A presente dissertação de mestrado tem o propósito de relatar o desenvolvimento de um sensor planar eletroquímico com três eletrodos para o monitoramento de nitrito e seus interferentes (ácido úrico, ácido ascórbico e paracetamol). Para tal, no procedimento experimental é descrito o desenvolvimento do aparato extracorpóreo (mini-bomba compressora, válvulas solenóides e cela de análise). Esse é acoplado a um sistema de Análise por Injeção em Fluxo Automatizada (do inglês, Flow-injection Analysis) FIA-automatizada. Este trabalho também descreve a fabricação dos sensores em substrato de alumina, o processo de limpeza padrão dos eletrodos, o processo de obtenção dos eletrodos de referência em HCl (0,1 mol L-1) e ativação eletroquímica da superfície do eletrodo de trabalho com H2SO4 (0,1 mol L-1). Em seguida, é mostrada a estabilização dos eletrodos de referência Ag/AgCl em solução salina contendo cloretos, o estudo da secagem dos eletrodos em temperatura ambiente com exposição à luz e a caracterização dos mesmos por três métodos distintos, a saber: i) teste de reversibilidade (corrente redox vs. potencial); ii) variação do potencial com o tempo (coeficiente de degradação termodinâmica) e iii) variação do potencial com a concentração de cloretos. Também, apresenta-se a caracterização da área efetiva exposta do eletrodo de medição (trabalho) e os resultados da deposição de 1-2 Diaminobenzeno (DAB) como polímero seletivo. Além disso, são apresentados os resultados e discussões dos pseudo-eletrodos (recoberto ou não com Náfion® 117). Um ponto relacionado, a histerese associada à irreversibilidade dos eletrodos de referência resultou da ordem de 40 mVAg/AgCl Náfion® 117. Os potencias termodinâmicos observados foram da ordem de 100 ± 6 mVAg/AgCl Náfion® 117 para pseudo-eletrodo de referência sem e com Náfion® 117. Depois, foi realizado um estudo criterioso dos potenciais de resposta ao nitrito e aos interferentes por meio da técnica de DPV (do inglês, Differencial Pulse Voltammetry). Para evitar degradação acelerada (corrosão) do polímero sobre o eletrodo de trabalho, optou-se por realizar as medições com potencial igual a 0,50 VAg/AgCl Náfion® 117. Nessa condição, apresenta-se a monitoração de nitrito por FIA-automatizada na faixa de concentração de 50 a 250 mol L-1. Os resultados para a medição de nitrito mostraram que o sensor planar eletroquímico amperométrico desenvolvido é promissor, pois esse apresentou ótimo desempenho de reprodutividade (99,66%), sensibilidade (90 microA mol-1 L mm-2), seletividade (0,32%), repetitividade (91,28%) e estabilidade (15 ± 0,3 pA). / In this Master of Science, it has been developed an electrochemical planar sensor defined with three electrodes for nitrite measuring and its interferents (uric acid, ascorbic acid and paracetamol). In the experimental procedure, it is shown the development of an extracorporis set up (mini-pump, solenoid valves and analysis cell) which is coupled to a system of Flow-injection Analysis (FIA). This work also describes the sensor fabrication using alumina substrates, the standard cleaning of the electrodes, the process to obtain Ag/AgCl reference electrodes in HCl (0.1 mol L-1) and electrochemical activation of the working-electrode surface with H2SO4 (0.1 mol L-1). Following, it is shown the study of drying for electrodes at room temperature with exposition to room light and their characterization using three different methods: i) reversibility test (redox current vs. potential); ii) variation of the potential with the time (thermodynamics degradation coefficient) and iii) variation of the potential with the chloride concentration. Also, it is presented the characterization of the effective exposed area of the working electrode and the results of the deposited 1-2 Diaminobenzene (DAB) is presented as a selective polymer. In addition, the results and discussions of the pseudo-reference (recovered or not with Nafion® 117) are presented. Related to irreversibility is the hysteresis associated to the reference electrodes which resulted in the order of 40 mVAg/AgCl Nafion® 117. The observed thermodynamic potentials were of (100 ± 6) mVAg/AgCl Nafion® 117 for pseudo-electrodes recovered with Nafion® 117. Later on, a careful study of the response to nitrite and to its interferents was performed by means of the DPV technique (Differential Pulse Voltammetry). In order to avoid accelerated degradation (corrosion) of the polymer, measurements were performed at a potential of 0,5 VAg/AgCl Nafion® 117. In this condition, nitrite was monitored using the automatized-FIA (Flow Injection Analysis) for concentration in the range of 50 to 250 mol L-1. The results have shown that the planar amperometric sensor for nitrite measuring is usefull since it was observed excellent performance related to reproducibility (99.66%), sensitivity (90 microA mol-1 L mm-2), selectivity (0.32%), repetibility (91.28%) and stability (15.0 ± 0.3 pA).

We have investigated electropolymerisation for fabrication of a chemically modified working electrode for the determination of dopamine and catechol neurotransmitters in the presence of ascorbic acid. A variety of film compositions were investigated that would allow discrimination of the neurotransmitters through a combination of electrostatic barrier and the film porosity. The films investigated were based on different compositions of () poly-o-toluidine-co-aniline (POT-co-PA), () poly-o-toluidine-co-o-anisidine (POT-co-POA) and () polyacriflavine (PAF). The POT-co-PA and POT-co-POA gave the most promising result although the POT-co-PA was preferred because of higher current enhancement and better separation of dopamine and catechol neurotransmitters in the presence of ascorbic acid. The uses of electropolymerisation make the investigated films attractive candidates for the fabrication of a chemically modified microelectrode with application in capillary electrophoresis separation with electrochemical detection. The active area of nano particle (Au, Pt and Ag) screen printed electrodes was determined using cyclic voltammogram with ferro/ferricyanide couple. The active surface of the nano particle coated electrode was found surprisingly to be 5% - 65% lower than that geometrically calculated surface area for the electrode. This is ascribed to the limitation of the screen printing approach that was used. A low cost high replication approach that would allow development of a capillary electrophoresis microfluidic chip with electrochemical detection (CE-ECD) on a polymer substrate was investigated. A fluidic top layer was fabricated using hot embossing and an electrode bottom layer by metal patterning on a polymer substrate using metallisation and photolithography.

Neste trabalho relata-se pela primeira vez a determinação de adenosina por um biossensor baseado em tirosinase. O biossensor foi desenvolvido mediante a modificação de um eletrodo de carbono impresso (SPE) com nanopartículas de ouro (AuNPs), tirosinase (Tyr) e Nafion, denominado biossensor Nafion/Tyr/AuNPs/SPE. As AuNPs sintetizadas possuem diâmetro médio de 15,0 ± 1,1 nm e sua função é melhorar a via de condução de elétrons entre a enzima e o eletrodo. Utilizou-se o aprisionamento com filme Nafion® para evitar a lixiviação enzimática da superfície do eletrodo. A tirosinase imobilizada apresentou boa atividade frente ao substrato catecol. Verificou-se que a adenosina atua como um inibidor do tipo não-competitivo. O biossensor é estável durante pelo menos 45 dias. Além disso, foi realizada a eletro-oxidação da adenosina para sua determinação. O biossensor apresenta sensibilidade superior em comparação com SPE, AuNPs/SPE e Nafion/AuNPs/SPE. As curvas de calibração revelaram duas faixas lineares para as concentrações de adenosina, de 1,0 × 10-5 mol L-1 até 5,0 × 10-5 mol L-1 e entre 6,0 × 10-5 mol L-1 e 1,2 × 10-4 mol L -1. O limite de detecção (3 × (desvio padrão + média dos brancos)/coeficiente angular da curva) foi de 7,0 × 10-7 mol L-1. / In this work we report for the first time the determination of adenosine by a biosensor based on tyrosinase. The biosensor was developed by modifying a screen-printed carbon electrode (SPE) with gold nanoparticles (AuNPs), tyrosinase (Tyr) and Nafion, denoted as Nafion/Tyr/AuNPs/SPE biosensor. The synthesized AuNPs have a mean diameter of 15.0 ± 1.1 nm and their function is to improve the electron conduction pathway between the enzyme and the electrode. The entrapment with Nafion® film was selected to prevent the enzyme lixiviation from the electrode surface. Immobilized tyrosinase showed good activity with the catechol substrate. It was found that adenosine acts as a non-competitive type inhibitor. The biosensor is stable for at least 45 days. In addition, the electro-oxidation of adenosine was performed for its determination. The biosensor has superior sensitivity compared to SPE, AuNPs/SPE and Nafion/AuNPs/SPE. Calibration curves revealed two linear ranges for adenosine concentrations of 1,010-5 mol L-1 up to 5,010-5 mol L-1 and from 6,010-5 mol L-1 to 1,210-4 mol L-1. The detection limit (3 × (standard deviation + mean of blanks)/slope of the curve) was 7,010-7 mol L-1.

A simple cost-effective approach was proposed and successfully employed to fabricate high-quality screen-printed (SP) contacts to high sheet-resistance emitters (100 ohm/sq) to improve the Si solar cell efficiency. Device modeling was used to quantify the performance enhancement possible from the high sheet-resistance emitter for various cell designs. It was found that for performance enhancement from the high sheet-resistance emitter, certain cell design criteria must be satisfied. Model calculations showed that in order to achieve any performance enhancement over the conventional ~40 ohm/sq emitter, the high sheet resistance emitter solar cell must have a reasonably good (120,000 cm/s) or low front-surface recombination velocity (FSRV). Model calculations were also performed to establish requirements for high fill factors (FFs). The results showed that the series resistance should be less than 0.8 ohm-cm^2, the shunt resistance should be greater than 1000 ohm-cm^2, and the junction leakage current should be less than 25 nA/cm^2. Analytical microscopy and surface analysis techniques were used to study the Ag-Si contact interface of different SP Ag pastes. Physical and electrical properties of SP Ag thick-film contacts were studied and correlated to understand and achieve good-quality ohmic contacts to high sheet-resistance emitters for solar cells. This information was then used to define the criteria for high-quality screen-printed contacts. The role of paste constituents and firing scheme on contact quality were investigated to tailor the high-quality screen-printed contact interface structure that results in high performance solar cells. Results indicated that small particle size, high glass transition temperature, rapid firing and less aggressive glass frit help in producing high-quality contacts. Based on these results high-quality SP contacts with high FFs0.78 on high sheet-resistance emitters were achieved for the first time using a simple single-step firing process. This technology was applied to different substrates (monocrystalline and multicrystalline) and surfaces (textured and planar). Cell efficiencies of ~16.2% on low-cost EFG ribbon substrates were achieved on high sheet-resistance emitters with SP contacts. A record high-efficiency SP solar cell of 19% with textured high sheet-resistance emitter was also fabricated and modeled.

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Neste trabalho relata-se pela primeira vez a determinação de adenosina por um biossensor baseado em tirosinase. O biossensor foi desenvolvido mediante a modificação de um eletrodo de carbono impresso (SPE) com nanopartículas de ouro (AuNPs), tirosinase (Tyr) e Nafion, denominado biossensor Nafion/Tyr/AuNPs/SPE. As AuNPs sintetizadas possuem diâmetro médio de 15,0 ± 1,1 nm e sua função é melhorar a via de condução de elétrons entre a enzima e o eletrodo. Utilizou-se o aprisionamento com filme Nafion® para evitar a lixiviação enzimática da superfície do eletrodo. A tirosinase imobilizada apresentou boa atividade frente ao substrato catecol. Verificou-se que a adenosina atua como um inibidor do tipo não-competitivo. O biossensor é estável durante pelo menos 45 dias. Além disso, foi realizada a eletro-oxidação da adenosina para sua determinação. O biossensor apresenta sensibilidade superior em comparação com SPE, AuNPs/SPE e Nafion/AuNPs/SPE. As curvas de calibração revelaram duas faixas lineares para as concentrações de adenosina, de 1,0 × 10-5 mol L-1 até 5,0 × 10-5 mol L-1 e entre 6,0 × 10-5 mol L-1 e 1,2 × 10-4 mol L -1. O limite de detecção (3 × (desvio padrão + média dos brancos)/coeficiente angular da curva) foi de 7,0 × 10-7 mol L-1. / In this work we report for the first time the determination of adenosine by a biosensor based on tyrosinase. The biosensor was developed by modifying a screen-printed carbon electrode (SPE) with gold nanoparticles (AuNPs), tyrosinase (Tyr) and Nafion, denoted as Nafion/Tyr/AuNPs/SPE biosensor. The synthesized AuNPs have a mean diameter of 15.0 ± 1.1 nm and their function is to improve the electron conduction pathway between the enzyme and the electrode. The entrapment with Nafion® film was selected to prevent the enzyme lixiviation from the electrode surface. Immobilized tyrosinase showed good activity with the catechol substrate. It was found that adenosine acts as a non-competitive type inhibitor. The biosensor is stable for at least 45 days. In addition, the electro-oxidation of adenosine was performed for its determination. The biosensor has superior sensitivity compared to SPE, AuNPs/SPE and Nafion/AuNPs/SPE. Calibration curves revealed two linear ranges for adenosine concentrations of 1,010-5 mol L-1 up to 5,010-5 mol L-1 and from 6,010-5 mol L-1 to 1,210-4 mol L-1. The detection limit (3 × (standard deviation + mean of blanks)/slope of the curve) was 7,010-7 mol L-1.

Neste trabalho relata-se pela primeira vez a determinação de adenosina por um biossensor baseado em tirosinase. O biossensor foi desenvolvido mediante a modificação de um eletrodo de carbono impresso (SPE) com nanopartículas de ouro (AuNPs), tirosinase (Tyr) e Nafion, denominado biossensor Nafion/Tyr/AuNPs/SPE. As AuNPs sintetizadas possuem diâmetro médio de 15,0 ± 1,1 nm e sua função é melhorar a via de condução de elétrons entre a enzima e o eletrodo. Utilizou-se o aprisionamento com filme Nafion® para evitar a lixiviação enzimática da superfície do eletrodo. A tirosinase imobilizada apresentou boa atividade frente ao substrato catecol. Verificou-se que a adenosina atua como um inibidor do tipo não-competitivo. O biossensor é estável durante pelo menos 45 dias. Além disso, foi realizada a eletro-oxidação da adenosina para sua determinação. O biossensor apresenta sensibilidade superior em comparação com SPE, AuNPs/SPE e Nafion/AuNPs/SPE. As curvas de calibração revelaram duas faixas lineares para as concentrações de adenosina, de 1,0 × 10-5 mol L-1 até 5,0 × 10-5 mol L-1 e entre 6,0 × 10-5 mol L-1 e 1,2 × 10-4 mol L -1. O limite de detecção (3 × (desvio padrão + média dos brancos)/coeficiente angular da curva) foi de 7,0 × 10-7 mol L-1. / In this work we report for the first time the determination of adenosine by a biosensor based on tyrosinase. The biosensor was developed by modifying a screen-printed carbon electrode (SPE) with gold nanoparticles (AuNPs), tyrosinase (Tyr) and Nafion, denoted as Nafion/Tyr/AuNPs/SPE biosensor. The synthesized AuNPs have a mean diameter of 15.0 ± 1.1 nm and their function is to improve the electron conduction pathway between the enzyme and the electrode. The entrapment with Nafion® film was selected to prevent the enzyme lixiviation from the electrode surface. Immobilized tyrosinase showed good activity with the catechol substrate. It was found that adenosine acts as a non-competitive type inhibitor. The biosensor is stable for at least 45 days. In addition, the electro-oxidation of adenosine was performed for its determination. The biosensor has superior sensitivity compared to SPE, AuNPs/SPE and Nafion/AuNPs/SPE. Calibration curves revealed two linear ranges for adenosine concentrations of 1,010-5 mol L-1 up to 5,010-5 mol L-1 and from 6,010-5 mol L-1 to 1,210-4 mol L-1. The detection limit (3 × (standard deviation + mean of blanks)/slope of the curve) was 7,010-7 mol L-1.

This thesis pays attention to electrochemical sensors for the detection of glucose. The theoretical part deals with the technology of thick film, their application and firing. It is further described electrochemistry, electrodes used in electrochemistry and analytical methods based on electrochemical reaction. End of theoretical part deals with electrochemical biosensors for detection glucose using special electrodes based on enzyme glucose oxidase. In the experimental part is processed amperometric measure for detection glucose using screenprinted sensors S10 and S8 with immobilized enzyme glucose oxidase. Next was studied effect of plasma, dissolved potassium chloride, storage, ascorbic acid and the reproducibility of the sensors.

Nitrogen-doped carbon materials have garnered much interest due to their electrocatalytic activity towards important reactions such as the reduction of hydrogen peroxide. N-doped carbon materials are typically prepared and deposited on solid conductive supports, which can sometimes involve time-consuming, complex, and/or costly procedures. Here, nitrogen-doped screen-printed carbon electrodes (N-SPCEs) were fabricated directly from a lab-formulated ink composed of graphite that was modified with surface nitrogen groups by a simple soft nitriding technique. N-SPCEs prepared from inexpensive starting materials (graphite powder and urea) demonstrated good electrocatalytic activity towards hydrogen peroxide reduction. Amperometric detection of H2O2 using N-SPCEs with an applied potential of −0.4 V (vs. Ag/AgCl) exhibited good reproducibility and stability as well as a reasonable limit of detection (2.5 µM) and wide linear range (0.020 to 5.3 mM).

Screen printed electrodes (SPEs), which are prepared by patterning conductive inks or pastes onto an insulating support (e.g., plastic film), are widely employed as sensing and biosensing platforms due to their ease of fabrication and relatively low cost. This is especially applicable to electrodes of this nature prepared with carbon-based inks (SPCEs). To date, the most successful and significant commercial application of SPEs has been as test strips for glucose meters. Despite the maturity of this technology, SPE research remains very active as improvements in sensitivity and selectivity, which often involve modifying the electrode surface, hold the key to advancing their utility in routine applications and extending their benefits to other target analytes. Recent studies in the Bishop research group have demonstrated that nitrogen-doped SPCEs (N-SPCEs) exhibit enhanced electrochemical response towards hydrogen peroxide (H2O2), a product of oxidase enzyme (e.g., glucose oxidase, lactate oxidase, etc.) reactions and a common target in biosensing strategies. The presence of nitrogen heteroatoms on the carbon surface facilitates breakage of oxygen-oxygen bonds, a key step in reduction of H2O2. Since previous studies showed only modest incorporation of nitrogen species on SPCEs prepared from commercial ink, these studies aim to investigate the possibility of enhancing N-doping by performing a simple pre-treatment strategy that reportedly increases surface oxygen content of SPCEs prior to N-doping. Since surface oxygen sites have been previously reported to be preferentially modified with nitrogen during N doping strategies, this seems like a promising technique for improving sensitivity of N-SPCEs for H2O2 reduction. To quantify the actuality of these claims, experimental groups were fabricated having undergone no enhancement, pretreatment enhancement only, nitrogen-doping enhancement only, and a combination of the pretreatment and nitrogen-doping enhancements. Here the electrochemical behaviors of pretreated SPCEs, N-SPCEs, and pretreated N-SPCEs for the detection of H2O2 by completing comparative cyclic voltammetry (CV) experiments with and without the presence of H2O2 and with it present in varying concentrations is compared. It is projected that, if successful, the fabricated electrodes that have undergone both the pretreatment protocol and the nitrogen-doping process will have an increased sensitivity and detection limit towards H2O2.