A nanoporous gold film (NPGF) was prepared onto a gold electrode surface using a facile and green electrochemical approach via anodization at 2.0 V in 0.5 mol L(-1) H2SO4. The as-synthesized NPGF electrode showed superior electrocatalytic activity towards dissolved oxygen reduction at a low overpotential (-0.045 V) along with 2-fold enhanced sensitivity.
Recebido em 28/6/05; aceito em 18/1/06; publicado na web em 11/8/06 ELECTROCHEMICAL SENSORS: FUNDAMENTALS AND APPLICATIONS IN MICROENVIRONMENTS. Electrochemical sensors have attracted considerable attention in recent years because they provide data about the chemical state of our surroundings and the dynamics of the chemical transformations in the form a spatially resolved image. Particular interest has been directed to measurements in restricted-volume samples as new technologies enable the fabrication of miniaturized versions of sensors with reproducible characteristics. Taking these aspects into consideration, this review focuses on the use of electrodes of micrometer dimensions to acquire chemical information in microdomains in which concentrations may not be spatially homogeneous. This is possible because microelectrodes allow fast-response measurements with micrometer resolution to be performed. On the other hand, the use of microelectrodes as amperometric sensors presents an inherent drawback owing to the insufficient specificity toward the substrate of interest. Hence, some comments on strategies to enhance the selectivity of amperometric sensors are also made. Finally, recent applications of structurally microscopic electrodes as in vivo sensors are shown, as well as a prospect of the future trend in this field.Keywords: electrochemical sensors; microelectrodes; in vivo measurements.
INTRODUÇÃO O atual panorama da EletroanalíticaAs técnicas eletroquímicas constituem-se em poderosa ferramenta para os químicos analíticos na resolução de seus problemas, especialmente por causa de algumas características vantajosas como a elevada sensibilidade das determinações, custo moderado e portabilidade [1][2][3] . A versatilidade das técnicas eletroquímicas também merece destaque visto que é possível controlar as reações eletródicas modificando a interface eletrodo-solução e selecionando-se criteriosamente o potencial aplicado à célula. A facilidade de automação em virtude da medição de sinais elétricos, a possibilidade de proceder à especiação de íons metálicos em certos casos e a "compatibilidade ambiental", pois o reagente empregado é o elétron, também consistem em aspectos que conferem aos métodos eletroanalíticos uma posição de destaque no contexto da Química Analítica.Inerentes às propriedades acima destacadas, aparecem aspectos desvantajosos das medições eletroquímicas, principalmente quando comparadas às efetuadas com técnicas espectroscópicas. Um dos problemas refere-se à interação do eletrodo com a amostra, que em muitos casos ocasiona perda ou irreprodutibilidade nas medidas. O conjunto de compostos passíveis de determinação eletroanalítica também é menos abrangente que no caso das técnicas espectroscópicas. Finalmente, deve-se destacar a natural aversão às técnicas eletroquímicas em razão do sofisticado e nem sempre muito bem compreendido processo heterogêneo de transferência de elétrons que ocorre na interface eletrodo-solução.No atual panorama da Eletroanalítica, pesquisas nas quais se utilizam detector...
The oxidation of Ni(II) and Co(II) tetraglycine complexes in borate buffer aqueous solution, by dissolved oxygen, is strongly accelerated by sulfite. The formation of Ni(III) and Co(III) complexes with maximum absorbances at 327 and 265 nm, respectively, was followed by spectrophotometric measurements. Ni(III) formation was also characterized by voltammetry at low temperatures, whose anodic and cathodic components were observed in the recorded voltammograms. Spectra and rotating ring-disc voltammograms, recorded at various rotation speed values, showed that the Ni(III) species decomposes. The electrochemical process related to the couple Co(II)/Co(III), in a medium containing tetraglycine, was not reversible. In both Ni(II) and Co(II) complexes the metal ion oxidation in the presence of oxygen and sulfite involves the reduction of some initial Ni(III) or Co(III) by sulfite to produce the SO(3).- radical, which rapidly reacts with dissolved oxygen to produce SO(5).-, which then oxidizes Ni(II) or Co(II).
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