Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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Study of carbon dioxide electrochemical reduction in flow cell system using copper modified boron-doped diamond

Zahran Ilyasa S., Krisma Jiwanti P., Khalil M., Einaga Y., Anggraningrum Ivandini T.

E3S Web of Conferences (E3S Web of Conferences) 211 2020.11

ISSN 25550403

High concentrations of CO2 in the atmosphere may cause climate and environmental changes. Therefore, various research has been extensively performed to reduce CO2 by converting CO2 directly into hydrocarbons. In this research, CO2 electrochemical reduction was studied using boron-doped diamond (BDD) modified with copper nanoparticles to improve BDD electrodes' catalytic properties. The deposition was performed by chronoamperometry technique at a potential of -0.6 V (vs. Ag/AgCl) and characterized using SEM, EDS, XPS, and cyclic voltammetry (CV). CO2 electrochemical reduction on BDD and Cu-BDD was carried out at -1.5 V (vs. Ag/AgCl) for 60 minutes. The products were analyzed using HPLC and GC. The product was mainly formic acid with a concentration of 11.33 mg/L and 33% faradaic efficiency on a Cu-BDD electrode.

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In Vivo Real-Time Simultaneous Examination of Drug Kinetics at Two Separate Locations Using Boron-Doped Diamond Microelectrodes

Hanawa A., Ogata G., Sawamura S., Asai K., Kanzaki S., Hibino H., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 92 ( 20 ) 13742 - 13749 2020.10

ISSN 00032700

Methylcobalamin, which is used for the clinical treatment of patients with neuropathy, can have an impact on the sensorineural components associated with the cochlea, and it is possible that the auditory threshold in a certain population of patients with deafness may be recovered. Nonetheless, it remains uncertain whether the action site of methylcobalamin is localized inside or outside the cochlea and which cellular or tissue element is targeted by the drug. In the present work, we developed a method to realize in vivo real-time simultaneous examination of the drug kinetics in two separate locations using boron-doped diamond microelectrodes. First, the analytical performance of methylcobalamin was studied and the measurement protocol was optimized in vitro. Then, the optimized protocol was applied to carry out real-time measurements inside the cochlea and the leg muscle in live guinea pigs while systemically administering methylcobalamin. The results showed that the methylcobalamin concentration in the cochlea was below the limit of detection for the microelectrodes or the drug did not reach the cochlea, whereas the compound clearly reached the leg muscle.

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Study of nitrate contaminants removal from groundwater on copper modified BDD electrode

Kuang P., Cui Y., Feng C., Einaga Y.

E3S Web of Conferences (E3S Web of Conferences) 194 2020.10

ISSN 25550403

The electrochemical nitrate reduction by using boron-doped diamond (BDD) and copper modified boron-doped diamond (Cu-BDD) electrodes was investigated at various potentials. Nitrate reduction efficiency and the products distribution was strongly dependent on the applied potential for both electrodes. The highest nitrate reduction efficiency of 77% was obtained at -2.0 V (vs. Ag/AgCl) by using Cu-BDD. Compared with BDD electrode, nitrate reduction on Cu-BDD electrode occurred at more positive potential. Copper oxides formed on BDD surface efficiently promoted enhanced conductivity of electrode to promote electrons transfer during nitrate reduction process. Meanwhile, the catalytic ability of copper was also conductive to the nitrate transformation. Therefore, the developed Cu-BDD would be a promising approach for efficient nitrate removal from groundwater.

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Oxidation reaction of dissolved hydrogen sulfide using boron doped diamond

Triana Y., Tomisaki M., Einaga Y.

Journal of Electroanalytical Chemistry (Journal of Electroanalytical Chemistry) 873 2020.09

ISSN 15726657

© 2020 Elsevier B.V. We studied an oxidation reaction of dissolved hydrogen sulfide using boron doped diamond (BDD) electrodes and 0.1 mol Lˉ1 KClO4 as an electrolyte. Oxidation of H2S and HSˉ started at potentials of +1.7 V and + 0.5 V (vs. Ag/AgCl), respectively. In order to study the oxidation behavior, the effects of pH and the scan rate were investigated. Moreover, as demonstrated by X-ray photoelectron spectroscopy, no sulfur fouling was detected on the BDD surface. A linear calibration curve was observed in the concentration range of 0.08–2.34 mg Lˉ1 (r2 = 0.99) with a detection limit of 0.82 μg Lˉ1 (S/N = 3). In addition, an interference test with CO2 was performed, which showed there was no significant interference to the sensor.

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Weak Antilocalization and Spin Hall Effect in Pt Films Doped with Molecular Spin

Iwamoto W., Yamamoto T., Tsuchii K., Tazaki Y., Asami A., Hayashi H., Einaga Y., Ando K.

ACS Applied Electronic Materials (ACS Applied Electronic Materials) 2 ( 7 ) 2098 - 2103 2020.07

© 2020 American Chemical Society. A high degree of tunability and versatility of organic chemistry has paved the way toward molecular engineering of electronic and spintronic devices. Here, we report molecular spin doping of a Pt film, the key material in spin orbitronics. The molecular spin doping using a monolayer of a metal terpyridine complex allows to control the interaction between the conduction electrons and localized magnetic moments in the Pt film. The interaction was probed by measuring the weak antilocalization, which demonstrates enhanced magnetic impurity scattering induced by the molecular spin doping. By measuring the spin-orbit torque generated by Pt doped with molecular spins, we found that the spin Hall effect is robust against the magnetic impurity scattering, showing that the significant spin-orbit coupling dominates the charge-to-spin conversion in Pt. These results demonstrate that the molecular spin doping paves the way to explore spin-orbitronics phenomena.

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Quantification of electrogenerated chemiluminescence from tris(bipyridine)ruthenium(ii) and hydroxyl ions

Fiorani A., Valenti G., Irkham , Paolucci F., Einaga Y.

Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics) 22 ( 27 ) 15413 - 15417 2020.07

ISSN 14639076

© 2020 the Owner Societies. In this work, we quantify the electrogenerated chemiluminescence arising from the reaction of electrogenerated tris(bipyridine)ruthenium(iii) with hydroxyl ions, in terms of emission intensity and reaction rate. Different electrode materials (glassy carbon and boron-doped diamond) and different supporting electrolytes (perchlorate, phosphate, and carbonate) were investigated with pH variation. Relative quantification of the electrogenerated chemiluminescence was achieved using the Ru(bpy)32+/tri-n-propylamine system, taken as a reference, with relative emission as low as 600 and 230 times that observed at the same coreactant concentration and the same pH, respectively. The kinetics was investigated by foot of the wave analysis of cyclic voltammetry to measure the turnover frequency of the reaction. This journal is

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Electrochemical reduction of nitrate on boron-doped diamond electrodes: Effects of surface termination and boron-doping level

Kuang P., Natsui K., Feng C., Einaga Y.

Chemosphere (Chemosphere) 251 2020.07

ISSN 00456535

© 2020 Elsevier Ltd This study is among the first to systematically study the electrochemical reduction of nitrate on boron-doped diamond (BDD) films with different surface terminations and boron-doping levels. The highest nitrate reduction efficiency was 48% and the highest selectivity in the production of nitrogen gas was 44.5%, which were achieved using a BDD electrode with a hydrogen-terminated surface and a B/C ratio of 1.0%. C–H bonds served as the anchor points for attracting NO3− anions close to the electrode surface, and thus accelerating the formation of NO3−(ads). Compared to oxygen termination, hydrogen-terminated BDD exhibited higher electrochemical reactivity for reducing nitrate, resulting from the formation of shallow acceptor states and small interfacial band bending. The hydrophobicity of the hydrogen-terminated BDD inhibited water electrolysis and the subsequent adsorption of atomic hydrogen, leading to increased selectivity in the production of nitrogen gas. A BDD electrode with a boron-doping level of 1.0% increased the density of acceptor states, thereby enhancing the conductivity and promoting the formation of C–H bonds after the cathodic reduction pretreatment leading to the direct reduction of nitrate.

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Effect of sp<sup>2</sup> species in a boron-doped diamond electrode on the electrochemical reduction of CO<inf>2</inf>

Xu J., Einaga Y.

Electrochemistry Communications (Electrochemistry Communications) 115 2020.06

ISSN 13882481

© 2020 The Authors The effect of sp2 carbon within a boron-doped diamond (BDD) electrode on the electrochemical reduction of CO2 is investigated for the first time. With increasing sp2 content, the Faradaic efficiency for the production of hydrogen (H2) under constant current density increases while that for the production of formic acid (HCOOH) decreases. Moreover, favorable electrolysis conditions for producing HCOOH shift in the negative potential direction with increasing sp2 content. This phenomenon is ascribed to the presence of adsorption sites on the sp2 carbon. This work provides guidance for selectively controlling the reduction of CO2 by adjusting the distribution of carbonaceous species in the BDD electrode.

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Improving the CO<inf>2</inf> electrochemical reduction to formic acid using iridium-oxide-modified boron-doped diamond electrodes

Jiwanti P.K., Ichzan A.M., Dewandaru R.K.P., Atriardi S.R., Einaga Y., Ivandini T.A.

Diamond and Related Materials (Diamond and Related Materials) 106 2020.06

ISSN 09259635

© 2020 Elsevier B.V. Modification of iridium on the surface of boron-doped diamond (BDD) electrode has been performed to decrease the overpotential reduction of carbon dioxide (CO2) and produce value-added carbon compounds. The modification was performed using the cyclic voltammetry (CV) technique that successfully deposited iridium oxide on the surface of the BDD electrode with an Ir-to-C ratio of approximately 1:100. When the modified BDD electrode was utilized for CV of a dissolved-CO2-saturated solution, hydrogen evolution occurred at a potential of approximately −1.2 V (vs. Ag/AgCl), which was lower than that when an unmodified BDD was used. Furthermore, when this electrode was utilized for amperometry of the same solution at −1.7 V for 1 h, formic acid (HCOOH) was produced with a Faradaic efficiency of approximately 50%. Results indicated that the modified electrode has considerable potential for application to CO2 electrochemical reduction.

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Enhancement of coercivity of self-assembled stacking of ferrimagnetic and antiferromagnetic nanocubes

Sawano K., Tsukiyama K., Shimizu M., Takasaki M., Oaki Y., Yamamoto T., Einaga Y., Jenewein C., Cölfen H., Kaiju H., Sato T., Imai H.

Nanoscale (Nanoscale) 12 ( 14 ) 7792 - 7796 2020.04

ISSN 20403364

© The Royal Society of Chemistry . The coercivity of magnetic nanoparticles is enhanced by the exchange coupling effect at the interface of ferrimagnetic and antiferromagnetic self-assembled monolayers. Antiferromagnetic Co3O4 nanocubes were regularly stacked on an ordered monolayer of ferrimagnetic Fe3O4 nanocubes by layer-by-layer manipulation using evaporation-driven self-assembly. The ordered arrangements of the ferrimagnetic and antiferromagnetic nanocubes are effective for the enhancement of the ferromagnetic character.

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Stable iridium-modified boron-doped diamond electrode for the application in electrochemical detection of arsenic (III)

Agustiany T., Khalil M., Einaga Y., Jiwanti P., Ivandini T.

Materials Chemistry and Physics (Materials Chemistry and Physics) 244 2020.04

ISSN 02540584

© 2020 Elsevier B.V. Preparation of stable iridium-modified boron-doped diamond electrodes through electrodeposition was studied. The electrode was prepared by wet chemical seeding and thermal annealing that performed before and after the electrodeposition process in order to get a homogeneous deposition. The modified electrode from each step was characterized using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Raman and X-Ray photoelectron spectroscopy (XPS) to understand the surface topography and its elemental composition. In addition, cyclic voltammetry for arsenic (III) was performed to examine the electrochemical behavior of the modified diamond. At an optimum condition in a phosphate buffer solution pH 3 and a scan rate of 50 mV/s, a linear calibration curve in the concentration range of 1–100 μM with a detection limit of 4.64 μM was achieved. Excellent stability and repeatability were also observed with relative standard deviations of 2.6% and <0.4%, respectively. Additionally, the electrode exhibited good linearity and sensitivity towards the measurement of arsenic (III) in both arsenic (III)-added tap water and lake water samples.

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Avian Influenza Virus Detection by Optimized Peptide Termination on a Boron-Doped Diamond Electrode

Matsubara T., Ujie M., Yamamoto T., Einaga Y., Daidoji T., Nakaya T., Sato T.

ACS Sensors (ACS Sensors) 5 ( 2 ) 431 - 439 2020.02

Copyright © 2020 American Chemical Society. The development of a simple detection method with high sensitivity is essential for the diagnosis and surveillance of infectious diseases. Previously, we constructed a sensitive biosensor for the detection of pathological human influenza viruses using a boron-doped diamond electrode terminated with a sialyloligosaccharide receptor-mimic peptide that could bind to hemagglutinins involved in viral infection. Circulation of influenza induced by the avian virus in humans has become a major public health concern, and methods for the detection of avian viruses are urgently needed. Here, peptide density and dendrimer generation terminated on the electrode altered the efficiency of viral binding to the electrode surface, thus significantly enhancing charge-transfer resistance measured by electrochemical impedance spectroscopy. The peptide-terminated electrodes exhibited an excellent detection limit of less than one plaque-forming unit of seasonal H1N1 and H3N2 viruses. Furthermore, the improved electrode was detectable for avian viruses isolated from H5N3, H7N1, and H9N2, showing the potential for the detection of all subtypes of influenza A virus, including new subtypes. The peptide-based electrochemical architecture provided a promising approach to biosensors for ultrasensitive detection of pathogenic microorganisms.

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Microfluidic screening system based on boron-doped diamond electrodes and dielectrophoretic sorting for directed evolution of NAD(P)-dependent oxidoreductases

Goto H., Kanai Y., Yotsui A., Shimokihara S., Shitara S., Oyobiki R., Fujiwara K., Watanabe T., Einaga Y., Matsumoto Y., Miki N., Doi N.

Lab on a Chip (Lab on a Chip) 20 ( 4 ) 852 - 861 2020.02

ISSN 14730197

This journal is © The Royal Society of Chemistry. We report the development of a micro total analysis system (μTAS) based on electrochemical measurements and dielectrophoretic sorting for screening of NAD(P)-dependent oxidoreductases. In this system, the activity of enzymes immobilized on microbeads, together with their encoding DNA, can be measured with a boron-doped diamond (BDD) electrode in each compartment (∼30 nL) of the microfluidic system. The 30 nL droplets containing microbead-displayed genes of enzymes with higher activity can then be recovered by dielectrophoretic sorting. Previously, we developed the NAD(P)H-measuring device containing the BDD electrode for high-throughput measurement of the activity of NAD(P)-dependent oxidoreductases. In this study, we fabricated an encapsulating device and a droplet-sorting device for nanoliter-size droplets, for the first time, and then combined these three devices to construct a μTAS for directed evolution of NAD(P)-dependent oxidoreductases. We confirmed that this system works by proof-of-principle experiments and successfully applied this system for screening of randomized libraries of NAD-dependent dehydrogenases.

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Unusual Electrochemical Properties of Low-Doped Boron-Doped Diamond Electrodes Containing sp<sup>2</sup> Carbon

Xu J., Yokota Y., Wong R.A., Kim Y., Einaga Y.

Journal of the American Chemical Society (Journal of the American Chemical Society) 142 ( 5 ) 2310 - 2316 2020.02

ISSN 00027863

Copyright © 2020 American Chemical Society. Unexpected phenomena displayed by low-boron-doped diamond (BDD) electrodes are disclosed in the present work. Generally, the presence of sp2 nondiamond carbon impurities in BDD electrodes causes undesirable electrochemical properties, such as a reduced potential window and increased background current, etc. However, we found that the potential window and redox reaction in normally doped (1%) BDD and low-doped (0.1%) BDD exhibited opposite tendencies depending on the extent of sp2 carbon. Moreover, we found that contrary to the usual expectations, low-doped BDD containing sp2 carbon hinders electron transfer, whereas in line with expectations, normally doped BDD containing sp2 exhibits enhanced electron transfer. Surface analyses by X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS) and electrochemical methods are utilized to explain these unusual phenomena. This work indicates that the electrochemical properties of low-doped BDD containing sp2 might be due partially to the high level of surface oxygen, the large work function, the low carrier density, and the existence of different types of sp2 carbon.

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Electrogenerated Chemiluminescence by in Situ Production of Coreactant Hydrogen Peroxide in Carbonate Aqueous Solution at a Boron-Doped Diamond Electrode

Irkham , Fiorani A., Valenti G., Kamoshida N., Paolucci F., Einaga Y.

Journal of the American Chemical Society (Journal of the American Chemical Society) 142 ( 3 ) 1518 - 1525 2020.01

ISSN 00027863

© 2019 American Chemical Society. An electrogenerated chemiluminescence (ECL) system by in situ coreactant production, where Ru(bpy)32+ emission is generated at a boron-doped diamond (BDD) electrode, is presented. The system takes advantage of the unique properties of BDD to promote oxidation of carbonate (CO32-) into peroxydicarbonate (C2O62-), which further reacts with water to form hydrogen peroxide (H2O2), which acts as a coreactant for Ru(bpy)32+ ECL. Investigation of the mechanism reveals that ECL emission is triggered by the reduction of H2O2 to hydroxyl radicals (OH•), which later react with the reduced Ru(bpy)3+ molecules to form excited states, followed by light emission. The ECL signal was found to increase with the concentration of CO32- therefore, with the concentration of electrogenerated H2O2, although at the same time, higher concentrations of H2O2 can quench the ECL emission, resulting in a decrease in intensity. The carbonate concentration, pH, and oxidation parameters, such as potential and time, were optimized to find the best emission conditions.

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An electrochemical aptamer-based sensor prepared by utilizing the strong interaction between a DNA aptamer and diamond

Asai K., Yamamoto T., Nagashima S., Ogata G., Hibino H., Einaga Y.

Analyst (Analyst) 145 ( 2 ) 544 - 549 2020.01

ISSN 00032654

© 2020 The Royal Society of Chemistry. Stable and continuous biosensing of electroactive species in vivo has been achieved by using boron-doped diamond (BDD) electrodes owing to their outstanding electrochemical properties. However, the present problem in biosensing using BDD electrodes is how to specifically measure/detect the target molecules, including electrochemically inactive species. A possible solution is to fabricate an electrochemical aptamer-based (E-AB) sensor using a BDD electrode. In a preliminary investigation, we found that DNA aptamers strongly adsorb on the BDD surface and the aptamer-adsorbed BDD apparently worked as an E-AB sensor. The present study reports the performance of the aptamer-adsorbed BDD electrode as an E-AB sensor. Doxorubicin (DOX), a widely used chemotherapeutic, was chosen as a target molecule. The sensor could be prepared by just dipping BDD in an aptamer solution for only 30 min, and the electrochemical signals were dependent on the DOX concentration. The adsorption of DNA was strong enough for continuous measurements and even a sonication treatment. Such behaviors were not observed when using gold and glassy carbon electrodes. In a kinetic measurement, distortion by a sluggish response was observed for both association and dissociation phases, indicating that the interaction between DOX and the aptamer involves several kinetic processes. By fitting to a Langmuir isotherm, a limit of detection of 49 nM and a maximum detectable concentration of 2.3 μM were obtained. Although the sensitivity was lower than those of the well-established E-AB sensors of gold, the values are within a drug's therapeutic range. Overall, the present work demonstrates that a DNA aptamer and a BDD electrode is an effective combination for an E-AB sensor with stable sensitivity, and a wide variety of DNA aptamers can be applied without any special treatment.

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Electrochemical Measurement of Bismuth Clusters in Dendrimer Through Transformation from Atomicity Controlled Complexes

Kambe T., Imaoka S., Hasegawa R., Tsukamoto T., Imaoka T., Natsui K., Einaga Y., Yamamoto K.

Journal of Inorganic and Organometallic Polymers and Materials (Journal of Inorganic and Organometallic Polymers and Materials) 30 ( 1 ) 169 - 173 2020.01

ISSN 15741443

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. Dendrimers can provide unique reaction space for sub-nano sized materials. Recently, we have demonstrated a luminous bismuth dendrimer and the on/off switching by stepwisely assembled bismuth units in a phenylazomethine dendrimers. In addition, formation of bismuth clusters was also demonstrated by the reduction of the bismuth salts assembled in the dendrimer. In this study, we have revealed the atomicity dependency about the reduction and oxidation potentials of the assembled bismuth complexes and clusters, respectively. The measurements were conducted by the electrochemical process of the bismuth assembled dendritic poly-phenylazomethines.

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Dielectrophoretic sorting system for screening of NAD(P)-dependent oxidoreductases.

Kanai Y., Shimokihara S., Shitara S., Oyobiki R., Watanabe T., Einaga Y., Wakamatsu K., Matsumoto Y., Fujiwara K., Doi N.

21st International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2017 (21st International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2017) 1383 - 1384 2020

ISSN 9780692941836

© 17CBMS-0001. Here we report the development of a flow injection analysis system based on electrochemical measurements and dielectrophoresis for screening of NAD(P)-dependent oxidoreductases. In this system, the activity of enzyme which is immobilized on microbeads together with its encoding DNA can be measured with a boron-doped diamond (BDD) electrode in each compartment (~30 nL) of the microfluidic system, and the large droplets (~30 nL) containing genes of enzymes with higher activity can be recovered by dielectrophoretic sorting.

Further study of CO<inf>2</inf> electrochemical reduction on palladium modified bdd electrode: Influence of electrolyte

Jiwanti P.K., Einaga Y.

Chemistry - An Asian Journal (Chemistry - An Asian Journal) 15 ( 6 ) 910 - 914 2020

ISSN 18614728

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. The study of CO2 electrochemical reduction to useful compounds using bare or modified BDD electrode attracts numerous attentions. Meanwhile, the efficiency of products obtained from CO2 electrochemical reduction is known to be determined by the electrode material and the electrolyte. Formic acid as main product and CO as a minor product, have also been known on the CO2 reduction using BDD electrode. Recently, we reported the successful improvement of CO production from the reduction of CO2 by decorating the surface of BDD electrode with palladium particles. Following this, herein, we present further inves-tigation on electrolyte dependence, including cation and anion dependence and also concentration effect in order to understand deeply the CO2 reduction on surface of palladium modified BDD electrode. The results suggest the use of NaCl and KCl as a catholyte for optimum performance, in addition to the improvement of CO2 reduction product in higher electrolyte concentration.

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Preparation of boron-doped diamond modified by bimetal nickel and zinc

Putri Y.M.T.A., Jiwanti P.K., Irkham , Gunlazuardi J., Einaga Y., Ivandini T.A.

IOP Conference Series: Materials Science and Engineering (IOP Conference Series: Materials Science and Engineering) 902 ( 1 ) 2020

ISSN 17578981

Nickel has been known as a good catalyst due to its high activity and stability, but the potential formation of NiOOH is quite high. In this work, zinc together with nickel was used to modify the surface of boron-doped diamond (BDD) to lower the formation potential of NiOOH. Electro-deposition (multi pulse amperometry) technique was applied at a potential of -1.6 V for 600 s. The prepared electrode (NiZn-BDD) characterized using SEM-EDX and XPS shows that both nickel and zinc were deposited homogenously on the surface of BDD with the ratio of 1:2 for nickel:zinc.

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