Immobilization of catalase on membranes of poly(ethylene)-g-co-acrylic acid and poly(tetrafluoroethylene)-g-co-acrylic acid and their application in hydrogen peroxide electrochemical sensors

The immobilization of catalase on grafted membranes of poly(ethylene)-g-co-acrylic acid and poly(tetrafluoroethylene)-g-co-acrylic acid and their application in hydrogen peroxide electrochemical sensors is described. The introduction of carboxylic acid groups onto a hydrophobic support provides a good environment for subsequent enzyme immobilization. This single membrane, hydrogen peroxide sensor showed significant improvement with respect to the double membrane versions. The response is very rapid, the linear range being from 10 μM up to 6 mM, with a detection limit of 4.7 μM, and a lifetime of more than 4 months.     

Processes associated with ionic current rectification at a 2D-titanate nanosheet deposit on a microhole poly(ethylene terephthalate) substrate

Films of titanate nanosheets (approx. 1.8-nm layer thickness and 200-nm size) having a lamellar structure can form electrolyte-filled semi-permeable channels containing tetrabutylammonium cations. By evaporation of a colloidal solution, persistent deposits are readily formed with approx. 10-μm thickness on a 6-μm-thick poly(ethylene-terephthalate) (PET) substrate with a 20-μm diameter microhole. When immersed in aqueous solution, the titanate nanosheets exhibit a p.z.c. of − 37 mV, consistent with the formation of a cation conducting (semi-permeable) deposit. With a sufficiently low ionic strength in the aqueous electrolyte, ionic current rectification is observed (cationic diode behaviour). Currents can be dissected into (i) electrolyte cation transport, (ii) electrolyte anion transport and (iii) water heterolysis causing additional proton transport. For all types of electrolyte cations, a water heterolysis mechanism is observed. For Ca²⁺ and Mg²⁺ions, water heterolysis causes ion current blocking, presumably due to localised hydroxide-induced precipitation processes. Aqueous NBu₄⁺ is shown to ‘invert’ the diode effect (from cationic to anionic diode). Potential for applications in desalination and/or ion sensing are discussed.

     

Voltammetric studies of the interaction between lead metal ion and the methyl parathion pesticide

Journal of Solid State Electrochemistry - In this work, the interaction of the pesticide methyl parathion (MP) with the lead metal ion was evaluated using a carbon electrode reused from a zinc...     

Voltammetric determination of 17β-estradiol in human urine and buttermilk samples using a simple copper(II) oxide-modified carbon paste electrode

This paper reports the voltammetric determination of 17β-estradiol in urine and buttermilk samples using a simple detector based on a carbon paste electrode (CPE) modified with copper(II) oxide (CuO). The CuO was obtained by the Pechini method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive (EDS), Fourier transform infrared (FTIR), and Raman spectroscopies. Cyclic voltammetry (CV) and square-wave voltammetry (SWV) demonstrated that the CuO-modified carbon paste electrode (CuO/CPE detector) displayed much higher electrocatalytic activity in the 17β-estradiol oxidation reaction than the CPE without modification, exhibiting a low detection limit of 21.0 nmol L^?1 with a wide linear range from 60.0 to 800.0 nmol L^?1 (R = 0.998). Satisfactory results were obtained for the determination of 17β-estradiol in human urine and buttermilk samples. The proposed electrochemical detector offers high repeatability, stability, fast response, low cost, and potential for practical application in the quantification of this hormone.

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Optimization and characterization of a biosensor assembly for detection of <Emphasis Type="Italic">Salmonella</Emphasis> Typhimurium

The performance of biosensors depends directly on the strategies adopted during their development. In this paper, a fast and sensitive biosensor for Salmonella Typhimurium detection was assembled by using optimization studies in separate stages. The pre-treatment assays, biomolecular immobilization (primary antibody and protein A concentrations), and analytical response (hydroquinone and hydrogen peroxide concentrations) were optimized via voltammetric methods. In the biosensor assembly, a gold surface was modified via the self-assembled monolayer technique (SAM) using cysteamine thiol and protein A for immobilization of anti-Salmonella antibody. The analytical response of the biosensor was obtained through the use of a secondary antibody labeled with a peroxidase enzyme, and the signal was evaluated by applying the chronoamperometry technique. The biosensor was characterized by infrared spectroscopy and cyclic voltammetry. Optimization of protein A and primary antibody concentrations enabled higher analytical signals of 7.5 and 75 mg mL^?1, respectively, to be achieved. The hydroquinone and H₂O₂ concentrations selected were 3 and 300 mM, respectively. The biosensor developed attained a very low detection limit of 10 CFU mL^?1 and a fast response with a final detection time of 125 min. These results indicate that this biosensor is very promising for the food safety and emergency response applications.     

A survey of dual-feasible and superadditive functions

Dual-feasible functions are valuable tools that can be used to compute both lower bounds for different combinatorial problems and valid inequalities for integer programs. Several families of functions have been used in the literature. Some of them were defined explicitly, and others not. One of the main objectives of this paper is to survey these functions, and to state results concerning their quality. We clearly identify dominant subsets of functions, i.e. those which may lead to better bounds or stronger cuts. We also describe different frameworks that can be used to create dual-feasible functions. With these frameworks, one can get a dominant function based on other ones. Two new families of dual-feasible functions obtained by applying these methods are proposed in this paper.