Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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Fabrication of boron doped diamond chip electrodes for single drop analysis

Sugitani Ai, Katayama Michinobu, Watanabe Takeshi, Matsumoto Yoshinori, Einaga Yasuaki

RSC Advances 3 ( 48 ) 25636 - 25639 2013.12

As a prototype for a "highly sensitive electrochemical detection system for single drop analysis using boron-doped diamond (BDD) electrodes", a three-electrode system for the measurement of samples consisting of a single drop was fabricated. An Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) system, employing the Bosch process in order to realize high-aspect-ratio near vertical structures, was used to etch the BDD. A single drop (10 μL) was analyzed using the resulting fabricated 'BDD chip electrode' which exhibited the typical superior electrochemical properties of BDD electrodes. © 2013 The Royal Society of Chemistry.

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Structure-distortion-induced photomagnetic effect in azobenzene/ polyoxometalate Langmuir-Blodgett films

Yamamoto Takashi, Umemura Yasushi, Einaga Yasuaki

Dalton Transactions 42 ( 45 ) 16014 - 16020 2013.12

ISSN 1477-9226

We have prepared photomagnetic Langmuir-Blodgett films composed of an amphiphilic azobenzene and a magnetic polyoxometalate. The obtained film possesses a well-organized layered structure where polyoxometalate anions are sandwiched by azobenzene cations in a single-layered manner. Reversible photoisomerization of azobenzene was achieved even at low temperature, accompanying intensity changes in the d-d transition of polyoxometalate anions. The photomagnetic effect was observed reversibly upon alternate UV and visible light irradiation. Based on polarized spectroscopy, the observed photomagnetic effect is ascribed to the structure-distortion of polyoxometalate layers. © 2013 The Royal Society of Chemistry.

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A neutral Fe(iii) compound exhibiting a two-step spin transition and dielectric anomalies

Li Zhao Yang, Dai Jing Wei, Gagnon Kevin J., Cai Hong Ling, Yamamoto Takashi, Einaga Yasuaki, Zhao Han Hua, Kanegawa Shinji, Sato Osamu, Dunbar Kim R., Xiong Ren Gen

Dalton Transactions 42 ( 41 ) 14685 - 14688 2013.11

ISSN 1477-9226

The mononuclear ferric compound Fe(H-5-Cl-thsa-Me)(5-Cl-thsa-Me) ·H₂O (1) was synthesized and characterized using powder/single-crystal X-ray diffraction, Mössbauer spectroscopy, differential scanning calorimetry (DSC), and magnetic susceptibility measurements. This photo-responsive compound shows reversible, two-step spin-crossover behaviour. Moreover, dielectric anomalies were observed during the spin transitions, demonstrating the multifunctional properties of compound 1. © 2013 The Royal Society of Chemistry.

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Modulation of critical current density in polycrystalline boron-doped diamond by surface modification

Natsui Keisuke, Yamamoto Takashi, Watanabe Takeshi, Kamihara Yoichi, Einaga Yasuaki

Physica Status Solidi (B) Basic Research 250 ( 9 ) 1943 - 1949 2013.09

ISSN 0370-1972

The maximum current flowed with zero resistance, referred to the critical current density, is desired to be sufficiently large in order to apply superconducting wire rods and electromagnets to various devices. Although the critical current density can be enhanced by introduction of non-superconducting impurities, the transition temperature would become diminished in such a case. Here, we report modulation of a critical current density in heavily boron-doped diamonds (BDDs) by changing the surface-termination without introducing any impurity. The surface of a BDD was changed between hydrogen- and oxygen-termination. As a result, the critical current density could be modulated in a reversible manner between the hydrogen- and oxygen-terminated diamonds with maintenance of the superconducting transition temperature. This is because the volume fractions of the superconducting phases were modulated by surface modification. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Application of boron-doped diamond microelectrodes for dental treatment with pinpoint ozone-water production

Ochiai Tsuyoshi, Ishii Yuya, Tago Shoko, Hara Masayuki, Sato Takuya, Hirota Kazuo, Nakata Kazuya, Murakami Taketoshi, Einaga Yasuaki, Fujishima Akira

ChemPhysChem 14 ( 10 ) 2094 - 2096 2013.07

ISSN 1439-4235

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Influence of supporting electrolyte on the electrochemical oxidation of formic acid on boron-doped diamond electrodes

Fierro Stéphane, Honda Yuki, Einaga Yasuaki

Bulletin of the Chemical Society of Japan 86 ( 6 ) 749 - 754 2013.06

ISSN 0009-2673

The influence of support electrolyte on the electrochemical degradation of formic acid was studied on boron-doped diamond (BDD) electrodes. Experimental data are compared with a theoretical model, which is based on organic degradation via hydroxyl radicals under current or mass transport controlled regimes depending on the difference between the applied and limiting current. The kinetics of the different reactions involved in the process is also briefly studied. It is shown that when sulfuric acid is used as support electrolyte, the reactions involving electro-generated peroxodisulfate anions during the degradation of formic acid are highly dependent on temperature. For this reason, the influence on the overall process of the chemical reaction between these anions and formic acid tends to increase with increasing temperatures and when the electrolysis becomes controlled by mass transport. However, it is proven that degradation of formic acid in the bulk occurs under current controlled regime as well. Furthermore, it is shown that the use of sulfuric acid as support electrolyte enhances the degradation of formic acid at high temperatures and when the process is controlled by mass transfer compared to other inert support electrolytes. © 2013 The Chemical Society of Japan.

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Development of electrolyte-free ozone sensors using boron-doped diamond electrodes

Ishii Yuya, Ivandini Tribidasari A., Murata Kazutaka, Einaga Yasuaki

Analytical Chemistry 85 ( 9 ) 4284 - 4288 2013.05

ISSN 0003-2700

The electrochemical detection of dissolved ozone in water was examined using boron-doped diamond (BDD) electrodes. A well-defined reduction peak was observed at ∼380 mV for H-terminated BDD, whereas it was observed at ∼200 mV in the case of O-terminated BDD for an ozone solution in a 0.1 M phosphate buffer solution at pH 7. The peak potential for ozone reduction was selective with respect to oxygen reduction at both H- and O-terminated BDD electrodes, whereas it occurred at approximately the same potential as oxygen reduction at other types of solid electrodes, including glassy-carbon, platinum, and gold electrodes. Interference from chlorine was not observed in lower concentration than 300 μM ClO^-. Furthermore, in order to apply the detection technique to electrolyte-free media, BDD microelectrodes were also used. A linear calibration curve for dissolved ozone in water could be achieved between concentrations of 0.49 and 740 μM, with an estimated detection limit (S/N = 3) of 0.185 μM (S/N = 3). Excellent stability was demonstrated for repetitions of these calibration curves performed in 3 consecutive days. © 2013 American Chemical Society.

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Electrochemical detection of lipophilic antioxidants with high sensitivity at boron-doped diamond electrode

Kondo Takeshi, Sakai Kazuya, Watanabe Takeshi, Einaga Yasuaki, Yuasa Makoto

Electrochimica Acta 95 205 - 211 2013.04

ISSN 0013-4686

The electrochemical detection of lipophilic antioxidants, α-tocopherol (vitamin E, VE) and ubiquinone (coenzyme Q₁₀, CoQ₁₀), in methanol and in methanol/hexane mixture solutions, respectively, at boron-doped diamond (BDD) electrodes was investigated by cyclic voltammetry (CV) and flow-injection electrochemical measurements. CV measurements revealed that the overpotential for electrochemical reaction of VE and CoQ₁₀ was larger at an oxidized BDD electrode surface than at that of a hydrogenated BDD (H-BDD) electrode. The slope of the CV calibration curve used to determine the VE and CoQ₁₀ concentrations was larger at a glassy carbon (GC) electrode than at the H-BDD electrode; however, the signal-to-background ratio was larger at the H-BDD electrode than at the GC electrode, due to the low background feature of the H-BDD electrode. The limit of detection (LOD), defined by a signal-to-noise ratio of three for flow-injection electrochemical detection, was much smaller at the H-BDD electrode (VE: 41 nM and CoQ₁₀: 17 nM) than at the GC electrode (VE: 263 nM and CoQ₁₀: 71 nM). These results confirm that the H-BDD electrode is reliable for the electrochemical detection of lipophilic antioxidants, especially at low concentrations. © 2013 Elsevier Ltd. All rights reserved.

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Simultaneous detection of iodine and iodide on boron doped diamond electrodes

Fierro Stéphane, Comninellis Christos, Einaga Yasuaki

Talanta 103 33 - 37 2013.01

ISSN 0039-9140

Individual and simultaneous electrochemical detection of iodide and iodine has been performed via cyclic voltammetry on boron doped diamond (BDD) electrodes in a 1 M NaClO₄ (pH 8) solution, representative of typical environmental water conditions. It is feasible to compute accurate calibration curve for both compounds using cyclic voltammetry measurements by determining the peak current intensities as a function of the concentration. A lower detection limit of about 20 μM was obtained for iodide and 10 μM for iodine. Based on the comparison between the peak current intensities reported during the oxidation of KI, it is probable that iodide (I^-) is ?rst oxidized in a single step to yield iodine (I₂). The latter is further oxidized to obtain IO₃
^-. This technique, however, did not allow for a reasonably accurate detection of iodate (IO₃ ^-) on a BDD electrode. © 2012 Elsevier B.V. All rights reserved.

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Controlling the diffusion profile of electroactive species for selective anodic stripping voltammetry of cadmium at boron-doped diamond electrodes

Sugitani Ai, Watanabe Takeshi, Ivandini Tribidasari A., Iguchi Tatsuo, Einaga Yasuaki

Physical Chemistry Chemical Physics 15 ( 1 ) 142 - 147 2013.01

ISSN 1463-9076

Selective anodic stripping voltammetry of trace metal ions in a mixture solution with another interfering metal was developed based on Fick's law concerning the diffusion profile of interfering metals at the electrode surface after electrolysis treatment. A boron-doped diamond film was used as the sensing electrode, while a perforated carbon sheet was used for the interference-depleting electrode. The influence of the electrode distance and the time of electrolysis on the formation of the diffusion profile was studied. As a working model, the detection of cadmium with copper interference was investigated. The advantage of the method in comparison to general electrolysis was also discussed. The method offers a new perspective for improving the selective detection of metal ions by analyzing the diffusion profiles of the interfering species at the surface of electrodes. © the Owner Societies 2013.

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Electrochemical Detection of Selenium (IV) and (VI) at Gold-Modified Diamond Electrodes

Ivandini Tribidasari A., Einaga Yasuaki

Electrocatalysis 4 ( 4 ) 367 - 374 2013

ISSN 1868-2529

Electrochemical detection of Se (IV) and (VI) was investigated at gold-modified boron-doped diamond electrodes. Cyclic voltammetry in acid condition showed that the onset of current flows of Se (IV) and Se (VI) occurred at almost similar potentials. Furthermore, the currents at the peak potential of ∼0.9 V (vs. Ag/AgCl) showed high linearity against concentrations of both Se (IV) and Se (VI) with estimated limits of detection (S/N = 3) of 20 and 50 ppb, respectively. However, whereas oxidation peaks of Se (IV) and Se (VI) can be observed in acid and neutral pH, only oxidation peak of Se (IV) appeared in high pH. The possibility to differentiate a mixture of Se (IV) and Se (VI) by applying cyclic voltammogram (CV) at acidic and basic conditions was discussed, and it was promising, especially because, previously, it always stated that Se (VI) was not electrochemically active. © 2013 Springer Science+Business Media New York.

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In vivo pH monitoring using boron doped diamond microelectrode and silver needles

Fierro Stéphane, Seishima Ryo, Nagano Osamu, Saya Hideyuki, Einaga Yasuaki

Scientific Reports 3 2013

This study presents the in vivo electrochemical monitoring of pH using boron doped diamond (BDD) microelectrode and silver needles for potential application in medical diagnosis. Accurate calibration curve for pH determination were obtained through in vitro electrochemical measurements. The increase induced in stomach pH by treatment with pantoprazole was used to demonstrate that it is possible to monitor the pH in vivo using the simple and noninvasive system proposed herein. Using the results of the in vivo and in vitro experiments, a quantitative analysis of the increase in stomach pH is also presented. It is proposed that the catheter-free pH monitoring system presented in this study could be potentially employed in any biological environment.

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Development of a biochemical oxygen demand sensor using gold-modified boron doped diamond electrodes

Ivandini Tribidasari A., Saepudin Endang, Wardah Habibah, Harmesa [No Value], Dewangga Netra, Einaga Yasuaki

Analytical Chemistry 84 ( 22 ) 9825 - 9832 2012.11

ISSN 0003-2700

Gold-modified boron doped diamond (BDD) electrodes were examined for the amperometric detection of oxygen as well as a detector for measuring biochemical oxygen demand (BOD) using Rhodotorula mucilaginosa UICC Y-181. An optimum potential of -0.5 V (vs Ag/AgCl) was applied, and the optimum waiting time was observed to be 20 min. A linear calibration curve for oxygen reduction was achieved with a sensitivity of 1.4 μA mg^-1 L oxygen. Furthermore, a linear calibration curve in the glucose concentration range of 0.1-0.5 mM (equivalent to 10-50 mg L^-1 BOD) was obtained with an estimated detection limit of 4 mg L^-1 BOD. Excellent reproducibility of the BOD sensor was shown with an RSD of 0.9%. Moreover, the BOD sensor showed good tolerance against the presence of copper ions up to a maximum concentration of 0.80 μM (equivalent to 50 ppb). The sensor was applied to BOD measurements of the water from a lake at the University of Indonesia in Jakarta, Indonesia, with results comparable to those made using a standard method for BOD measurement. © 2012 American Chemical Society.

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Highly sensitive detection of Cr ⁶⁺ on boron doped diamond electrodes

Fierro Stéphane, Watanabe Takeshi, Akai Kazumi, Einaga Yasuaki

Electrochimica Acta 82 9 - 11 2012.11

ISSN 0013-4686

Electrochemical detection of Cr ⁶⁺ has been performed by cyclic and linear scan voltammetry on boron doped diamond (BDD) electrode. This method is based on the electrochemical reduction of Cr ⁶⁺ to Cr ³⁺. The resulting voltammograms exhibited a clear peak at 0.03 V vs. AgCl related to this reduction and highly accurate (r ² = 0.99) calibration curves could be obtained for a chromium concentration range between 10 ppb and 5 ppm. The influence of other metals dissolved in solution (Cu, Cd, Pb, B and Se) has been investigated as well and it was found that the Cr ⁶⁺ calibration curves remained unaltered. For all the experiments performed, a detection limit around 3 ppb was achieved. The high accuracy and reproducibility of the results as well as the excellent stability of the electrode material proves the excellent capabilities of this system for chromium detection. © 2012 Elsevier Ltd.

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Paramagnetic phase of a heavy-fermion compound, CeFePO, probed by< ⁵⁷Fe mössbauer spectroscopy

Nakamura Tetsur, Yamamoto Takash, Matoba Masanor, Einaga Yasuak, Kamihara Yoich

Journal of the Physical Society of Japan 81 ( 6 ) 2012.06

ISSN 0031-9015

⁵⁷Fe Mössbauer spectroscopy was applied to an iron-based layered compound CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed in the Mössbauer spectra of CeFePO indicating a paramagnetic phase of the Fe magnetic sublattice. All the spectra were fitted with a small quadrupole splitting, and the Debye temperature of CeFePO was found to be ∼448 K. The isomer shift at room temperature, 0.32 mm/s, was almost equal to those of LnFeAsO (Ln = La, Ce, Sm). Comparing s-electron density using the isomer shifts and unit cell volumes, it was found that the Fe of CeFePO has a similar valence state to other layered iron-based quaternary oxypnictides except LaFePO. © 2012 The Physical Society of Japan.

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Anodic oxidation on a boron-doped diamond electrode mediated by methoxy radicals

Sumi Takenori, Saitoh Tsuyoshi, Natsui Keisuke, Yamamoto Takashi, Atobe Mahito, Einaga Yasuaki, Nishiyama Shigeru

Angewandte Chemie - International Edition 51 ( 22 ) 5443 - 5446 2012.05

ISSN 1433-7851

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Cooperative spin transition and thermally quenched high-spin state in new polymorph of [Fe(qsal) ₂]I ₃

Takahashi Kazuyuki, Sato Tetsuya, Mori Hatsumi, Tajima Hiroyuki, Einaga Yasuaki, Sato Osamu

Hyperfine Interactions 206 ( 1-3 ) 1 - 5 2012.03

ISSN 0304-3843

Novel polymorph of the ferric spin crossover complex, β-[Fe(qsal) ₂]I ₃ [qsalH = N-(8-quinolyl)salicylaldimine], has been prepared and characterized by magnetic susceptibilities and Mössbauer spectra. β polymorph exhibited a cooperative complete spin transition with a thermal hysteresis of 25 K and a tendency to be quenched in the high-spin (HS) state, which is contrastive to a gradual incomplete spin conversion in α polymorph. © 2011 Springer Science+Business Media B.V.

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Anodic Oxidation on a Boron-Doped Diamond Electrode Mediated by Methoxy Radicals.

EINAGA YASUAKI

Angew. Chem. Int. Ed. 2012

Research paper (scientific journal), Single Work

Dopamine detection on boron-doped diamond electrodes using fast cyclic voltammetry

Kato Taisuke, Fierro Stéphane, Watanabe Takeshi, Yoshimi Kenji, Einaga Yasuaki

Chemistry Letters 41 ( 3 ) 224 - 226 2012

ISSN 0366-7022

A new method is proposed for the accurate and reproducible detection of dopamine using cyclic voltammetry on boron-doped diamond (BDD) electrode. It is shown that reproducible voltammograms can be obtained when applying a relatively high scan rate (100Vs ^-1) during the detection measurements. For lower scan rates (1Vs ^-1), it is proven that electrode fouling occurs due do the deposition of a polymer at the electrode surface arising from the oxidation of aminochrome. Cyclic voltammetry measurements of the [Fe(CN) ₆] ^3-/[Fe(CN) ₆] ^4- couple performed before and after dopamine detection on BDD and glassy carbon electrodes have shown that the electrochemical activity of the electrode decreases only at low scan rates for BDD dopamine (DA) detection, which leads to electrode poisoning whereas the activity remains unchanged for higher scan rates. However, on glassy carbon electrodes, the electrochemical activity of the material decreases after DA detection measurements independently of the scan rate applied. Therefore, this study shows that electrode fouling during the detection of dopamine by cyclic voltammetry can be avoided only when using BDD electrode but also only for high applied scan rates. © 2012 The Chemical Society of Japan.

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In vivo assessment of cancerous tumors using boron doped diamond microelectrode

Fierro Stéphane, Yoshikawa Momoko, Nagano Osamu, Yoshimi Kenji, Saya Hideyuki, Einaga Yasuaki

Scientific Reports 2 2012

The in vitro and in vivo electrochemical detection of the reduced form of glutathione (L-γ-glutamyl-L-cysteinyl-glycine, GSH) using boron doped diamond (BDD) microelectrode for potential application in the assessment of cancerous tumors is presented. Accurate calibration curve for the determination of GSH could be obtained by the in vitro electrochemical measurements. Additionally, it was shown that it was possible to separate the detection of GSH from the oxidized form of glutathione (GSSG) using chronoamperometry measurements. In vivo GSH detection measurements have been performed in human cancer cells inoculated in immunodeficient mice. These measurements have shown that the difference of GSH level between cancerous and normal tissues can be detected. Moreover, GSH detection measurements carried out before and after X-ray irradiation have proved that it is possible to assess in vivo the decrease in GSH concentration in the tumor after a specific treatment.

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