With the current interest in alternative methods of energy production and increased utilization of existing energy sources, microbial fuel cells have become an important field of research. Microbial fuel cells are devices which harvest electrons from microorganisms created by their enzymatic oxidation of complex carbon substrates or consumed by their reduction of chemical oxidants. Microbial fuel cells with photosynthetic biocathodes are of particular interest due to their ability to simultaneously produce electricity and hydrocarbons while reducing carbon dioxide. Most species of microorganisms including many bacteria and yeasts require exogenous electron transfer mediators in order to allow electron transfer with an electrode. While adding such chemicals is simple enough at a lab scale, problems arise with chemical costs and separation at a larger scale. The goal of this research was to develop electrodes composed of a robust material which will eliminate the need for added soluble electron mediators in a photosynthetic biocathode microbial fuel cell. Electrodes made from stainless steel 304L have been coated in a conductive polymer (polypyrrole) and an immobilized electron transfer mediator (methylene blue) and tested chemically for stability and in a microbial fuel cell environment for use in bioanodes and biocathodes. The use of these immobilized mediator in the photosynthetic biocathode increased the open circuit voltage of the cell from 0.17 V to 0.24 V and the short circuit current from 8 mA/m2 to 64 mA/m2 (normalized to the geometric surface area of the electrode) when compared to using the same mediator in solution. The opposite effect was seen when using the electrodes in a bioanode utilizing Saccharomyces cerevisiae. The open circuit voltage decreased from 0.37 V to 0.31 V and the short circuit current decreased from 94 mA/m2 to 24 mA/m2 when comparing the immobilized mediator to soluble mediators. The impact of the membrane and pH of the anode and cathode solutions were quantified and were found to have much less of an effect on the internal resistance than the microbial factors.

With the current interest in alternative methods of energy production and increased utilization of existing energy sources, microbial fuel cells have become an important field of research. Microbial fuel cells are devices which harvest electrons from microorganisms created by their enzymatic oxidation of complex carbon substrates or consumed by their reduction of chemical oxidants. Microbial fuel cells with photosynthetic biocathodes are of particular interest due to their ability to simultaneously produce electricity and hydrocarbons while reducing carbon dioxide. Most species of microorganisms including many bacteria and yeasts require exogenous electron transfer mediators in order to allow electron transfer with an electrode. While adding such chemicals is simple enough at a lab scale, problems arise with chemical costs and separation at a larger scale. The goal of this research was to develop electrodes composed of a robust material which will eliminate the need for added soluble electron mediators in a photosynthetic biocathode microbial fuel cell. Electrodes made from stainless steel 304L have been coated in a conductive polymer (polypyrrole) and an immobilized electron transfer mediator (methylene blue) and tested chemically for stability and in a microbial fuel cell environment for use in bioanodes and biocathodes. The use of these immobilized mediator in the photosynthetic biocathode increased the open circuit voltage of the cell from 0.17 V to 0.24 V and the short circuit current from 8 mA/m2 to 64 mA/m2 (normalized to the geometric surface area of the electrode) when compared to using the same mediator in solution. The opposite effect was seen when using the electrodes in a bioanode utilizing Saccharomyces cerevisiae. The open circuit voltage decreased from 0.37 V to 0.31 V and the short circuit current decreased from 94 mA/m2 to 24 mA/m2 when comparing the immobilized mediator to soluble mediators. The impact of the membrane and pH of the anode and cathode solutions were quantified and were found to have much less of an effect on the internal resistance than the microbial factors.

Nanotechnology holds great potential for improving our lives by creating many new materials and devices in medical sciences, electronics and also in energy production. Molecularly imprinted polymers (MIPs) are highly stable synthetic polymers that possess molecular recognition properties due to cavities created in the polymer matrix that are complementary to an analyte both in shape and in positioning of functional groups. These MIPs have been widely employed for diverse applications (e.g., in chromatographic separation, drug screening, chemosensors, catalysis, immunoassays etc) due to their specificity towards the target molecules and high stability against physicochemical perturbations. Conductive polymers, (CPs) such as polypyrrole, can be likened to semiconductors because of small band gaps and low electronic mobility. CPs are exploited as an excellent tool for the preparation of nanocomposites with nano scaled biomolecules. Polypyrrole (Ppy) was the first of this key family of compounds to show high conductivity. So, electrically conducting polypyrrole (Ppy) has numerous applications. In this study, caffeine imprinted electrodes (CIE) were prepared and characterized. This research project mainly focused on three important aspects: &#;To determine the thickness of the polymeric film. &#;To determine the Limit of detection (LOD) of the polymeric film at different conditions. &#;To determine the Analytical Sensitivity (γ) of the polymeric film at varied conditions. In summary these are conclusions stated: •The thickness of the electrode increased with an increase in the number of pulses. The film thickness increased linearly up to an application of 30 pulses and after 30 pulses, an increase in slope occurred with again a linear correlation up to the maximum applied number of pulses, 42. This change in slope may indicate a different mechanism taking place. •LOD is improved as the caffeine load is reduced from 10.0 to 3.0 mM and as the number of pulses is reduced from 36 to 24. •γ increases the number of pulses increase from 24 to 36 and also increases as the caffeine load increases.

L'interès que hi ha per trobar elèctrodes selectius d'ions (ISE) de millors característiques i el fet que l'antibiòtic tetronasina presenta uns equilibris d'intercanvi iònic en solució molt ràpids ens va fer plantejar l'ús d'aquest antibiòtic com a element electroactiu en ISE. La primera part de la investigació realitzada va correspondre a la construcció i avaluació de la resposta d'ISE basats en l'antibiòtic tetronasina per la detecció de l'ió sodi. A priori, aquest ió va ser el primer candidat degut a que els equilibris més ràpids en dissolució es devien a aquest ió. Es va replantejar l'ió principal pels ISE basats en tetronasina desprès de fer un exhaustiu estudi d'interferències, obtenint una resposta pel l'íó calci més gran que per l'ió sodi. El següent pas va ser construir ISE de calci i caracteritzar-los. La formulació òptima de la membrana selectiva d'ió calci emprava un 1% d'ionòfor, 0.2% d'additiu aniònic, 66% oNPOE i 33% PVC. La caracterització per aquests sensors va mostrar una resposta anormalment alta, del doble del predit per la llei de Nernst per ions divalents (65mV/dècada) a pH=5.0.Per la caracterització dels sensors desenvolupats i l'estudi del mecanisme de resposta també es va utilitzar la tècnica de la espectroscòpia electroquímica d'impedàncies. L'estudi de les característiques resistives de les membranes en el rang entre 50KHz-0.05Hz va confirmar l'elecció de la membrana selectiva òptima. El diagrama de Nyquist d'aquesta membrana en contacte amb una solució de CaCl2 10-3M mostrava un únic semicercle corresponent a la resistència oferida per la membrana (resistivitat<700 KOhms·cm) i a la capacitat (98 pF).L'ISE de millors característiques es va utilitzar per construir diferents eines analítiques avançades. La primera aplicació proposada va ser la de construir una llengua electrònica (LE), utilitzant un sistema d'anàlisis per injecció seqüencial (SIA). Aquesta LE tenia el propòsit de determinar Mg2+, Ca2+ i Ba2+ en mostres aquoses mitjançant una matriu formada per 5 sensors. La informació emprada per construir el model de resposta mitjançant xarxes neuronals artificials (XNA) van ser 5 lectures de potencial. La LE permetia la determinació de Mg2+ i Ca2+ en mostres reals.La segona aplicació proposada (també basada en un sistema SIA) va ser la de determinar simultàniament ions alcalins i alcalinoterris mitjançant una LE. Per aquesta proposta es va utilitzar senyals molt més complexes. La informació significativa per construir el model amb XNA es va extreure gràcies a la transformada ràpida de Fourier, emprant uns pocs coeficients de Fourier a l'entrada de la xarxa. La metodologia proposada permetia resoldre mescles de Ca2+, Na+ i K+ amb més precisió que no una LE clàssica.Les ultimes aplicacions assajades es basen també en el concepte de la LE, però aplicada en la detecció del punt d'equivalència de valoracions. En primer lloc es va determinar els ions calci i magnesi de forma simultània mitjançant una matriu de 4 sensors i el processament mitjançant XNA. El mètode proposat consistia en realitzar una valoració molt simple amb EDTA amb els volums fixats (5 addicions). La resposta de la matriu de sensors abans de començar la valoració i després de cada addició es van fer servir per construir el model de resposta. Es va provar la viabilitat d'aquesta metodologia en l'anàlisi simultani de calci i magnesi en mostres reals.Un cop vist els bons resultats d'aquesta nova estratègia es va aplicar el mateix concepte a la multideterminació de tres ions. El procediment seguit va ser el mateix però aplicat a mescles ternàries de Ca2+, Mg2+ i Sr2+. Els resultats obtinguts van mostrar una bona la capacitat de predicció de les concentracions d'aquestes tres espècies en mostres aquoses. / The interest of finding new ion-selective electrodes (ISEs) with better characteristics than the current commercial ones and the fact that the antibiotic ionophoric has fast equilibriums with ions in solution, made us think about the use of this antibiotic as recognition element in ISEs. Tetronasin is a recently isolated ionophoric antibiotic. It is supposed to have a favoured interaction with Sodium, extremely fast, reversible and stable responses were recorded for Calcium. The optimal membrane formulation for Calcium employs 1% ionophore, 0.2% anionic sites, 66% oNPOE and 33% PVC. After extensive characterization of constructed calcium sensors, the response confirmed to be of super-Nernstian nature, with highest value (65mV/decade) at pH=5.0. This behaviour is related to similar antibiotic ionophores with acidic groups, whose sensitivity was designated as "apparently twice-Nernstian response".The mechanisms and responses of the constructed sensors were also studied by means of Electrochemical Impedance Spectroscopy. The characteristics of the membranes in the range 50 KHz-0.05Hz confirmed the election of the optimal membrane. The single semicircle observed on the corresponding Nyquist plots for a calcium chloride 0.001M, is translated into a bulk resistivity lower than 700KOhms·cm, with a geometric capacitance of 98pF.The best tetronasin based ISE was used to build advanced analytical systems. The first application attempted was the simultaneous determination of Magnesium, Calcium, and Barium using a sensor array and multivariate calibration, this combination is known as electronic tongue (ET). The sensor array was formed by five sensors. The subsequent processing of the data was based on the use of a multilayer artificial neural network (ANN). The information needed for training or generation of the model was obtained with the aid of an automated analytical system based on the Sequential Injection Analysis (SIA) technique. The modelling ability was verified with an external set of standards, and next the determinations were performed in real samples of mineral waters, where close results for Magnesium and Calcium were obtained to those obtained with reference methods.The second application was an ET based on the transient response of an array of non-specific-response potentiometric sensors. A SIA system was used in order to automate its training and operation. This work presents the extraction of significant information contained in the transient response of a sensor array using the Fourier transform. The studied case was the analysis of mixtures of calcium, sodium and potassium. Obtained performance is compared with the more traditional automated ET using final steady-state potentials.The last applications proposed are based on the ET concept, but applied in the detection point in titrations. The titration consists in a reduced number of fixed titrant additions to the sample and the recording of the potentials of an array of ISEs. The obtained data matrix is entered to an ANN model, previously trained to furnish concentrations of a multicomponent mixture. The principle is demonstrated with automated EDTA titration of mixtures of Calcium and Magnesium at fixed pH 8.5. In this case, five 2 mL fixed volume additions plus the readings of four sensors were adequate for the resolution of the mixture. The procedure was applied to mineral waters and compared with reference methods.The final application extends the last study for ternary mixtures. The application is demonstrated with ternary mixtures of Calcium, Magnesium and Strontium. In the studied case, good comparisons were observed between obtained and expected concentrations for the three cations with the external validation samples. The proposed procedure was applied to mineral waters and compared with reference methods.

No description available.

Monitoring bio-electric events is a common procedure, which provides medical data required in clinical and research applications. Electrophysiological measurements are applied in diagnosis as well as evaluation of the performance of different body organs and systems, e. g. the heart, muscles and the nervous system. Furthermore, it is staple feature in operation rooms and extensive care units. The performance of the recording system is affected by the tools and instrumentation used and the bio-electrode is a key-player in electrophysiology, hence, the improvements in the electrode recording technique will be directly reflected in the system?s performance in terms of the signal quality, recording duration as well as patient comfort. In this thesis, a design methodology for micro-spike array dry bio-electrodes is introduced. <br /><br /> The purpose of this methodology is to meet the design specifications for portable long-term EEG recording and optimize the electrical performance of the electrodes by maximizing the electrode-skin contact surface area, while fulfilling design constraints including mechanical, physiological and economical limitations. This was followed by proposing a low cost fabrication technique to implement the electrodes. The proposed electrode design has a potential impact in enhancing the performance of the current recording systems, and also suits portable monitoring and long term recording devices. The design process was aided by using a software design and optimization tool, which was specifically created for this application. <br /><br /> The application conditions added challenges to the electrode design in order to meet the required performance requirements. On the other hand, the required design specifications are not fulfilled in the current electrode technologies which are designed and customized only for short term clinical recordings. <br /><br /> The electrode theory of application was verified using an experimental setup for an electrochemical cell, but the overall performance including measuring the electrode impedance is awaiting a clinical trial.

Hot microelectrodes are very small electrodes (usually 1 100 µm in diameter), which have a surface temperature much higher than the temperature in the bulk solution. In this work, the heating is achieved by applying an alternating potential of very high frequency (100 MHz 2 GHz) and of high amplitude (up to 2.8 Vrms) to the microelectrode. As a result, very fast (on the order of milliseconds) changes in the temperature of the electrolyte solution surrounding the electrode can be achieved. Due to the size of the heated microelectrodes, the hot zone in solution is small. Therefore, the solution can be easily overheated and temperatures above the boiling point can be reached.<p> The purpose of this research was to investigate and understand the phenomena occurring at ac polarized microelectrodes and to propose new applications of these electrodes. Using both steady-state and fast-scan (10 V/s) cyclic voltammetry measurements, mass transport of redox species has been studied at ac heated microelectrodes. It has been established that the convection at hot-disk microelectrodes is driven primarily by the electrothermal flow of an electrolyte solution. In addition, other effects such as ac dielectrophoresis and Soret (nonisothermal) diffusion are also observed. Numerical simulations have been employed to predict the distribution of temperature in the hot zone, the direction and magnitude of the electrothermal force and the solution flow rate, as well as the voltammetric response of hot-disk microelectrodes. The results of the simulations agree well with the experimental observations. Theoretical findings of this PhD work are very important for the understanding of the fundamentals of high temperature electrochemistry, particularly mass transport. The proposed explanation of the convection mechanism is most likely applicable not only to ac polarized microelectrodes, but also to the microwave heated microelectrodes, since the only difference between these two heating methods is in the way of delivering electrical energy (wired vs. wireless). The results of the studies of Soret diffusion indicate that it contributes significantly to mass transfer of redox species at hot microelectrodes. Taking into account that the magnitude of the Soret effect has been considered negligible by other electrochemists, the results obtained in this work prove the opposite and show that Soret diffusion affects both the faradaic current and the half-wave potential of the redox reaction. Therefore, the Soret effect can not be ignored if working with hot microelectrodes.<p> Hot microelectrodes can have a number of interesting applications. The results of the initial investigations indicate that these electrodes can be successfully used in the arrangement for Scanning Electrochemical Microscopy (such a novel technique is termed Hot-Tip SECM). In addition, the observed dielectrophoretic and electrothermal convection effects can enhance the performance of the electrochemical sensors based on hot microelectrodes. This can lead to the improvement of the detection limits of many biologically important analytes, such as proteins, bacteria and viruses.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Ceramic and Materials Science and Engineering." Includes bibliographical references.

Thesis (M.Sc.(Chemistry))--University of Pretoria, 2006. / Includes abstract in English. Includes bibliographical references.

Thesis (Ph.D.(Chemistry))--University of Pretoria, 2004. / Summaries in English and Afrikaans. Includes bibliographical references (leaves 229-238). Also available online.