Construction of all-solid-state ion-selective sensors using electrolyte-containing polymers.

All-solid-state NO, K, NH, Na, and Ca ion-selective sensors (ISEs) were prepared using polyvinyl butyral (S-LEC®K KX-5). In the present case, polyvinyl butyral was used as a porous material to keep the internal solution of the respective ISE. All sensors exhibited near-Nernst responses in the concentration region between approximately 10 and 0.

Metagenomic analysis of ready biodegradability tests to ascertain the relationship between microbiota and the biodegradability of test chemicals.

Ready biodegradability tests conducted in accordance with the Organisation for Economic Co-operation and Development guidelines (test 301C or test 301F) are performed using activated sludge (AS) prepared by the Chemicals Evaluation and Research Institute (AS-CERI) or that taken from a sewage treatment plant (AS-STP). It had been reported that AS-CERI had lower activity than AS-STP in biodegrading test chemicals, and that biodegradation was accelerated by increasing the volume of the test medium. However, these phenomena have not been clarified from the perspective of the microbiota.

Influence of distal glycan mimics on direct electron transfer performance for bilirubin oxidase bioelectrocatalysts.

Bilirubin oxidase (BOD) is a bioelectrocatalyst that reduces dioxygen (O) to water and is capable of direct electron transfer (DET)-type bioelectrocatalysis via its electrode-active site (T1 Cu). BOD from Myrothecium verrucaria (mBOD) has been widely studied and has strong DET activity. mBOD contains two N-linked glycans (N-glycans) with N472 and N482 binding sites distal to T1 Cu.

Directional propagation of action potential within a single cell and intercellular conduction within a cell aggregate using model cell systems.

The mechanism of directional propagation of action potential throughout a single cell was examined using a liquid-membrane model cell system. In the experiments on the liquid-membrane model cell system, liquid-membrane cells were constructed to mimic the function of K and voltage-gated Na channels, which play important roles in action potential propagation. These channel-mimicking cells were connected electrically, and a model cell system was composed of four parts within the one cell.

Effects of N-linked glycans of bilirubin oxidase on direct electron transfer-type bioelectrocatalysis.

Bilirubin oxidase from Myrothecium verrucaria (mBOD) is a promising enzyme for catalyzing the four-electron reduction of dioxygen into water and realizes direct electron transfer (DET)-type bioelectrocatalysis. It has two N-linked glycans (N-glycans), and N472 and N482 are known as binding sites. Both binding sites located on opposite side of the type I (T1) Cu, which is the electrode-active site of BOD.

Multiple electron transfer pathways of tungsten-containing formate dehydrogenase in direct electron transfer-type bioelectrocatalysis.

Tungsten-containing formate dehydrogenase from AM1 (FoDH1)-a promising biocatalyst for the interconversion of carbon dioxide/formate and nicotine adenine dinucleotide (NAD)/NADH redox couples-was investigated using structural biology and bioelectrochemistry. FoDH1 is reported to be an enzyme that can realize "direct electron transfer (DET)-type bioelectrocatalysis." However, its 3-D structure, electrode-active sites, and electron transfer (ET) pathways remain unclear.

Inhibition of direct-electron-transfer-type bioelectrocatalysis of bilirubin oxidase by silver ions.

In enzyme-based biosensors, Ag eluted from the reference electrode inhibits the enzyme activity. Herein, to suppress the inhibition of bilirubin oxidase (BOD) by Ag, kinetic analysis was used to examine the effect of Ag on the activity of BOD. It was confirmed that the addition of Ag decreased the bioelectrocatalytic activity of BOD.

Ion transport across bilayer lipid membranes in the presence of tetraphenylborate.

A pair of symmetrical cathodic and anodic peaks is observed in cyclic voltammograms for the ion transport across a bilayer lipid membrane (BLM) between two aqueous phases in the presence of tetraphenylborate (TPhB). Although TPhB serves as a carrier of a hydrophilic counter ion (Na) under the steady-state condition, the reason for the appearance of symmetrical peaks has not been clearly explained until now. From the chronoamperometric analysis, it is turned out that the symmetrical peaks are attributed to the translocation of TPhB between two adsorbed layers on the surface of the BLM.

Comprehensive understanding of multiple actions of anticancer drug tamoxifen in isolated mitochondria.

Tamoxifen has been widely used in the treatment of estrogen receptor (ER)-positive breast cancer, whereas it also exhibits ER-independent anticancer effects in various cancer cell types. As one of the convincing mechanisms underlying the ER-independent effects, induction of apoptosis through mitochondrial dysfunction has been advocated. However, the mechanism of action of tamoxifen even at the isolated mitochondrial level is not fully understood and remains controversial.

Cyanide sensitivity in direct electron transfer-type bioelectrocatalysis by membrane-bound alcohol dehydrogenase from Gluconobacter oxydans.

An overexpression system of membrane-bound alcohol dehydrogenase (ADH) from Gluconobacter oxydans was constructed to examine its bioelectrocatalytic characteristics. The effects of cyanide (CN) addition on the kinetics of direct electron transfer (DET)-type bioelectrocatalysis by ADH were analyzed. CN enhanced the bioelectrocatalytic activity, while the catalytic activity in the solution remained unchanged, even in the presence of CN.

Pollution Control of Nitrate-selective Membrane by the Inner Solution and On-site Monitoring of Nitrate Concentration in Soil.

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 NO-selective electrode displayed a linear response to the concentration of NO with a Nernstian slope of -53 ± 1 mV decade, in the concentration region between 10 and 2 mol dm (M). The NO detection limit was about 10 M.

Electrical cell-to-cell communication using aggregates of model cells.

Cell-to-cell communication via a local current caused by ion transport is elucidated using a model-cell system. To imitate tissues such as smooth muscles and cardiac muscles, liquid-membrane cells mimicking the function of K+ and Na+ channels were made. Connecting these channel-mimicking cells (K+ channel and voltage-gated Na+ channel) in parallel, model cells imitating living cell functions were constructed.

Development Perspective of Bioelectrocatalysis-Based Biosensors.

Bioelectrocatalysis provides the intrinsic catalytic functions of redox enzymes to nonspecific electrode reactions and is the most important and basic concept for electrochemical biosensors. This review starts by describing fundamental characteristics of bioelectrocatalytic reactions in mediated and direct electron transfer types from a theoretical viewpoint and summarizes amperometric biosensors based on multi-enzymatic cascades and for multianalyte detection. The review also introduces prospective aspects of two new concepts of biosensors: mass-transfer-controlled (pseudo)steady-state amperometry at microelectrodes with enhanced enzymatic activity without calibration curves and potentiometric coulometry at enzyme/mediator-immobilized biosensors for absolute determination.

Automatic Management of Nutrient Solution for Hydroponics-Construction of Multi-ion Stat.

In order to improve plant factories, an appropriate control system on fertilization is urgently required. An automatic management system to control nutrient concentration was constructed using a programmable logic controller (PLC) and ion selective electrodes (ISEs) of nitrate, phosphate, and potassium ion. The concentration of nutrient components in a culture solution was monitored using these ISEs.

Direct electron transfer-type bioelectrocatalysis of FAD-dependent glucose dehydrogenase using porous gold electrodes and enzymatically implanted platinum nanoclusters.

The direct electron transfer (DET)-type bioelectrocatalysis of flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (GDH) from Aspergillus terreus (AtGDH) was carried out using porous gold (Au) electrodes and enzymatically implanted platinum nanoclusters (PtNCs). The porous Au electrodes were prepared by anodization of planar Au electrodes in a phosphate buffer containing glucose as a reductant. Moreover, PtNCs were generated into AtGDH by an enzymatic reduction of hexachloroplatinate (IV) ion.

Fabrication of a Phosphate Ion Selective Electrode Based on Modified Molybdenum Metal.

A phosphate ion-selective electrode using molybdenum metal was constructed. The modified molybdenum electrode responded to HPO in the presence of molybdenum dioxide and molybdophosphate (PMoO) on the surface. The electrode exhibited a linear response to HPO in the concentration range between 1.

Bioelectrocatalytic performance of d-fructose dehydrogenase.

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 origin of hyperpolarization based on the directional conduction of action potential using a model nerve cell system.

In nerve cells, changes in local membrane potentials are generated and propagated along a nerve axon mainly by the function of K and Na channels. Generally, concurrent monitoring of multi-points on an axon is performed based on the voltage-clamp method. As the respective membrane potentials have been evaluated by considering the relations between the applied potential, the local current, and conductance, experimental values are not directly evaluated.

Construction of an Automatic Nutrient Solution Management System for Hydroponics-Adjustment of the K-Concentration and Volume of Water.

An automatic management system for nutrient solutions was constructed using a programmable logic controller (PLC) and a K-ion selective electrode (K-ISE). The concentration of K was monitored by the K-ISE. When the concentration of K fell to the threshold limit, an appropriate amount of a concentrated K solution was added to the hydroponic solution.

Construction of Nitrate-selective Electrodes and Monitoring of Nitrates in Hydroponic Solutions.

A liquid-membrane type nitrate-selective electrode was constructed, in which the responding membrane contained polyvinylchloride, o-nitrophenyloctylether and tetraheptylammonium nitrate. The NO-selective electrode displayed a linear response to the concentration of NO with a Nernstian slope of -53.3 ± 1.

Nanostructured Porous Electrodes by the Anodization of Gold for an Application as Scaffolds in Direct-electron-transfer-type Bioelectrocatalysis.

In this study, nanostructured porous gold electrodes were prepared by the anodization of gold in the presence of oxalic acid or glucose as a reductant, and applied as scaffolds for direct electron transfer (DET)-type bioelectrocatalysis. Gold cations generated in the anodization seem to be reduced by the reductant to construct a porous gold structure. The DET-type performance of the electrode was examined using two DET-type model enzymes, bilirubin oxidase (BOD) and peroxidase (POD), for the four-electron reduction of dioxygen and the two-electron reduction of peroxide, respectively.

Carbon-nanotube-caged microbial electrodes for bioelectrocatalysis.

A method to stably immobilize microbes on electrodes was developed. Resting cells of Methylobacterium extorquens AM1(MeAM1) were caged within multiwalled carbon nanotubes (MWNTs)by adding the cells to a water dispersion of MWNTs then allowing the resulting mixture to dry on electrodes. The MeAM1-MWCNTs electrode thus obtained displayed excellent activities in the bidirectional bioelectrocatalysis due to formate dehydrogenase(s) in the resting cells; formate oxidation and carbon dioxide reduction proceeded at steady-state catalytic current densities of 0.

Electrochemical Study on the Extracellular Electron Transfer Pathway from Shewanella Strain Hac319 to Electrodes.

Shewanella can transfer electrons to various extracellular electron acceptors. We electrochemically investigated the pathway of extracellular electron transfer from Shewanella strain Hac319 to electrodes. A resting cell suspension of Shewanella strain Hac319 containing lactate produced a steady-state sigmoidal wave in the presence of flavin mononucleotide (FMN) in cyclic voltammetry, but not in the absence of FMN.

Simultaneous Detection of Lactate Enantiomers Based on Diffusion-controlled Bioelectrocatalysis.

Amperometric biosensors were constructed for the simultaneous detection of lactate enantiomers. The enantioselectivity of the sensor is based on NAD-dependent l- and d-lactate dehydrogenases that, respectively, oxidize l- and d-lactates into pyruvate. The NADH formed during the enzymatic reduction was catalytically oxidized at Meldola's blue-adsorbed mesoporous electrodes.