This thesis ties some electrochemical aspects of development and fabrication of an analytical system on a microchip together. These aspects develop through the fundamentals of amperometric detection in microsystems and microfabrication via the interaction of electrochemical detection and electrophoretic separation finally to the interfacing of a microsystem to the macro world. Paper I deals with amperometric detection in microscale systems and describes the fabrication of the necessary on-chip microelectrodes together with fluidic channels in silicon. It was furthermore studied, if the interelectrode distance of some μm could be used to improve the sensitivity in amperometric detection by employing redox cycling. Papers II, III and IV deal with the effect of a high voltage field on amperometric detection. In analytical microdevices typically an electrophoretic separation step (e.g. capillary electrophoresis, CE) precedes the detection. The interference of the CE high voltage with the amperometric detection potential is often considered one of the main hindrances for an effective combination of these techniques. In paper II one reason for the observed disturbing potential shift was elucidated. It was shown that positioning of working electrode and reference electrode on an equipotiental surface eliminates this problem. Paper III reports an application of this technique. In paper IV it could be shown that this approach could further be used to significantly reduce the instrumental requirements for amperometric detection in CE. Papers V, VI, VII, finally discuss the interfacing of low volumetric flows that typically occur on microanalytical devices to other techniques. Both, interfacing from liquid to liquid phase (μLC to CE in paper V) and from liquid to gas phase (CE to MS in paper VI and VII) were discussed. Electrochemical methods are used in this context to evaluate the stability and, in paper VI and VII, to increase the understanding of underlying processes of corrosion.

Les neuropathies périphériques sont des dysfonctions causées par certaines maladies (diabète, mucoviscidose). Celles-ci peuvent être rapidement diagnostiquées par la technologie SudoscanTM. Cette technologie non invasive, est basée sur des mesures électrochimiques via l’imposition de faibles potentiels entre des électrodes appliquées sur la peau et la mesure de faibles courants. Les résultats obtenus sont liés à la composition de la sueur associée à l’innervation des glandes sudoripares. Les résultats obtenus in vivo donnent une réponse caractéristique à l’anode, qui permet de déterminer le type de maladie et son avancement. Afin de mieux comprendre les phénomènes mis en jeu aux électrodes et d’optimiser la sensibilité des mesures in vivo, des manipulations ont été réalisées in vitro dans des solutions mimant la composition de la sueur. Pour simuler la résistance du corps et réduire les densités de courant obtenues in vitro la viscosité de l’électrolyte a été augmentée. Cet électrolyte a permis d’atteindre des densités de courant in vitro proches de celles obtenues in vivo. Le second objectif de cette étude est d’analyser le comportement électrochimique in vitro de différents aciers inoxydables biocompatibles et leur résistance à la corrosion dans un milieu physiologique à pH neutre. Nous nous sommes plus précisément intéressés à l’influence de la concentration en ions chlorure sur la corrosion, aux échelles de concentrations trouvées dans la sueur, (36mM 120mM). L’objectif est de permettre une meilleure compréhension des phénomènes mis en jeu et d’analyser la sensibilité des matériaux aux ions chlorures, pour déterminer le matériau le plus prometteur pour la technologie. / A non-invasive device based on measurements of electrochemical skin conductance can detect small fiber neuropathy, a sweat gland dysfunction implicated in several diseases. In this context, the SudoscanTM technology developed by Impeto Medical provides early diagnosis, rapid and noninvasive analysis. This technology is based on measurements of skin current density via the imposition of low amplitude voltages (4 to 1.5V) between electrodes applied to the skin and measuring the low current generated. These electrodes are sensitive to the composition of the sweat produced by the eccrine glands when stimulated. The results obtained in vivo provide a characteristic response on the anode, which determines the type of disease and its progress. To better understand the phenomena involved at electrodes and to optimize the sensitivity of in vivo measurements, manipulations were performed in vitro with solutions mimicking the composition of the sweat. To simulate the resistance of the body and to reduce the current densities obtained in vitro, the viscosity of the electrolyte has been increased. This electrolyte has achieved in vitro current densities similar to those obtained in vivo. The second objective of this study is to analyze the electrochemical behavior of different biocompatible stainless steels and their corrosion resistance in a physiological medium at neutral pH. We specifically interested in the influence of the chloride ion concentration on the corrosion, in the range of sweat’s. The objective is to enable a better understanding of the phenomena involved and analyze the sensitivity of materials to chloride ions, to determine the most promising material for technology.

In recent years, there has been a dramatic increase in the use of improvised explosive devices (IEDs) due to ease of synthesis and improved controls placed on commercial/military explosives. Commonly used materials for IED preparations include fertilizers and industrial chemicals containing oxidizers such as ClO3-, ClO4-, and NO3-, as well as other less stable compounds, such as peroxides. Due to these materials having a wide range of volatility, polarity, and composition, detection can be challenging, increasing the amount of time before any analytical information on the identity of the explosive can be determined. Therefore, this research project developed two analytical methods to aid in the rapid detection of multiple explosive compounds. The use of microfluidic paper-based analytical devices (µPADs) allows for the development of inexpensive paper devices utilizing colorimetric reactions, which can perform five or more simultaneous analyses in approximately five minutes. Two devices were developed: one for the detection of inorganic explosives including ClO3-, ClO4-, NH4+, NO3-, and NO2-, and the second device detects high/organic explosives including RDX, TNT, urea nitrate, and peroxides. Limits of detection ranged from 0.4 µg – 20 µg of explosive residue with an analysis time of less than five minutes. Development of a confirmatory method utilizing infusion electrochemical detection-electrospray ionization-time-of-flight mass spectrometry (EC-ESI-TOF MS) and 18-crown-6 ethers to produce guest/host complexes with inorganic ions has also been completed. Utilizing this method the inorganic ions present in many IEDs can be successfully detected as ion pairs, while still allowing for the detection of other high explosives1. Placing an electrochemical detector before the mass spectrometer permits the detection of hydrogen peroxide, an analyte normally difficult to detect through mass spectrometry. Limits of detection ranged from 0.06 ppm - 2 ppm with an analysis time of less than two minutes. The development of these presumptive and confirmatory analytical methods permits the detection of a wide range of components present in IEDs. These methods decrease the amount of time required to relay information on the type of explosives present by simplifying the analysis process in the field and in a laboratory.

Dans le cadre d’une thèse en cotutelle qui a démarré en Janvier 2013, j'ai développé des biopuces ultra-sensibles pour la détection de maladies infectieuses (Tuberculose et Hepatite C). Ce sujet, qui combine recherche fondamentale et recherche appliquée dans pour le diagnostic précoce de maladies, avait pour but la détection rapide d’espèces chimiques fortement diluées dans un liquide biologique. Cette détection se fait de manière électrochimique, grâce à l’utilisation des nanomatériaux carbonés innovants (feuillets de graphène, nanotubes de carbone (NTCS)) qui sont dotés d’une conductivité électronique élevée. J’intègre ces nanomatériaux par des procédés de micro/nanofabrication sur des électrodes de travail dans des cellules microfluidiques. J'ai démontré qu'en combinant un haut flux et un transducteur en NTCs qu'il est possible d'augmenter de 3 ordres de grandeur la sensibilité de détection dans la chambre fluidique (article soumis à LoC). J'ai aussi étudié par spectroscopîe d'impédance la nature du transfert des charges entre l'électrolyte et la graphène (2ème article en cours de rédaction). Mon doctorat a donc validé une technologie innovante pour les biocapteurs miniaturisés à ADN, avec un fort potentiel de valorisation, dans le domaine de la santé et de l’environnement. / As part of my thesis under joint supervision between UPS and Sfax Universities which started in January 2013, I developed ultra-sensitive biochips for the detection of infectious diseases (Tuberculosis and Hepatitis C). This subject, which combines basic and applied research for the early detection of diseases, aimed rapid detection of highly diluted chemical species such as DNA in a biological fluid. This detection is done electrochemically, through the use of innovative carbon nanomaterials (graphene layers, carbon nanotubes (NTCS)) which are provided with a high electron conductivity. I have integrated these nanomaterials by micro / nano-fabrication processes on working electrodes in microfluidic cells. I demonstrated that by combining a high flow and a that CNTs as transducer, the sensitivity of detection in the fluid chamber can be increased by 3 orders of magnitude (Article submitted to Lab on Chip journal). I also studied by impedance spectroscopy the nature of the charge transfer between the electrolyte and the graphene (2nd article being drafted). My PhD has validated an innovative technology for miniaturized biosensors DNA, with a strong development potential in the field of health and the environment.

This thesis work aims to develop electrochemical sensors for sub-ppb level detection of inorganic and organic pollutants in drinking water with environmentally benign materials and processes. While traditional laboratory-based methods such as mass spectroscopy, and chromatography have been used to analyze the concentration of contaminants in drinking water, miniaturized electrochemical sensors offer a compelling alternative to those methods, enabling rapid on-site cost-effective detection of low concentrations of pollutants. In this research, a set of three-electrode sensors was designed and fabricated on a flexible substrate using a screen-printing technique. Additionally, an in-situ electrochlorination process was implemented to create the reference electrode. These sensors were utilized to precisely detect lead ions and perfluorooctane sulfonate (PFOS) in drinking water. The first set of sensors was fabricated to measure the concentration of lead ions, a toxic inorganic pollutant, in potable water. The novelty of the proposed research lies in using non-toxic, biodegradable sodium alginate grafted with 2- acrylamido-2-methyl propane sulfonic acid (AMPS) and conductive fillers for trace-level lead ion detection in water. The principle of square wave anodic square wave stripping voltammetry (SWASV) was used to determine the trace level lead ion concentration. Employing a similar approach with a different material, a PFOS sensor was developed. Utilizing chitosan, one of the sustainable and biodegradable biopolymers found in crustacean shells, rapid parts-per-trillion (ppt) level PFOS detection by electrochemical impedance spectroscopy (EIS) was demonstrated. The proposed sensors made low-cost electrochemical detection of contaminants such as lead ions and PFOS possible with eco-friendly materials and processes.

No description available.

Among the organic electronic conducting organic polymers PEDOT (poly(3,4- ethylenedioxythiophene)) is largely used in the making of electrodes for miniaturized, light and portable devices. The chemical, mechanical, electrochemical and optical properties of the conducting polymers are essential to plan the future research with them, as in, e.g., electrochromic devices (transmissive and reflective), chronoamperometric sensors, voltammetric sensors and controlled drug release systems. Degradability is also an important factor considering the environmental impact of the materials. Nanoparticles (NPs) of Au or Pt (1−100 nm size), when surrounded by a stabilizer, are stable, have reactive and functionalizable surfaces and catalyze many electron transfer reactions. Combinations of noble metal nanoparticles with PEDOTs (PEDOT and its derivatives) have been studied in the last years to obtain singular characteristics of the materials. The goals of this work are to study the synthesis of new inorganic/organic hybrids and their electrochemical behavior. Through 1-step oxidoreduction reaction in aqueous media, hybrids of core-shell Au@PEDOT nanoparticles were synthesized. Through this same strategy, nanoparticles of Pt dispersed in a matrix of PEDOT were synthesized. The Au@PEDOT nanoparticles had their electrochromic behavior studied. With the biodegradable macromonomer EDOTpoly(lactic acid) (EDOT-PLA) were prepared hybrids of NPsAu/(oligomers of EDOTPLA) and also of NPsAu with the new polymer PEDOT-PLA. The produced materials were analyzed. The nanoparticles are very small, with a maximum of distribution in less than 10 nm. Its observed that PEDOT-PLA is conducting, electronically similar to PEDOT and insoluble in water. It is also more stable as a film than PEDOT. NPsAu/PEDOT-PLA demonstrates to have electrocatalytic towards the reduction of hydrogen peroxide. Electrodes of high performance towards the reduction of hydrogen peroxide were thus obtained (sensitivity 8.4x10-3 A cm-2 mol-1 L; linear range (5.1x10-4 − 4.5x10-2) mol L-1; limit of detection 1.7x10-4 mol L-1). Syntheses of acrylic hydrogels and the insertion of nanoparticles/PEDOT in them were also performed, modifying their properties. / Entre os polímeros orgânicos condutores eletrônicos o PEDOT (poli(3,4- etilenodioxitiofeno)) é largamente utilizado na fabricação de eletrodos em dispositivos miniaturizados, leves e portáteis. As propriedades químicas, mecânicas, eletroquímicas e ópticas dos polímeros condutores são essenciais para planejar a pesquisa futura com eles, e.g., em dispositivos eletrocrômicos transmissivos e reflexivos, sensores cronoamperométricos, sensores voltamétricos e sistemas de liberação controlada de drogas. Degradabilidade também é um fator importante ao considerar o impacto ambiental dos materiais. Nanopartículas (NPs) de Au ou Pt (1−100 nm de tamanho), quando revestidas por um estabilizante, são estáveis, possuem superfícies reativas e funcionalizáveis e catalisam muitas reações de transferência de elétrons. As combinações de nanopartículas de metais nobres com PEDOTs (PEDOT e seus derivados) vêm sendo bastante estudadas nos últimos anos de forma a obter características singulares dos materiais. Os objetivos deste trabalho são estudar a síntese de novos híbridos inorgânicos/orgânicos e o seu comportamento eletroquímico. Foram sintetizados, por reação de oxidorredução em uma etapa em meio aquoso, híbridos de nanopartículas core-shell de Au@PEDOT. Por esta mesma estratégia, nanopartículas de Pt dispersas em matrizes de PEDOT foram sintetizadas. As nanopartículas de Au@PEDOT tiveram o seu comportamento eletrocrômico estudado. Com o macromonômero biodegradável EDOT-poli(ácido lático) (EDOT-PLA) foram preparados híbridos de NPsAu/(oligômeros de EDOT-PLA) e também de NPsAu com o novo polímero PEDOT-PLA. Os materiais produzidos foram analisados. As nanopartículas são muito pequenas, com um máximo de distribuição em menos de 10 nm. Observa-se que o PEDOT-PLA é um condutor, de estrutura eletrônica semelhante ao PEDOT e insolúvel em água. Ele também é mais estável em filme do que o PEDOT. NPsAu/PEDOT-PLA demonstra ter atividade eletrocatalítica de redução do peróxido de hidrogênio. Eletrodos de alto desempenho para a redução de peróxido de hidrogênio foram, portanto, obtidos (sensibilidade 8,4x10-3 A cm-2 mol-1 L; faixa linear (5,1x10-4 4,5x10-2) mol L-1; limite de detecção 1,7x10-4 mol L-1). Foram feitas também sínteses de hidrogeis acrílicos e a inserção de nanopartículas/PEDOT neles, modificando as suas propriedades.

None.

The work presented in the thesis is about the evaluation of Organic Electrochemical Transistors (OECTs) for fast scan cyclic voltammetry (FSCV). FSCV is a method which has been used for real time dopamine sensing both in vivo and in vitro. The method is sensitive to noise and could therefore benefit from signal preamplification at the point of sensing, which could be achieved by incorporation of OECTs. In this study the OECTs are based on the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The gate consists of gold microelectrodes of different sizes to be used one at a time. When dopamine is reacted at the gate electrode, the redox state of the PEDOT:PSS OECT channel is modulated and the resulting change in drain current can be measured. The gate current, which contains the sensing information, is after filtering obtained by differentiating the channel potential with respect to time. The derived gate current is plotted in cyclic voltammogram for different dopamine concentrations and the amplitude of the oxidation/reduction peaks can be used to determine the dopamine concentration. In this thesis for the first time it is demonstrated that OECTs can be used for FSCV detection of dopamine. The results are discussed and an outlook on future work is given.

Made available in DSpace on 2014-06-11T19:29:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T19:38:10Z : No. of bitstreams: 1 okumura_ll_me_araiq.pdf: 737796 bytes, checksum: fb5e89571c23b9fd419cea4f1ac1559e (MD5) / O comportamento cíclico voltamétrico do acetaldeído e seu derivado foi estudado em eletrodo de gota pendente de mercúrio e carbono vítreo. Este estudo foi utilizado na otimização das condições para a detecção eletroquímica desses compostos por Cromatografia Líquida de Alta Eficiência (C.L.A.E.). O acetaldeído foi derivado com 2,4-dinitrofenilhidrazina (DNPHi) e o produto, a 2,4-dinitrofenilhidrazona do acetaldeído (AcH-DNPHo) foi eluida e separada por coluna de fase reversa C18 em condições isocráticas com fase móvel contendo uma mistura binária de metanol-solução aquosa de cloreto de lítio (LiCl) com concentração de 1,0 ´ 10-3 M (80:20% v/v) e vazão de 1,0 mL min-1. A detecção eletroquímica (D.E.) do AcH-DNPHo foi realizada por C.L.A.E. com potencial fixado em + 1,0 V vs eletrodo de referência Ag/AgCl. O método proposto foi simples, rápido (tempo de análise 7 min.), com limite de detecção 3,80 mg L-1, altamente seletivo, e reprodutível [desvio padrão relativo 8,2% (n=12)]. A curva analítica do AcH-DNPHo foi linear na faixa compreendida de 0 - 300 mg L-1, com índice de correlação linear 0,9998. A concentração de acetaldeído determinada em amostras de álcool combustível foi de 83 – 341 mg L–1 com desvio padrão de 1 – 6 %, na variação da área de pico e recuperação superior a 99%. A quantidade do teor de acetaldeído encontrado nestas amostras foi significativamente alta e os resultados obtidos foram comparados com o método de detecção espectrofotométrica (UV/Vis) / The cyclic voltammetric behaviour of acetaldehyde and their derivatives has been studied at a hanging drop mercury and glassy carbon electrode. This study was used to optimise the conditions for the electrochemical detection of these compounds following high-performance liquid chromatographic (H.P.L.C.) separation. The acetaldehyde was derivatized with 2,4-dinitrophenylhydrazine (DNPHi) and the product 2,4-dinitrophenylhydrazone (AcH-DNPHo) was eluted and separated by reversed-phase column C18 in isocratic conditions with mobile phase containing binary mixture of methanol-chloride littium aqueous solution with concentration 1,0 ´ 10-3 M (80:20% v/v) and flow rate of 1.0 mL min-1. The electrochemical detection (E.D.) of AcH-DNPHo was performed by H.P.L.C. set at +1.0 V vs Ag/AgCl as reference electrode. The proposed method was simple, rapid (analysis time 7 min), with detection limit 3.80 mg L-1, highly selective, and reproducible [relative standard deviation 8.2 % (n=12)]. The calibration graph for AcH-DNPHo was linear in the range of 0 – 300 mg L-1 with correlation coefficient 0,9998. The concentrations of acetaldehyde determined in fuel alcohol samples was in the range of 83 – 341 mg L–1 with standard deviation of 1 – 6 %, in peak area variation and analytical recovery was >99%. The amount of acetaldehyde content found in these samples was significantly higher and the results obtained were compared to the spectrofotometric detection method (UV/Vis)