reduction chronoamperograms. Various coatings were used for simultaneous determination of dopamine and oxygen species for biological application. The conditioning waveform at bare electrode was found to give more reproducible ORR amperometric response than the coatings alone.
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Palencsar, Iozsef Attila. "SINGLE PARTICLE MICROELECTRODES AND MICROBATTERIES: FUNDAMENTAL STUDIES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1144340892.
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Schuette, Sheila A. "Trace voltammetry using microelectrodes and modulation techniques /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu14873257407203.
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Thompson, Heather. "The influence of electrolyte on electrode processes and homogeneous chemical reactions." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263473.
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Farrington, Amiel Marjorie. "Practical microelectrodes produced by the Taylor wire process." Thesis, Birkbeck (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339191.
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Harrington, Michael Smith. "New analytical strategies for gold interdigitated filar microelectrodes /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487676847116274.
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Schwartz, Jacob C. "Functional and Categorical Analysis of Waveshapes Recorded on Microelectrode Arrays." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc4746/.
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Dissociated neuronal cell cultures grown on substrate integrated microelectrode arrays (MEAs) generate spontaneous activity that can be recorded for up to several weeks. The signature wave shapes from extracellular recording of neuronal activity display a great variety of shapes with triphasic signals predominating. I characterized extracellular recordings from over 600 neuronal signals. I have preformed a categorical study by dividing wave shapes into two major classes: (type 1) signals in which the large positive peak follows the negative spike, and (type 2) signals in which the large positive peak precedes the negative spike. The former are hypothesized to be active signal propagation that can occur in the axon and possibly in soma or dendrites. The latter are hypothesized to be passive which is generally secluded to soma or dendrites. In order to verify these hypotheses, I pharmacologically targeted ion channels with tetrodotoxin (TTX), tetraethylammonium (TEA), 4-aminopyridine (4-AP), and monensin.
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Kitzmiller, Joseph Paul. "Design, engineering,and evaluation of a novel microgrid electrode array to monitor the electrical activity on the surface of the cerebral cortex." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1084824069.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xiv, 82 p.; also includes graphics. Includes bibliographical references (p. 80-82). Available online via OhioLINK's ETD Center
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Selvakumaran, Jamunanithy. "Assessment of materials for use in chronically implantable microelectrodes." Thesis, University of Surrey, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273190.
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Mpholo, Moeketsi Isaac. "Electroosmotic pumping of fluids using asymmetric pairs of microelectrodes." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616030.
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Alshadokhi, Mohammed. "Design and characterisation of nanostructured microelectrodes for biomedical applications." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/375029/.
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The aim of the project is to create a nanostructured microelectrode pH sensor to measure the pH of brain fluids. This work will describe the fabrication, characterization and development of the nanostructured Pd electrodes and their assessment for use as pH sensors in the brain fluid. The palladium hydride α+β transition is located between the α and β phases where H/Pd atomic ratios range between 0.02 and 0.6. This region was selected to fabricate the pH sensor because its potential (Epd-H) is stable and independent of the hydrogen– palladium composition. In addition, Epd-H follows a linear relationship with pH. A nanostructured Pd film was chosen to fabricate the pH sensor in order to obtain a large electroactive area because Epd-H is not stable with microelectrode; a large area is needed to reach the equilibrium between palladium and hydrogen. Also, neurobiological pH measurements require a small sensor as a result of the limited biological sample quantities available. The nanostructured pH sensor H1-e Pd was made by liquid crystal templating method (LCT). Scanning electron microscopy (SEM) and electrochemical characterisation were used to estimate the radius a and electroactive area of the nanostructured Pd film after the deposition process. The α+β transition was prepared by loading hydrogen electrochemically before the experiments were carried out. The nanostructured Pd hydride electrode was then used to estimate the pH in different solutions including artificial cerebral spinal fluid (aCSF) and real brain fluid. The results obtained demonstrate the applicability of such electrodes to function as pH sensors in brain fluid. The biomedical applications requires high efficiency that can be affected by the biological samples contaminations onto the electrode. Thus, attempts were made to develop the H1-e Pd pH sensors performance by covering their surface with coats to stop the biological impurities.
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West, Richard H. "Double Pulse Coulometry for Interfacial Biosensing at Platinum Microelectrodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1344251678.
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Dorflinger, Charles. "CHARACTERIZATION OF CARBON FIBER MICROELECTRODES DECORATED WITH PLATINUM NANOPARTICLES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396887958.
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Bitziou, Eleni. "Development and applications of microelectrodes in hydrodynamic and photoelectrochemical systems." Thesis, University of Warwick, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441692.
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Lecomte, Aziliz. "Conception and characterization of flexible microelectrodes for implantable neuroprosthetic development." Thesis, Toulouse, INSA, 2016. http://www.theses.fr/2016ISAT0029/document.
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Les Interfaces Cerveau-Machine assurent une connexion bidirectionnelle entre un patient et son environnement. Un patient atteint de déficience motrice lourde peut, au moyen d'un dispositif implanté dans son cerveau, commander des objets connectés par la seule action de son activité cérébrale. Une des premières exigences que cela requiert est de concevoir un implant, dit neuroprothèse, susceptible de rester implanté de façon chronique. L’utilisation des micro-nano-technologies permet de fabriquer une neuroprothèse qui réponde aux exigences d’un tel dispositif : performant, fiable et limitant la réaction de rejet par l’organisme. Pour cela, l’implant est conçu sur un substrat flexible à base de polymère biocompatible. La souplesse de l’implant lui permet de mieux s’adapter aux tissus cérébraux et d’assurer un contact intime avec les neurones en diminuant la réaction inflammatoire. Cet implant est inséré au moyen d’un support rigide biodégradable issu de la fibroïne de soie. Des premiers tests sur culture in vitro et sur petit animal (souris) ont montré des résultats prometteurs en termes de biocompatibilité et biostabilité sur le court et moyen termeBrain-Computer Interfaces ensure a bidirectional connection between a patient and his environment. Using an implant in his brain, a patient suffering from severe motor deficiency can control external devices through the sole action of his cerebral activity. One of the major requirements for such application is to conceive an implant, also called neuroprosthesis, that is able to be implanted for long periods of time.Micro-nano-technology enable the fabrication of a neuroprosthesis that gives in the demands of such item: efficient, reliable and limiting body rejection mechanisms. To that aim, the implant is designed on a flexible substrate provided by a biocompatible polymer. Implant flexibility allows for better compliance with the brain tissues and insures a more intimate contact with the neurons while maintaining minimal inflammation. This implant is inserted in the brain using a bioresorbable support made of silk fibroin. First tests in vitro on culture cells, and in vivo on mice showed promising results in terms of biocompatibility and biostability in the short and medium term
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Angathevar, Veluchamy Raaja Raajan. "Structure and activity of Pseudomonas aeruginosa PAO1 biofilms." Thesis, Montana State University, 2006. http://etd.lib.montana.edu/etd/2006/angathevarveluchamy/AngathevarVeluchamyR0506.pdf.
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Toma-Daşu, Iuliana. "Theoretical modelling of tumour oxygenation and influences on treatment outcome /." Umeå : Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-262.
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Summerour, Jamie Maddox. "Tritium doped polyaniline as a β-irradiation source." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/26962.
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McNaughtan, Arthur. "The investigation of diagnostic and analytical microelectrode sensor measurement systems and strategies." Thesis, Glasgow Caledonian University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388933.
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Delaplace, Christine. "Electrochemical investigation of transient bubble phenomena." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313215.
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Abdelsalam, Mamdouh Elsayed. "Development of microelectrode techniques for analytical and environmental applications." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326794.
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Silva-Martinez, Susana. "Applications of ultrasound in electrochemistry." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242670.
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Sörensen, Sören Per. "Development of a cell-based drug screening platform : extracellular recording and electrochemical impedance spectroscopy on microelectrode array chips." Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486476.
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Two established methods, Electrochemical Impedance Spectroscopy (EIS) and extracellular recording, were implemented into a technology platform for non-invasive whole-cell biosensing. Electrical activity of cardiomyocytes and cell-substrate interaction of human ovarian cancer cells was monitored on electrode array chips. The performance of cells inside a microfluidic or closed low volume environment was investigated. Prior to the development of the entire microfluidic platform the two transducing methods were evaluated in single experiments. Processes as cellular attachment and detachment were monitored using EIS and single frequency impedance sensing. Electrodes of different size and structure were employed and compared for their impedance response. It was shown that small electrodes (A = 9·10-6 cm²) are more sensitive to cell-substrate interaction than larger ones (A = 9·10-5 cm²) and that the frequency used for analysis has a profound influence on the sensitivity. Data were modelled using a common equivalent circuit that represents a cell layer on an electrode resulting in an increase of the impedance magnitude by <170 % due to cell attachment. In order to demonstrate the potential of this method for biomedical applications, experiments related to anti-cancer strategies were performed. Cell detachment was induced by addition of synthetic integrin ligands and by hypericin mediated photodynamic therapy and monitored with impedance-based biosensing. Electrical activity of cardiomyocytes cultured on microelectrode arrays was monitored inside a microfluidic system. The chronotropic drug isoproterenol was applied using a robotic dispensing machine, and the resulting changes in spike rate and duration were compared with results gained by experiments with a large scale MEA chip. The experimental findings inspired the development of a technology platform that was finally evaluated by monitoring extracellular signals from myocytes in response to Isoproterenol. Another topic was the comparison of cell-substrate interaction monitored on various electrode structures.
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Wang, Xiaozhi. "Novel applications of carbon nanotubes as micro-electrodes." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611240.
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Sen, Debamoy. "Modeling and simulation of electrochemical magneto hydro dynamics." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Sen_09007dcc8069b391.pdf.
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Thesis (M.S.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 10, 2009) Includes bibliographical references (p. 65-67).
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Hedges, W. M. "The application of microelectrodes to the study of lithium battery systems." Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377950.
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Bin, Shafiee Saiful Arifin. "Fabrication and characterisation of solid titanium nitride and molybdenum nitride microelectrodes." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/419530/.
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Metal nitrides have gained interest due to their high melting point, mechanical resistance, thermal and electrical conductivity. To the best of our knowledge, titanium nitride (TiN) and molybdenum nitride (MoN) electrodes have always been prepared as thin films. However, thin film electrodes tend to delaminate or crack during preparation or usage which exposes the underlying substrate and increases their surface area. In addition, the vapour deposition techniques employed to prepare thin films can introduce contaminants to the samples. In this work we prepared solid metal nitride samples, characterised them with a range of physical methods and investigated their electrochemical properties. Our work demonstrates the feasibility of obtaining TiN and MoN from Ti and Mo foils and microwires via nitridation in a NH3 atmosphere. The process was confirmed using energy dispersive X-ray spectroscopy and X-ray diffraction (XRD). The XRD spectra also showed that hexagonal MoN and cubic Mo2N were obtained. This work also demonstrates the viability of fabricating solid TiN and MoN microelectrodes, microdisks and microbands, from the nitrided Ti and Mo samples. Hence a major objective of the project was to assess whether TiN and MoN could be used as alternatives to conventional microelectrode materials such as Pt, Au, and C. To the extent of our knowledge, MoN and TiN wires have never been used to construct microelectrodes. The electrochemical behaviour of the solid TiN and MoN microelectrodes is assessed using different redox mediators to cover a range of redox potentials. The cyclic voltammograms recorded with the untreated TiN microband electrodes showed that the redox processes at positive potentials were not electrochemically reversible. Yet, the electrochemical response was improved after etching the TiN surface with hydrofluoric acid vapour. In contrast, MoN microelectrodes exhibited sigmoidal shape cyclic voltammograms with a plateau region for all redox mediators even without surface treatment. The TiN and MoN microelectrodes exhibited good activity towards the oxygen reduction reaction recorded in pH 1, 7, 10, and 14. The TiN and MoN microelectrodes were also employed to assess their properties towards the reduction of peroxodisulfate, a very strong oxidising agent with a very complex reduction process. This study also employed bare Au, bare Pt, nanostructured Pt, and bismuth-adsorbed Pt microdisk electrodes to search for the electrode that produces a stable and preferably a diffusion-controlled current for the reduction of peroxodisulfate. Cyclic voltammograms with a plateau region were obtained with the nanostructured Pt, bismuth-modified Pt, HF-etched TiN, and MoN microelectrodes but not with the bare Au and bare Pt microelectrodes. However, only MoN microdisks demonstrated a stable steady-state current for the reduction of peroxodisulfate. To our knowledge, no group has observed cyclic voltammograms with a plateau region when employing bare electrodes for the reduction of peroxodisulfate. A linear relationship between the current and concentration was obtained with the MoN microdisk electrodes for concentrations above 0.1 mM. Similarly, the MoN microdisk electrode produced a diffusion-controlled current for scan rates between 5 and 50 V s-1. Overall, the MoN microelectrodes produced more reliable amperometric results than the TiN microelectrode. Thus, the MoN microelectrodes could be exploited as an alternative to the conventional Pt, Au, and C microelectrodes.
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Potter, Kelsey Ann. "Anti-oxidative Approaches to Improve Neuronal Viability Surrounding Implanted Intracortical Microelectrodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396355468.
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O'Brien, David Patrick. "Micromachined microelectrode arrays for stimulation of neural tissue." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/14993.
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Choi, Yoonsu. "A three-dimensional copuled microelectrode and microfluidic array for neuronal interfacing." Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-05202005-103249/.
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Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2006.Michaels, Thomas E., Committee Member ; LaPlaca, Michelle, Committee Member ; Frazier, A. Bruno, Committee Member ; DeWeerth, Stephen P., Committee Member ; Allen, Mark G., Committee Chair.
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Woodruff, Sarah Louise. "Biomineralisation reactions of algal biofilms at the sediment-water interface." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368647.
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Wang, Shihua. "Structure-function relationship of boron-doped diamond thin-film electrodes and application for in vitro amperometric measurements." Diss., Connect to online resource - MSU authorized users, 2008.
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