Micelle-mediated method for simultaneous determination of ascorbic acid and uric acid by differential pulse voltammetry

The present work describes an analytical methodology for simultaneous determination of ascorbic acid (AA) and uric acid (UA) by differential pulse voltammetry employing the cationic surfactant, cetylpyridinium chloride. Differential pulse voltammetry measurements revealed that the cationic micellar media may separate the oxidation peak potentials of AA and UA present in the same solution by about 282 mV, which is enough to determine both species simultaneously. As in pH 7.0 the AA is more ionized than UA, its electrostatic attraction towards the cationic micelles formed onto the surface of glassy carbon electrode is higher, therefore, promoting a decrease in the overpotential and increasing the electron transfer rate. Calibration curves to AA and UA in the concentration range from 4.70 up to 220 µmol L-1 and 0.50 up to 110 µmol L-1 were built. The proposed methodology was applied for the simultaneous determination of AA and UA in human urine samples

Electrochemical behavior of rhodium acetamidate immobilized on a carbon paste electrode: a hydrazine sensor

The electrochemical behavior of rhodium acetamidate immobilized in carbon paste electrode and the consequences for sensor construction were evaluated. The electrode showed good stability and redox properties. Two reversible redox couples with midpoint potentials between 0.15 and 0.55 V vs SCE were observed. However, peak resolution in voltammetric studies was very dependent on the supporting electrolyte. The correlation between coordinating power of the electrolyte and peak potential suggests that the electrolyte can coordinate through the axial position of the complexes. Furthermore, the axial position may be also the catalytic site, as a catalytical response was observed for hydrazine oxidation. A good linear response range for hydrazine was fit by the equation i = 23.13 (± 0.34) c , where i = current in mA and c = concentration in mol dm-3 in the range of 10-5 up to 10-2 mol dm-3. The low applied potential (<300 mV) indicates a good device for hydrazine sensor, minimizing interference problems. The short response time (~1 s) may be useful in flow injection analysis. Furthermore, this system was very stable presenting good repeatability even after 30 measurements with a variance of 0.5 %.O comportamento eletroquímico do acetamidato de ródio imobilizado em pasta de carbono e as potencialidades para construção de sensores foram avaliados. O complexo imobilizado mostrou boa estabilidade e propriedades redox, sendo observados dois pares redox reversíveis com potenciais médios entre 0,15 e 0,55 V vs SCE. Entretanto, a resolução dos picos voltamétricos mostrou-se dependente do eletrólito suporte. A correlação entre a capacidade coordenante do eletrólito e seus respectivos potenciais médios sugere que o eletrólito deve coordenar-se em posição axial nos complexos. Além disto, a posição axial deve ser o sítio catalítico, sendo que a oxidação de espécies doadoras, como hidrazina, foi catalisada por estes complexos. O baixo potencial (<300 mV) mostra uma boa viabilidade deste composto para a confecção de sensores para a hidrazina, minimizando problemas de interferentes. Uma boa faixa de resposta linear para a hidrazina foi ajustada pela equação i = 23,13 (± 0,34) c , onde i = corrente em mA and c = concentração em mol dm-3 na faixa de 10-5 a 10-2 mol dm-3.O baixo tempo de resposta (~1 s) poderia ser útil em análises por injeção em fluxo. Este sistema foi bem estável e apresentou boa repetibilidade, mesmo após 30 medições, com uma variância de 0,5 %.304310Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

The utilization of materials obtained by the sol-gel process in biosensors construction

The use of sol-gel materials to develop new biosensors has received great attention due to its characteristics and versatility of sol-gel process. An overview is presented of the state-of-the-art of electrochemical biosensors employing sol-gel materials. Low-temperature, porous sol-gel ceramics represent a new class for the immobilization of biomolecules. The rational design of sol-gel sensing materials, based on the judicious choice of the starting alkoxide, encapsulated reagents, and preparation conditions, allows tailoring of material properties in a wide range, and offers great potential for the development of electrochemical biosensors.835841Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Characterization of self-assembled thiols monolayers on gold surface by electrochemical impedance spectroscopy

Thiols with different alkyl chain length and containing COOH terminal group were self-assembled on gold electrodes. The electron transfer of Fe(CN)6(3-/4-) couple to the electrode was studied at different pH by means cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Changes in solution pH resulted in the charge variation of the self-assembled monolayer (SAM) terminal group and, consequently, the electrostatic interaction of SAM with the electroactive species in the solution.Tióis de cadeias carbônicas com tamanhos diferentes e contendo grupo terminal COOH foram usados para formar monocamadas auto-organizadas sobre a superfície de eletrodos de ouro. A transferência de elétrons do par Fe(CN)6(3-/4-) para o eletrodo foi estudada em diferentes pH usando-se as técnicas de voltametria cíclica (CV) e de espectroscopia de impedância eletroquímica (EIS). Mudanças no pH da solução resultaram em variações na carga do grupo terminal das monocamadas auto-organizadas e, conseqüentemente, em alterações na interação eletrostática da SAM com as espécies eletroativas em solução.849855Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Self-assembled monolayers applications for the development of electrochemical sensors

Self-assembled monolayers (SAMs) modified electrodes exhibit unique behavior that can greatly benefit electrochemical sensing. This brief review highlights the applications of SAM modified electrodes in electroanalytical chemistry. After a general introduction, which includes the approaches for SAM development, different electrochemical systems for detecting inorganic and organic species are described and discussed. Special attention to the coupling of biological sensing element to the SAM is given, which can selectively recognize the analyte. Future prospects are also evaluated.381389Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

SPR: New tool for biosensors

This paper reviewed the development and theoretical aspects of surface plasmon ressonance (SPR) technique and discusses this powerful sensor technology in the development of biosensors, as well as for the investigation of biological interactions and clinical assays. The SPR has been proven to be a valuable tool to investigate dynamic processes, such as adsorption, degradation, determination of dieletric properties, association/dissociation kinetics, affinity constants of specific ligand-ligate interactions, allowing real-time analysis at almost any surface. The SPR as a complementary technique alongside electrochemical methods is also presented.9710