SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Electrochemical cell

217

We have developed an implantable fuel cell that generates power through glucose oxidation, producing 3.4 μW cm(-2) steady-state power and up to 180 μW cm(-2) peak power. The fuel cell is manufactured using a novel approach, employing semiconductor fabrication techniques, and is therefore well suited for manufacture together with integrated circuits on a single silicon wafer. Thus, it can help enable implantable microelectronic systems with long-lifetime power sources that harvest energy from their surrounds. The fuel reactions are mediated by robust, solid state catalysts. Glucose is oxidized at the nanostructured surface of an activated platinum anode. Oxygen is reduced to water at the surface of a self-assembled network of single-walled carbon nanotubes, embedded in a Nafion film that forms the cathode and is exposed to the biological environment. The catalytic electrodes are separated by a Nafion membrane. The availability of fuel cell reactants, oxygen and glucose, only as a mixture in the physiologic environment, has traditionally posed a design challenge: Net current production requires oxidation and reduction to occur separately and selectively at the anode and cathode, respectively, to prevent electrochemical short circuits. Our fuel cell is configured in a half-open geometry that shields the anode while exposing the cathode, resulting in an oxygen gradient that strongly favors oxygen reduction at the cathode. Glucose reaches the shielded anode by diffusing through the nanotube mesh, which does not catalyze glucose oxidation, and the Nafion layers, which are permeable to small neutral and cationic species. We demonstrate computationally that the natural recirculation of cerebrospinal fluid around the human brain theoretically permits glucose energy harvesting at a rate on the order of at least 1 mW with no adverse physiologic effects. Low-power brain-machine interfaces can thus potentially benefit from having their implanted units powered or recharged by glucose fuel cells.

Concepts: Carbon dioxide, Enzyme, Hydrogen, Redox, Electrochemistry, Carbon, Electrochemical cell, Electrolysis

186

ABSTRACT Fe(II)-oxidizing aerobic bacteria are poorly understood, due in part to the difficulties involved in laboratory cultivation. Specific challenges include (i) providing a steady supply of electrons as Fe(II) while (ii) managing rapid formation of insoluble Fe(III) oxide precipitates and (iii) maintaining oxygen concentrations in the micromolar range to minimize abiotic Fe(II) oxidation. Electrochemical approaches offer an opportunity to study bacteria that require problematic electron donors or acceptors in their respiration. In the case of Fe(II)-oxidizing bacteria, if the electron transport machinery is able to oxidize metals at the outer cell surface, electrodes poised at potentials near those of natural substrates could serve as electron donors, eliminating concentration issues, side reactions, and mineral end products associated with metal oxidation. To test this hypothesis, the marine isolate Mariprofundus ferrooxydans PV-1, a neutrophilic obligate Fe(II)-oxidizing autotroph, was cultured using a poised electrode as the sole energy source. When cells grown in Fe(II)-containing medium were transferred into a three-electrode electrochemical cell, a cathodic (negative) current representing electron uptake by bacteria was detected, and it increased over a period of weeks. Cultures scraped from a portion of the electrode and transferred into sterile reactors consumed electrons at a similar rate. After three transfers in the absence of Fe(II), electrode-grown biofilms were studied to determine the relationship between donor redox potential and respiration rate. Electron microscopy revealed that under these conditions, M. ferrooxydans PV-1 attaches to electrodes and does not produce characteristic iron oxide stalks but still appears to exhibit bifurcate cell division. IMPORTANCE Electrochemical cultivation, supporting growth of bacteria with a constant supply of electron donors or acceptors, is a promising tool for studying lithotrophic species in the laboratory. Major pitfalls present in standard cultivation methods used for metal-oxidizing microbes can be avoided by the use of an electrode as the sole electron donor. Electrochemical cultivation also offers a window into the poorly understood metabolism of microbes such as obligate Fe(II), Mn(II), or S(0) oxidizers by replacing the electron source with the controlled surface of an electrode. The elucidation of redox-dependent behavior of these microbes could enhance industrial applications tuned to oxidation of specific metals, provide insight into how bacteria evolved to compete with oxygen for reactive metal species, and model geochemical impacts of their metabolism in the environment.

Concepts: Photosynthesis, Bacteria, Redox, Electrochemistry, Cellular respiration, Electrode, Electrochemical cell, Electrolysis

149

Collisions of excitation pulses in dissipative systems lead usually to their annihilation. In this paper, we report electrochemical experiments exhibiting more complex pulse interaction with collision survival and pulse splitting, phenomena that have rarely been observed experimentally and are only poorly understood theoretically. Using spatially resolved in-situ Fourier transform infrared spectroscopy (FTIR) in the attenuated total reflection configuration, we monitored reaction pulses during the electrochemical oxidation of CO on Pt thin film electrodes in a flow cell. The system forms quasi-1d pulses that align parallel to the flow and propagate perpendicular to it. The pulses split once in a while, generating a second solitary wave in the backward moving direction. Upon collision, the waves penetrate each other in a soliton-like manner. These unusual pulse dynamics could be reproduced with a 3-component reaction-diffusion-migration model with two inhibitor species, one of them exhibiting a long-range spatial coupling. The simulations shed light on existence criteria of such dissipative solitons.

Concepts: Spectroscopy, Light, Refraction, Electrochemistry, Fourier transform, Electrochemical cell, Infrared spectroscopy, Fourier transform spectroscopy

44

Extensive evidence has shown that long-range charge transport can occur along double helical DNA, but active control (switching) of single-DNA conductance with an external field has not yet been demonstrated. Here we demonstrate conductance switching in DNA by replacing a DNA base with a redox group. By applying an electrochemical (EC) gate voltage to the molecule, we switch the redox group between the oxidized and reduced states, leading to reversible switching of the DNA conductance between two discrete levels. We further show that monitoring the individual conductance switching allows the study of redox reaction kinetics and thermodynamics at single molecular level using DNA as a probe. Our theoretical calculations suggest that the switch is due to the change in the energy level alignment of the redox states relative to the Fermi level of the electrodes.

Concepts: DNA, Hydrogen, Redox, Electrochemistry, Nitrogen, Radical, Electrochemical cell, Electrolysis

34

Objective. Hypertension is the largest threat to patient health and a burden to health care systems. Despite various options, 30% of patients do not respond sufficiently to medical treatment. Mechanoreceptors in the aortic arch relay blood pressure (BP) levels through vagal nerve (VN) fibers to the brainstem and trigger the baroreflex, lowering the BP. Selective electrical stimulation of these nerve fibers reduced BP in rats. However, there is no technique described to localize and stimulate these fibers inside the VN without inadvertent stimulation of non-baroreceptive fibers causing side effects like bradycardia and bradypnea. Approach. We present a novel method for selective VN stimulation to reduce BP without the aforementioned side effects. Baroreceptor compound activity of rat VN (n = 5) was localized using a multichannel cuff electrode, true tripolar recording and a coherent averaging algorithm triggered by BP or electrocardiogram. Main results. Tripolar stimulation over electrodes near the barofibers reduced the BP without triggering significant bradycardia and bradypnea. The BP drop was adjusted to 60% of the initial value by varying the stimulation pulse width and duration, and lasted up to five times longer than the stimulation. Significance. The presented method is robust to impedance changes, independent of the electrode’s relative position, does not compromise the nerve and can run on implantable, ultra-low power signal processors.

Concepts: Medicine, Electrochemistry, Vagus nerve, Carotid sinus, Vagus nerve stimulation, Electrochemical cell, Hypotension, Baroreflex

28

Raman spectra and images of a living L929 (NCTC) cell have been measured with 532 nm excitation. Both reduced and oxidized forms of cytochromes b and c (cyt b and cyt c) have been observed in situ without any pretreatment. The redox states of cyts b and c have been assessed quantitatively with a spectral analysis. It has been found that reduced cyt c is more abundant than oxidized cyt c, while oxidized cyt b is slightly more abundant than reduced cyt b in a living cell. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

Concepts: Scientific method, Adenosine triphosphate, Enzyme, Iron, Redox, Electrochemistry, Cellular respiration, Electrochemical cell

28

Replacing precious and nondurable Pt catalysts with cheap and commercially available materials to facilitate sluggish cathodic oxygen reduction reaction (ORR) is a key issue in the development of fuel cell technology. The recently developed cost effective and highly stable metal-free catalysts reveal comparable catalytic activity and significantly better fuel tolerance than that of current Pt-based catalysts; therefore, they can serve as feasible Pt alternatives for the next generation of ORR electrocatalysts. Their promising electrocatalytic properties and acceptable costs greatly promote the R&D of fuel cell technology. This review provides an overview of recent advances in state-of-the-art nanostructured metal-free electrocatalysts including nitrogen-doped carbons, graphitic-carbon nitride (g-C(3) N(4) )-based hybrids, and 2D graphene-based materials. A special emphasis is placed on the molecular design of these electrocatalysts, origin of their electrochemical reactivity, and ORR pathways. Finally, some perspectives are highlighted on the development of more efficient ORR electrocatalysts featuring high stability, low cost, and enhanced performance, which are the key factors to accelerate the commercialization of fuel cell technology.

Concepts: Enzyme, Hydrogen, Redox, Electrochemistry, Nitrogen, Carbon, Electrochemical cell, Electrolysis

28

Chitosan-ferrocene (CHIT-Fc) hybrid was synthesized through covalent modification and its electrochemical properties in immobilized form were studied by using cyclic voltammetry. The hybrid film exhibited reversible electrochemistry with a formal potential of +0.35 V (vs. Ag/AgCl) at pH 5.5. The Fc in CHIT matrix retained its electrocatalytic activity and did not diffuse from the matrix. This redox-active hybrid was further employed as a support for immobilization of glucose oxidase (GOx) and whole cells of Gluconobacter oxydans using glutaraldehyde on a glassy carbon electrode (GCE). The experimental conditions were optimized and the analytical characteristics of enzyme and microbial biosensors were evaluated for glucose in flow injection analysis (FIA) system. Under optimized conditions, both enzyme and microbial biosensors exhibited wide linear ranges for glucose from 2.0 to 16.0 mM and from 1.5 to 25.0 mM, respectively. Moreover, the biosensors have the advantages of relatively fast response times, good reproducibility and stability in FI mode. It was demonstrated that CHIT-Fc provides a biocompatible microenvironment for both bioctalysts and an electron transfer pathway. Additionally, integration of the enzyme and microbial biosensors into the FIA system has several advantages including capability of automation and high throughput at low cost. This promising redox hybrid can be utilized as an immobilization matrix for biomolecules in biosensor systems.

Concepts: Electron, Enzyme, Redox, Electrochemistry, Carbon, Electrochemical cell, Biosensor, Glucose oxidase

28

A facile and green method was developed to synthesize the graphene-carbon nanotubes (Gr-CNTs) nanocomposite with a sandwich lamination structure. Pt nanoparticles were loaded on the as-synthesized Gr-CNTs nanocomposite to prepare an electrochemical sensor for determining bisphenol A (BPA) in thermal printing paper. The electrochemical behavior of BPA on the Pt/Gr-CNTs nanocomposite was investigated by cyclic voltammetry (CV) and chronocoulometry (CC). The direct determination of BPA was accomplished by using differential pulse voltammetry (DPV) under optimized conditions. The oxidation peak current was proportional to the BPA concentration in the range from 6.0 × 10(-8) to 1.0 × 10(-5) M and 1.0 × 10(-5) to 8.0 × 10(-5) M with a correlation coefficient of 0.987 and 0.998, respectively. The detection limit was 4.2 × 10(-8) M (S/N = 3). The fabricated electrode showed good reproducibility, stability and selectivity. The proposed method was successfully applied to determine BPA in thermal printing papers samples and the results were satisfactory.

Concepts: Electrochemistry, Bisphenol A, Analytical chemistry, Electrochemical cell, Paper, Endocrine disruptor, Voltammetry, Differential pulse voltammetry

27

We propose the very first “Nernstian biosupercapacitor”, a biodevice based on only one redox polymer: poly(vinyl imidazole-co-allylamine)[Os(bpy)2 Cl], and two biocatalysts. At the bioanode PQQ-dependent glucose dehydrogenase reduces the Os(3+) moieties at the polymer to Os(2+) shifting the Nernst potential of the Os(3+) /Os(2+) redox couple to negative values. Concomitantly, at the biocathode the reduction of O2 by means of bilirubin oxidase embedded in the same redox polymer leads to the oxidation of Os(2+) to Os(3+) shifting the Nernst potential to higher values. Despite the use of just one redox polymer an open circuit voltage of more than 0.45 V was obtained during charging and the charge is stored in the redox polymer at both the bioanode and the biocathode. By connecting both electrodes via a predefined resistor a high power density is obtained for a short time exceeding the steady state power of a corresponding biofuel cell by a factor of 8.

Concepts: Adenosine triphosphate, Enzyme, Glucose, Redox, Electrochemistry, Nicotinamide adenine dinucleotide, Electrochemical cell, Steady state