Phosphorous is one of three major nutritional elements for plants and usually exists as phosphate ions in nature. For hydroponic culturing and wastewater treatment, the development of a ...high-performance phosphate sensor would be very helpful. A novel phosphate ion-selective electrode was constructed using a cobalt phosphate surface coated cobalt electrode. The potential response seems to be caused by the formation of Co(H2PO4)2 in the coexistence of CoO and Co(OH)2. The sensor exhibited a linear response to H2PO4− in the concentration range from 1.0 × 10−5 to 1.0 × 10−1 mol L−1 at a pH range from 4.0 to 6.5 with a slope of −39 mV dec−1. The sensor was unaffected by common anions, such as chloride, carbonate, and sulfate. The electrode maintained stability for at least 4 weeks in a live hydroponics system when sufficient Co3(PO4)2·8H2O was deposited on the Co electrode.
A phosphate ion selective electrode coated with cobalt phosphate hydrate was produced. This electrode responds to the activity of H2PO4−, and it exhibited a linear response to H2PO4− in the concentration range from 1.0 × 10−5 to 1.0 × 10−1 mol dm‒3 at a pH range from 4 to 7 with a slope of −39 mV dec−1. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
The electric organ of a typical electric fish was artificially constructed by use of a model-cell system combining liquid-membrane cells mimicking the function of K+ and voltage-gated Na+ channels. ...The relation between the power generation of the electric organ and the rapid synchronization was investigated using the external electric stimulus. As for a model electrocyte, only a K+-channel-mimicking cell was set on the head side and both K+-channel and voltage-gated Na+-channel mimicking cells were placed on the caudal side. The potential difference between one and another side through the electrocyte changed from 0 V to about 0.15 V after the external electric stimulus was applied. In the firing state, the electric current due to the transfer of K+ and Na+ flowed through the model electrocyte. When multiple model electrocytes were in series, the simultaneous ignitions by opening of voltage-gated Na+ channels generate a large voltage through the electrocyte aggregates. In this case, the total voltage was the sum of the potential differences of the respective electrocytes. When several model electrocytes were in parallel, the total current was the sum of the currents of all electrocytes. The rapid synchronization of the electric organ of the electric eel (0.5 ms level) seems to be caused by circulating leak currents among neighboring cells through neural and vascular networks.
Diffusion-controlled amperometric biosensors for dissolved oxygen (O2) were constructed by immobilization of multi-copper oxidases (copper efflux oxidase and bilirubin oxidase) on porous gold ...microdisk electrodes fabricated by anodization in a glucose solution. The immobilized enzymes rapidly consumed O2 near the electrode at potentials more negative than 0.2 V vs. Ag|AgCl|sat. KCl via direct electron transfer-type bioelectrocatalysis and the reduction current reached the steady state limiting value under static conditions. The fabricated biosensor exhibited a linear response to dissolved O2 concentration and was almost identical to the theoretical sensor, based on nonlinear diffusion of O2 around the microdisk electrode. The biosensor response was fast enough to monitor the catalytic consumption of dissolved O2 by glucose oxidase and exhibited storage stability for more than six days.
•Porous structures on a gold surface enhance the bioelectrocatalytic activity of multi-copper oxidases.•Diffusion-controlled biocatalytic oxygen reduction occurs at microelectrodes.•Oxygen biosensors operate without calibration.•Biosensors function under neutral and weakly acidic conditions.•Response of the biosensor is fast enough to monitor oxidase reactions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
In nerve cells, the concurrent monitoring of multipoint on the axon has been conducted based on the voltage‐clamp method using two long parallel electrodes inside and outside the axon. As the ...respective membrane potentials have been evaluated by considering the clamping potential, the local current, and the conductance, the membrane potentials were not actually evaluated. We directly measured the actual membrane potentials and local currents of the respective cells using a nerve‐model‐system comprising some liquid‐membrane cells. It is proved that the action potential propagation is artificially facilitated or prevented by both the external electric generator and two long electrodes.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Porous gold (Au) electrodes prepared by anodization of Au electrodes in buffer solutions containing glucose were utilized as scaffolds for direct electron transfer (DET)-type bioelectrocatalysis of ...bilirubin oxidase (BOD). The three-dimensional porous structure appeared to promote DET-type bioelectrocatalysis of BOD. The current density of DET-type bioelectrocatalysis of BOD increased with the formation of a three-dimensional porous structure at the beginning of anodization; however, it showed saturation characteristics with a further increase in the non-Faradaic current. Moreover, the glucose concentration during anodization affected the activity of DET-type bioelectrocatalysis of BOD. Scanning electron microscopy of the prepared porous Au electrodes showed that the structure of the electrode surface depended on the glucose concentration. Achieving a pore size distribution suitable for substrate transport and enzyme orientation seemed to be dependent on the glucose concentration.
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•Anodization of gold electrodes in glucose solutions provides the porous structure.•The surface structure is affected by the glucose concentration during anodization.•Porous gold electrodes are effective scaffolds for bioelectrocatalysis.•Bioelectrocatalysis of bilirubin oxidase depends on the porous structure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
A liquid-membrane type nitrate-selective electrode was improved to lower the influence of contaminants by modifying its inner electrode system from Ag | AgCl | Cl− to Ag | Ag+. The NO3−-selective ...electrode displayed a linear response to the concentration of NO3− with a Nernstian slope of –53 ± 1 mV decade−1, in the concentration region between 10−5 and 2 mol dm−3 (M). The NO3− detection limit was about 10−5 M. The electrochemical response of this electrode was stable for more than 30 days. The deterioration in responding characteristics due to the coexistence of Cl− was suppressed by use of the Ag | Ag+ redox couple in the absence of Cl− inside the NO3−-selective electrode.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Ketjen Black (KB), a mesoporous carbon material, was modified with gold nanoparticles (AuNPs) and 4-mercaptobenzoic acid (MBA). The MBA/AuNP-modified KB was utilized as an effective scaffold for the ...direct electron transfer (DET)-type bioelectrocatalytic reduction of dioxygen by bilirubin oxidase from Myrothecium verrucaria (BOD). Owing to the MBA/AuNP modification, the limiting current density of the steady-state catalytic wave was doubled and the half-wave potential of the catalytic wave was shifted to the positive direction by 140mV. The kinetic analysis of the steady-state catalytic wave indicated that the modification narrowed the orientation distribution of the adsorbed BOD and shortened the mean length between the redox copper site of BOD and the electrode surface. The electrostatic attraction and π–π interactions between BOD and MBA are likely responsible for the favorable orientation of the enzyme.
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•Ketjen Black was modified with 4-mercaptobenzoic acid and AuNPs.•Modified electrode was an effective scaffold for DET-type bioelectrocatalysis of BOD.•Half-wave potential of the catalytic wave was close to the formal potential of BOD.•Kinetic analysis of the wave provided information about the orientation of BOD.•BOD seemingly adsorbed in homogeneous and productive orientations on the electrode.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
This review summarizes the bioelectrocatalytic properties of d-fructose dehydrogenase (FDH), while taking into consideration its enzymatic characteristics. FDH is a membrane-bound flavohemo-protein ...with a molecular mass of 138 kDa, and it catalyzes the oxidation of d-fructose to 5-keto-d-fructose. The characteristic feature of FDH is its strong direct-electron-transfer (DET)-type bioelectrocatalytic activity. The pathway of the DET-type reaction is discussed. An overview of the application of FDH-based bioelectrocatalysis to biosensors and biofuel cells is also presented, and the benefits and problems associated with it are extensively discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
A high-power mediated electron transfer type formate (HCOO–)/dioxygen (O2) biofuel cell is reported herein. The cell utilizes a Ketjen Black modified waterproof carbon cloth as the electrode ...material. The bioanode comprises tungsten-containing formate dehydrogenase and a viologen-functionalized polymer, whereas the biocathode comprises bilirubin oxidase and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate). In addition, a gas diffusion type system was employed for the biocathode to realize a high-speed O2 supply. These electrodes exhibited a large current density of 20 mA cm–2 in the quiescent steady state for both HCOO– oxidation and O2 reduction. Finally, these electrodes were coupled to construct an HCOO–/O2 biofuel cell without a separator. The cell exhibited a maximum power density of 12 mW cm–2 at a cell voltage of 0.78 V under quiescent conditions and an open-circuit voltage of 1.2 V. We show the great potential of HCOO– for the fuel of biofuel cells.
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IJS, KILJ, NUK, PNG, UL, UM
“Cyclic voltammetry” is one of the most common electrochemical techniques, not only for electrochemists but also for researchers in other fields. However, the principles of cyclic voltammetry are ...very complex; beginners and even experts may struggle with their application. Therefore, we explain the fundamental principles in Part 1 and introduce the practical issues associated with recent trends such as fuel cells, capacitors, and sensors in Part 2. In this comprehensive paper, we focus on the electrochemical reversibility in cyclic voltammograms classified as reversible, quasi-reversible, and irreversible processes, which are useful for obtaining information on the reaction rates of electrodes. We also explain the relevant basic principles, experimental setup, and ideas of background current.
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