One-step electrochemical synthesis of nitrogen and sulfur co-doped, high-quality graphene oxide.

High-quality graphene oxide (GO) with high crystallinity and electrical conductivity as well as in situ doped with nitrogen and sulfur is obtained via the electrochemical exfoliation of graphite. Furthermore, iron incorporated GO sheets show promising catalytic activity and stable methanol tolerance durability when used as electrocatalysts for the oxygen reduction reaction.

Using cavity microelectrodes for electrochemical noise studies of oxygen-evolving catalysts.

Cavity microelectrodes were used as a binder-free platform to evaluate oxygen evolution reaction (OER) electrocatalysts with respect to gas bubble formation and departure. Electrochemical noise measurements were performed by using RuO2 as a benchmark catalyst and the perovskite La0.58 Sr0.4 Fe0.8 Co0.2 O3 as a non-noble metal OER catalyst with lower intrinsic conductivity. Changes in the current during the OER originate from variations in electrolyte resistance during the formation of the gas phase and partial coverage of the active area. Fluctuations observed in current and conductance transients were used to establish the contribution from the ohmic overpotential and to determine the characteristic frequency of oxygen evolution. The proposed quantitative determination of gas bubble growth and departure opens up the route for a rational interface design by considering gas bubble growth and departure as a main contributing factor to the overall electrocatalytic activity at high current densities.

Activation of oxygen evolving perovskites for oxygen reduction by functionalization with Fe-N(x)/C groups.

The incorporation of Fe-Nx/C moieties into perovskites remarkably activates them for the oxygen reduction reaction (ORR) and also leads to notable improvement of their activity towards the oxygen evolution reaction (OER) thus presenting a new route for realizing high performance, low cost bifunctional catalysts for reversible oxygen electrodes.

Local visualization of catalytic activity at gas evolving electrodes using frequency-dependent scanning electrochemical microscopy.

A new concept for the localized characterization of gas evolving electrodes based on scanning electrochemical microscopy (SECM) is suggested. It offers information about the spatial distribution of the predominant locations, which represent the most active catalytic sites, and dynamic characteristics of gas-bubble departure. The knowledge about gas-bubble departure is critical for the assessment and development of new electrode materials for energy applications.

Evaluation of perovskites as electrocatalysts for the oxygen evolution reaction.

The oxygen evolution reaction (OER) is an enabling process for technologies in the area of energy conversion and storage, but its slow kinetics limits its efficiency. We performed an electrochemical evaluation of 14 different perovskites of variable composition and stoichiometry as OER electrocatalysts in alkaline media. We particularly focused on improved methods for a reliable comparison of catalyst activity. From initial electrochemical results we selected the most active samples for further optimization of electrode preparation and testing. An inverted cell configuration facilitated gas bubble detachment and thus minimized blockage of the active surface area. We describe parameters, such as the presence of specific cations, stoichiometry, and conductivity, that are important for obtaining electroactive perovskites for OER. Conductive additives enhanced the current and decreased the apparent overpotential of OER for one of the most active samples (La(0.58)Sr(0.4)Fe(0.8)Co(0.2)O(3)).

Enzymatic fuel cells: integrating flow-through anode and air-breathing cathode into a membrane-less biofuel cell design.

One of the key goals of enzymatic biofuel cells research has been the development of a fully enzymatic biofuel cell that operates under a continuous flow-through regime. Here, we present our work on achieving this task. Two NAD(+)-dependent dehydrogenase enzymes; malate dehydrogenase (MDH) and alcohol dehydrogenase (ADH) were independently coupled with poly-methylene green (poly-MG) catalyst for biofuel cell anode fabrication. A fungal laccase that catalyzes oxygen reduction via direct electron transfer (DET) was used as an air-breathing cathode. This completes a fully enzymatic biofuel cell that operates in a flow-through mode of fuel supply polarized against an air-breathing bio-cathode. The combined, enzymatic, MDH-laccase biofuel cell operated with an open circuit voltage (OCV) of 0.584 V, whereas the ADH-laccase biofuel cell sustained an OCV of 0.618 V. Maximum volumetric power densities approaching 20 µW cm(-3) are reported, and characterization criteria that will aid in future optimization are discussed.

Methylene green electrodeposited on SWNTs-based "bucky" papers for NADH and l-malate oxidation.

This research introduces a cavity anode design based on new single-walled nanotube (SWNTs) papers, "bucky" papers, used for the oxidation (and regeneration) of nicotinamide adenine dinucleotide (NADH) and the oxidation of l-malate. The materials designed are paper-like processed composites containing also additives: BP11 sample contains SWNTs and isopropanol (IPA); the BPMG sample contains SWNTs, IPA, and methylene green (MG). NADH/NAD(+) is the cofactor responsible for the oxidation of l-malate by malate dehydrogenase (MDH), in the Krebs' cycle. Because of the high overpotential of NADH oxidation, poly methylene green (PMG) was utilized as the electrocatalyst to produce NAD(+). The electrocatalyst was deposited on the surface of the "bucky" papers by electropolymerization by means of 10 voltammetric cycles in a range of -0.5 V and +1.3 V (vs Ag/AgCl reference electrode) at a scan rate of 5 mV/s. The catalytic performance of PMG was evaluated by chronoamperometric measurements of NADH oxidation at 0.3 V in phosphate buffer and l-malate oxidation at 0.1 V in the presence of MDH. For both "bucky" papers, the chronoamperometric curves of PMG, current vs NADH concentration, show a linear relationship demonstrating to have a first order Fick's law behavior for concentrations of NADH lower than 6 mM. The chronoamperometric curves in the presence of MDH, current against l-malate concentration, show a Michaelis-Menten behavior where no inhibition or competitive reaction are detected. Additionally, the anodic materials were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), the polymerization of MG is effectively observed in the form of particles nucleation. The anodes show an excellent electrocatalytic activity toward NADH oxidation. The electrode design is feasible, reproducible, and overall stable.

[Evaluation of oppositional defiant symptoms in 6- to 8 year-old children: Agreement between parents and teachers]. / Evaluación de la sintomatología negativista desafi ante en niños de seis a ocho años: concordancia entre padres y maestros.

The main goal of this study is to determine the degree of agreement between the reports provided by parents and teachers about oppositional defiant symptoms in school children between the ages of 6 and 8 years. In addition, it attempts to determine whether children's age and sex affect the level of agreement between informants. Parents and teachers assessed 702 girls and boys at 25 schools in the Region of Osona, Barcelona (Spain) with the Child Symptom Inventory-4 (parents' and teachers' version). The results indicate a very low agreement -practically null- between the valuations of both informants; furthermore, no significant difference due to the variables age and sex of the children was observed in the above-mentioned valuations. The parents tended to appraise most of the symptoms of the Oppositional Defiant Disorder as present and to evaluate their severity as being more intense.

Evaluación de la sintomatología negativista desafiante en niños de seis a ocho años: concordancia entre padres y maestros / Evaluation of oppositional defiant symptoms in 6- to 8 year-old children: Agreement between parents and teachers

El objetivo principal de este estudio es conocer el grado de concordancia entre los informes proporcionados por padres y maestros acerca de la sintomatología negativista desafiante en niños en edad escolar (6-8 años). Además, se pretende analizar si la edad y el sexo del niño afectan el nivel de acuerdo entre informantes. Padres y maestros evaluaron a 702 niños y niñas de 25 escuelas de la Comarca de Osona, Barcelona (España), mediante el Child Sympton Inventory-4 (versión padres y maestros). Los resultados indican una concordancia muy baja, casi nula, entre las valoraciones de ambos informantes; además, las variables edad y sexo de los niños no representan una diferencia significativa en dichas valoraciones. Los padres tienden a evaluar más síntomas del Trastorno Negativista Desafiante como presentes, y a percibir con mayor intensidad su severidad(AU)

Agreement between parents and teachers. The main goal of this study is to determine the degree of agreement between the reports provided by parents and teachers about oppositional defiant symptoms in school children between the ages of 6 and 8 years. In addition, it attempts to determine whether children’s age and sex affect the level of agreement between informants. Parents and teachers assessed 702 girls and boys at 25 schools in the Region of Osona, Barcelona (Spain) with the Child Symptom Inventory-4 (parents’ and teachers' version). The results indicate a very low agreement -practically null-between the valuations of both informants; furthermore, no significant difference due to the variables age and sex of the children was observed in the above-mentioned valuations. The parents tended to appraise most of the symptoms of the Oppositional Defiant Disorder as present and to evaluate their severity as being more intense(AU)

Entrapment of enzymes and carbon nanotubes in biologically synthesized silica: glucose oxidase-catalyzed direct electron transfer.

This work demonstrates a new approach for building bioinorganic interfaces by integrating biologically derived silica with single-walled carbon nanotubes to create a conductive matrix for immobilization of enzymes. Such a strategy not only allows simple integration into biodevices but presents an opportunity to intimately interface an enzyme and manifest direct electron transfer features. Biologically synthesized silica/carbon nanotube/enzyme composites are evaluated electrochemically and characterized by means of X-ray photoelectron spectroscopy. Voltammetry of the composites displayed stable oxidation and reduction peaks at an optimal potential close to that of the FAD/FADH(2) cofactor of immobilized glucose oxidase. The immobilized enzyme is stable for a period of one month and retains catalytic activity for the oxidation of glucose. It is demonstrated that the resulting composite can be successfully integrated into functional bioelectrodes for biosensor and biofuel cell applications.

Oxygen-reducing enzyme cathodes produced from SLAC, a small laccase from Streptomyces coelicolor.

The bacterially-expressed laccase, small laccase (SLAC) of Streptomyces coelicolor, was incorporated into electrodes of both direct electron transfer (DET) and mediated electron transfer (MET) designs for application in biofuel cells. Using the DET design, enzyme redox kinetics were directly observable using cyclic voltammetry, and a redox potential of 0.43 V (SHE) was observed. When mediated by an osmium redox polymer, the oxygen-reducing cathode retained maximum activity at pH 7, producing 1.5 mA/cm2 in a planar configuration at 900 rpm and 40 degrees C, thus outperforming enzyme electrodes produced using laccase from fungal Trametes versicolor (0.2 mA/cm2) under similar conditions. This improvement is directly attributable to differences in the kinetics of SLAC and fungal laccases. Maximum stability of the mediated SLAC electrode was observed at pH above the enzyme's relatively high isoelectric point, where the anionic enzyme molecules could form an electrostatic adduct with the cationic mediator. Porous composite SLAC electrodes with increased surface area produced a current density of 6.25 mA/cm2 at 0.3 V (SHE) under the above conditions.

Riesgo de exposición ocupacional al virus de la hepatitis B en personal de salud venezuelano: estudo multicéntrico / Risk of occupational exposure to hepatitis B virus in Venezuelan health workers: multicenter study

En un estudio multicéntrico fueron recolectadas 970 muestras de suero provenientes de personal trabajador del área de la salud. La presencia de marcadores serológicos del VHB (AgsHB, antisuperficie y anticore total) fue analizada mediante técnica de microELISA. Doscientos cuarenta y siete muestras presentaron uno o más marcadores positivos (27%), siendo el marcador prevalente el antisuperficie cuyo índice de positividad resultó significativo en las diferentes áreas consideradas de menor exposición como medicina interna (24.7%). La proporción de muestras antisuperficie positivas fue además significativamenté superior en el grupo con más de 10 años de labor sanitaria en comparación con la prevalencia demostrada por el grupo con menos de 5 años de servicio (19.1 vs 12.8%). Los grupos considerados con menor riesgo de exposición, contrariamente a lo que podría esperarse, demostraron una prevalencia igual e incluso superior a la demostrada en grupos con exposición contínua o frecuente (17.7 vs 8.6%). Nuestros hallazgos sugieren la permanencia ambiental de carga viral circulante del VHB a nivel intrahospitalario venezuelano