A biosensor based on immobilization of lactate oxidase in a PB-CTAB film for FIA determination of lactate in beer samples

An amperometric lactate biosensor with lactate oxidase immobilized into a Prussian Blue (PB) modified electrode was fabricated. The advantage of using cetyltrimethylammonium bromide (CTAB) in the electrodeposition step of PB films onto glassy carbon surfaces was confirmed taking into account both the stability and sensitivity of the measurements. The biosensor was used in the development of a FIA amperometric method for the determination of lactate. Under optimal operating conditions (pH = 6.9, E = -0.1 V), the linear response of the method was extended up to 0.28 µmol L-1 lactate with a limit of detection of 0.84 mmol L-1. The repeatability of the method for injections of a 0.28 mmol L-1 lactate solution was 2.2 % (n = 18). The usefulness of the method was demonstrated by determining lactate in beer samples and the results were in good agreement with those obtained by using a reference spectrophotometric enzyme method.No presente trabalho são apresentados resultados referentes à fabricação de um biossensor para análise de lactato. O dispositivo foi preparado imobilizando-se a enzima lactato oxidase em filme de Azul da Prússia (PB, sigla em inglês) depositado na superfície de eletrodo de carbono vítreo em soluções de CTAB. Nestas condições experimentais observou-se melhoria na sensibilidade e seletividade das determinações de lactato, as quais foram conduzidas em sistema FIA com detecção amperométrica. Nas condições otimizadas (pH = 6,9 e E = -0,1 V), obteve-se curva analítica com limite superior igual a 0,28 mmol L-1 e um limite de detecção de 0,84 µmol L-1. A repetibilidade do método foi avaliada por meio de injeções consecutivas de amostras de lactato 0,28 mmol L-1, obtendo-se desvio padrão de 2,2 % (n = 18). O método foi aplicado em amostras de cerveja e houve boa concordância entre os resultados obtidos e aqueles oriundos do uso de procedimento espectrofotométrico de referência.Fundação de Amparo à Pesquisa de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

A study of nitrite oxidation at platinum microelectrodes

The anodic oxidation of nitrite at Pt microdisc electrodes (radii 5-25 mm) has been studied. It is shown that the electrode reaction is not simple and the response is determined by the oxide coverage of the surface. It is, however, possible to define conditions for the amperometric determination of nitrite in neutral, aqueous chloride solutions; once the electrode surface is preconditioned, the method is rapid and simple and has a lowest detection limit of » 2 mM

A novel disposable electrochemical microcell: construction and characterization

An alternative technique for the fabrication of disposable electrochemical microcells containing working, reference and auxiliary electrodes on a single device is reported. The procedure is based on thermal-transfer of toner masks onto CD-R (recordable compact discs) gold surfaces to define the layout of the electrodes (contour). In a subsequent step, the layout is manually painted with a permanent marker pen. The unprotected gold surface is conveniently etched (chemical corrosion) and the ink is then easily removed with ethanol, generating gold surfaces without contamination. The final and reproducible area of the electrodes is defined by heat transference of a second toner mask. Silver epoxy is deposited on one of the gold bands which is the satisfactorily used as reference electrode. These microcells were electrochemically characterized by cyclic, linear, and square wave voltammetry, and several electroactive species were used as model systems. The area reproducibility of the electrodes for different microcells was studied and a relative standard deviation better than 1,0% (n = 10) was obtained. Disposable electrochemical microcells were successfully used in analysis of liquid samples with volumes lower than 200 µL and good stability and reproducibility (RSD less than 2.0%) were achieved. These microcells were also evaluated for quantification of paracetamol and dipyrone in pharmaceutical formulations.Este trabalho apresenta uma técnica alternativa de microfabricação para construção de microcélulas eletroquímicas descartáveis contendo os eletrodos de trabalho, auxiliar e de referência em um único dispositivo. Trata-se de um processo simples no qual a termo-transferência de máscaras de toner sobre superfícies de ouro obtidas a partir de discos compactos graváveis (CD-R) definem o formato dos eletrodos (contornos). Numa etapa seguinte, o formato é manualmente coberto com tinta usando uma caneta de retroprojetor. A superfície de ouro não protegida pela tinta é convenientemente removida (corrosão química) e a tinta, por sua vez, é facilmente removida com etanol gerando superfícies de ouro sem contaminação. A área final e reprodutível dos eletrodos é definida pela termo-transferência de uma segunda máscara de toner. O eletrodo de referência é obtido por meio de uma deposição manual de cola de prata sobre uma banda de ouro. As microcélulas foram eletroquimicamente caracterizadas usando as técnicas de voltametria cíclica, voltametria linear e voltametria de onda quadrada e várias espécies eletroativas como sistemas modelo. A reprodutibilidade de área dos eletrodos para diferentes microcélulas foi estudada e um desvio-padrão relativo melhor do que 1,0% foi obtido. As microcélulas descartáveis foram usadas com sucesso para a análise de amostras em volumes menores que 200 µL demonstrando boa estabilidade e reprodutibilidade (RSD menor que 2,0%). Essas microcélulas também foram avaliadas para a quantificação de paracetamol e dipirona em formulações farmacêuticas.(FAPEMIG) Fundação de Amparo à Pesquisa do Estado de Minas GeraisConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

An exceptionally high wave at the CNR-ISMAR oceanographic tower in the Northern Adriatic Sea

On December 15, 2009, a very high wave crest was recorded by a local camera at the CNR-ISMAR oceanographic tower, 15km offshore Venice in the Northern Adriatic Sea (Italy). The height of the estimated crest elevation appears well beyond the value (1,25.H-s) commonly used to identify a wave as freak. We document the wave event with a full description of the corresponding met-ocean conditions and related measurements, of which we provide a critical analysis

Studies on the Electrocatalytic Reduction of Hydrogen Peroxide on a Glassy Carbon Electrode Modified With a Ruthenium Oxide Hexacyanoferrate Film

The electrocatalytic reduction of hydrogen peroxide on a glassy carbon (GC) electrode modified with a ruthenium oxide hexacyanoferrate (RuOHCF) was investigated using rotating disc electrode (RDE) voltammetry aiming to improve the performance of the sensor for hydrogen peroxide detection. The influence of parameters such as rotation speed, film thickness and hydrogen peroxide concentration indicated that the rate of the cross-chemical reaction between Ru(II) centres immobilized into the film and hydrogen peroxide controls the overall process. The kinetic regime could be classified as LSk mechanism, according to the diagnostic table proposed by Albery and Hillman, and the kinetic constant of the mediated process was found to be 706 mol(-1) cm(3) s(-1). In the LSk case the reaction layer is located at a finite layer close to the modifier layer/solution interfaceFAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)[09/07859-1]CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior)CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico

Ultrasensitive microfluidic electrochemical immunosensor based on electrodeposited nanoporous gold for SOX-2 determination

An ultrasensitive and portable microfluidic electrochemical immunosensor for SOX-2 cancer biomarker determination was developed. The selectivity and sensitivity of the sensor were improved by modifying the microfluidic channel. This was accomplished through a physical-chemical treatment to produce a hydrophilic surface, with an increased surface to volume/ratio, where the anti-SOX-2 antibodies can be covalently immobilized. A sputtered gold electrode was used as detector and its surface was activated by using a dynamic hydrogen bubble template method. As a result, a gold nanoporous structure (NPAu) with outstanding properties, like high specific surface area, large pore volume, uniform nanostructure, good conductivity, and excellent electrochemical activity was obtained. SOX-2 present in the sample was bound to the anti-SOX-2 immobilized in the microfluidic channel, and then was labeled with a second antibody marked with horseradish peroxidase (HRP-anti-SOX-2) like a sandwich immunoassay. Finally, an H2O2 + catechol solution was added, and the enzymatic product (quinone) was reduced on the NPAu electrode at +0.1 V (vs. Ag). The current obtained was directly proportional to the SOX-2 concentration in the sample. The detection limit achieved was 30 pg mL−1, and the coefficient of variation was less than 4.75%. Therefore, the microfluidic electrochemical immunosensor is a suitable clinical device for in situ SOX-2 determination in real samples.Fil: Regiart, Daniel Matias Gaston. Universidade de Sao Paulo; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Química de San Luis. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Química de San Luis; ArgentinaFil: Gimenez, Alba Marina. Universidade de Sao Paulo; BrasilFil: Lopes, Alexandre T.. Universidade de Sao Paulo; BrasilFil: Carreño, Marcelo Nelson Paéz. Universidade de Sao Paulo; BrasilFil: Bertotti, Mauro. Universidade de Sao Paulo; Brasi

Electrochemical microfluidic immunosensor based on TES-AuNPs@Fe3O4 and CMK-8 for IgG anti-Toxocara canis determination

We report a microfluidic immunosensor for the electrochemical determination of IgG antibodies anti-Toxocara canis (IgG anti-T. canis). In order to improve the selectivity and sensitivity of the sensor, core-shell gold-ferric oxide nanoparticles (AuNPs@Fe3O4), and ordered mesoporous carbon (CMK-8) in chitosan (CH) were used. IgG anti-T. canis antibodies detection was carried out using a non-competitive immunoassay, in which excretory secretory antigens from T. canis second-stage larvae (TES) were covalently immobilized on AuNPs@Fe3O4. CMK-8-CH and AuNPs@Fe3O4 were characterized by transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometry, cyclic voltammetry, electrochemical impedance spectroscopy, and N2 adsorption-desorption isotherms. Antibodies present in serum samples immunologically reacted with TES, and then were quantified by using a second antibody labeled with horseradish peroxidase (HRP-anti-IgG). HRP catalyzes the reduction from H2O2 to H2O with the subsequent oxidation of catechol (H2Q) to p-benzoquinone (Q). The enzymatic product was detected electrochemically at _100 mV on a modified sputtered gold electrode. The detection limit was 0.10 ng mL−1, and the coefficients of intra- and inter-assay variation were less than 6%, with a total assay time of 20 min. As can be seen, the electrochemical immunosensor is a useful tool for in situ IgG antibodies anti-T. canis determination.Fil: Jofre, Claudio Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Química de San Luis. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Química de San Luis; ArgentinaFil: Regiart, Daniel Matias Gaston. Universidade de Sao Paulo; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Química de San Luis. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Química de San Luis; ArgentinaFil: Fernández Baldo, Martín Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Química de San Luis. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Química de San Luis; ArgentinaFil: Bertotti, Mauro. Universidade de Sao Paulo; BrasilFil: Raba, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Química de San Luis. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Química de San Luis; ArgentinaFil: Messina, Germán Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Química de San Luis. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Química de San Luis; Argentin

Conceitos de química dos ingressantes nos cursos de graduação do Instituto de Química da Universidade de São Paulo

A diagnostic instrument was developed to evaluate the basic chemistry concepts held by freshmen students of the three Chemistry undergraduate courses offered by the University of São Paulo. The instrument minimizes the use of algorithms or memorization by students and values high-order cognitive skills. Analysis of the students' performances reveals systematic use of "displacement reaction" as an algorithm and a mechanical use of Le Chatelier's Principle. Failure in comprehending the chemical equation and chemical language drives students to alternative models for chemical reactions in aqueous solution. For instance, reaction would occur between "ionic pairs" and/or between species situated in separate compartments