Discharging behavior of confined bipolar electrodes: Coupled electrokinetic and electrochemical dynamics

In this study we numerically investigate the intimately coupled transient electrokinetic and electrochemical dynamics of a nanoconfined bipolar electrode system, using experimental results to guide our analysis. Our recently developed 2D numerical model implements the Poisson-Nernst-Planck-Stokes system of equations to describe nanoscale chemical species transport by advection, migration, and diffusion, as well as the presence of both homogenous and heterogeneous reactions. By eschewing the assumption of electroneutrality and resolving diffuse-charge screening effects, our model uniquely accounts for a wide range of nonlinear transient effects including bipolar electrode (BPE) surface polarization, Faradaic charge accumulation, induced-charge electroosmotic flow, and ion concentration polarization. Using this model, we demonstrate that upon the removal of a polarizing electric field, excess accumulated charge at a BPE surface electrochemically discharges following the capacitive relaxation of diffuse space charge in the electrical double layers (EDLs) surrounding the BPE extremities. These EDLs continue to polarize the BPE as they relax by a process of drift-diffusion, wherein the counter-ionic space charge at each pole promotes a large influx of oppositely charged ions to restore electroneutrality. We numerically reproduced this electrokinetic enhancement effect that was first observed in a recently reported experimental system in which charged fluorophores were used as tracer molecules. Our results also support experimental evidence that, following capacitive EDL relaxation, nanoconfined BPEs can exhibit pseudocapacitance-like discharging behavior that is localized to a single end of the electrode; we experimentally linked this localization to surface oxidation of the anodic BPE pole under the applied field. In addition to providing important insight into the interplay between nanoscale electrokinetic and electrochemical phenomena that govern transient electrode processes, our model and the results presented in this work reinforce the notion that the domain of bipolar electrochemistry constitutes a promising frontier for developing “wirelessly” tunable charge storage and visual detection approaches which exploit both electrokinetic and Faradaic mechanisms

Modeling Faradaic Reactions and Electrokinetic Phenomena at a Nanochannel-Confined Bipolar Electrode

We present the most comprehensive two-dimensional numerical model to date for a nanoconfined bipolar electrochemical system. By accounting for the compact Stern layer and resolving the diffuse part of the electrical double layer at the bipolar electrode (BPE) surface and channel walls, our model captures the impact of surface polarization and ionic charge-screening effects on the heterogeneous charge-transfer kinetics, as well as nonlinear electrokinetic transport phenomena such as induced-charge electroosmosis and concentration polarization. We employ the Poisson-Nernst-Planck and Stokes flow system of equations, unified with generalized Frumkin-Butler-Volmer reaction kinetics, to describe water electrolysis reactions and the resulting transport of ions and dissolved gases in the confined BPE system. Our results demonstrate that under a sufficiently large applied electric field, the rapid reaction kinetics on our Pt BPE dynamically transition from charge-transfer-limited to mass-transfer-limited temporal regimes as regions depleted of redox species form and propagate outward from the respective BPE poles. This phenomenon was visualized experimentally with a pH-sensitive fluorescein dye and showed excellent phenomenological agreement with our numerical calculations, providing a foundation for further understanding and developing bipolar electrochemical processes in confined geometries. We introduce two prospective applications arising from our work: (1) a hybrid hydrodynamic/electrochemical peristaltic pump and (2) deducing information about chemical kinetics through simulation

Single Capsule Bismuth Quadruple Therapy for Eradication of H. pylori Infection: A Real-Life Study

Background and aim: Bismuth quadruple therapy (BQT) or non-bismuth quadruple therapy (i.e., concomitant therapy) (CT) is the first-line regimens to eradicate H. pylori infection in areas with high prevalence of clarithromycin (CLA) resistance. Guidelines suggest that in areas of high prevalence of H. pylori strains with double resistance (i.e., CLA + metronidazole), BQT should be preferred to CT. The aim of this study was to evaluate the efficacy and safety of BQT administered through the three-in-one pill (Pylera) formulation in a large series of H. pylori–infected patients, naive to treatment in a region with high CLA and dual resistance. Patients and methods: We treated 250 patients (148 F and 102 M, mean age 48.6 years) with H. pylori infection naïve to treatment. Patients received esomeprazole 40 mg bid and Pylera 3 tablets qid for 10 days. Diagnosis of H. pylori infection was through 13C urea breath test (13C UBT), or stool antigen test or histology, as appropriate. The evaluation of eradication was through 13C UBT at least 45 days after the end of therapy. Incidence of treatment-related adverse events (TRAEs) was assessed through a questionnaire at the end of treatment. Compliance was considered good if at least 90% of medication had been taken. Statistical analysis was per intention-to-treat e per protocol (PP). 95% confidence intervals (CIs) were calculated. Results: 1) 13 patients (5.2%) discontinued therapy due to side effects; 2) eradication rates in ITT and PP were 227/250 (90.8%; 95% CI 86.3–93.7%) and 226/237 (95.3%; 95% CI 91–99%), respectively; 3) the prevalence of TRAEs was 26.8%; and 4) adherence to treatment was good with compliance greater than 90%. Conclusion: In this real-life study, we demonstrate that in an area with a high prevalence of H. pylori strains with CLA or CLA + metronidazole resistance, BQT using Pylera is an effective therapeutic strategy with ITT eradication rates higher than 90%; this therapy is associated with good compliance and low incidence of side effects

NeQuick 2 total electron content predictions for middle latitudes of North American region during a deep solar minimum

The performance of NeQuick 2 model in computing the vertical total electron content (VTEC) over a wide region placed at middle latitudes of North America during the deep solar minimum that occurred in 2008 has been checked. The long term relationship between EUV irradiance and F10.7 solar flux has changed markedly during the cycle 23/24 minimum with EUV levels decreasing more than expected from F10.7 proxy. A decrease of ionization in the ionosphere could have occurred. Thus, it could be expected that the models overestimate the value of ionospheric parameters for that deep solar minimum. For this study a high density VTEC data grid that covers the Continental United States (CONUS) has been compared with monthly median maps constructed with NeQuick 2. The results show that NeQuick 2 generally gives good predictions for the region which lies between 35°N to 50°N suggesting that nothing exceptional was happening during the 2008 minimum in terms of VTEC NeQuick 2's predictive capabilities. Taking into account that the modeled value is obtained by integration in height of the electron density profile, NeQuick2 would be assuming an inadequate profile for the few highest deviations observed, between 30°N and 35°N. Overall, the model does not give significant overestimation of VTEC as could be expected.Fil: Ezquer, Rodolfo Gerardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Ionosfera; Argentina. Universidad Tecnológica Nacional. Centro de Investigación de Atmósfera Superior y Radiopropagación; ArgentinaFil: Scida, Luis Alberto. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Ionosfera; Argentina. Universidad Tecnológica Nacional. Centro de Investigación de Atmósfera Superior y Radiopropagación; ArgentinaFil: Migoya Orue, Yenca Olivia. The Abdus Salam International Centre for Theoretical Physics; ItaliaFil: Lescano, G. E.. Universidad Tecnológica Nacional. Centro de Investigación de Atmósfera Superior y Radiopropagación; ArgentinaFil: Alazo Cuartas, K.. The Abdus Salam International Centre for Theoretical Physics; ItaliaFil: Cabrera, M.A.. Universidad Tecnológica Nacional. Centro de Investigación de Atmósfera Superior y Radiopropagación; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Electricidad, Electrónica y Computación. Laboratorio de Telecomunicaciones; ArgentinaFil: Radicella, Sandro María. The Abdus Salam International Centre for Theoretical Physics; Itali

Ultrasensitive visual read-out of nucleic acids using electrocatalytic fluid displacement

Diagnosis of disease outside of sophisticated laboratories urgently requires low-cost, user-friendly devices. Disposable, instrument-free testing devices are used for home and physician office testing, but are limited in applicability to a small class of highly abundant analytes. Direct, unambiguous visual read-out is an ideal way to deliver a result on a disposable device; however, existing strategies that deliver appropriate sensitivity produce only subtle colour changes. Here we report a new approach, which we term electrocatalytic fluid displacement, where a molecular binding event is transduced into an electrochemical current, which drives the electrodeposition of a metal catalyst. The catalyst promotes bubble formation that displaces a fluid to reveal a high contrast change. We couple the read-out system to a nanostructured microelectrode and demonstrate direct visual detection of 100 fM DNA in 10 min. This represents the lowest limit of detection of nucleic acids reported using high contrast visual read-out

Processing and mechanical characterization of ZnO/polyester woven carbon-fiber composites with different ZnO concentrations

In this research, processing characterization and mechanical properties of ZnO/polyester woven carbon-fiber composites were investigated. One of our more interesting findings was how the impact energy absorption of woven carbon fibers was affected by the concentrations of ZnO, grown using a hydrothermal process. The impact behavior of ZnO/polyester woven carbon-fiber composites differed according to ZnO concentration during growth. The morphology of damaged surfaces following impact studies was investigated via scanning electron microscopy. Molecular dynamics simulations were performed to calculate the differences in the adhesion energy of the ZnO crystalline structure at the atomistic-level. Additional ZnO increased the mechanical strength of the ZnO/polyester woven carbon-fiber composites, due to the much higher adhesion energy of the side areas of the ZnO crystalline structure. Also, the tensile modulus in composites processed by vacuum-assisted resin-transfer molding exhibited significant enhancement at higher ZnO concentrations.close1