Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
Volume 71 , Issue 6
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  • Takeo HYODO, Yasuhiro SHIMIZU, Makoto EGASHIRA
    2003 Volume 71 Issue 6 Pages 387-393
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    Preparation, characterization and gas-sensing properties of mesoporous SnO2 powders have been described. SnO2 powders prepared from sodium stannate by utilizing a self-assembly of n-cetylpyridinium chloride were characterized to have hexagonally ordered mesoporous structure (d100≈4.4 nm). Treatment of the as-prepared powders with phosphoric acid was effective for depressing the growth of SnO2 crystallites and then maintaining the ordered mesoporous structure (d100≈3.1 nm, mean pore diameter≈1.5-2.5 nm) up to elevated temperatures, while the pore volume decreased. H2 sensitivity of mesoporous SnO2 was largely dependent on its specific surface area, the sensitivity being highest (Rg/Ra≈337 to 1000 ppm H2 at 400°C) with the highest specific surface area (374 m2 g-1 after calcination at 600°C). Mesoporous SnO2 powder with larger mesopores (mean pore diameter: ca. 5.2 nm, surface area: 198 m2 g-1 after calcination at 600°C), which was prepared by utilizing a block copolymer with a large molecular weight (ca. 5800) as a surfactant, showed higher H2 sensitivity (Rg/Ra≈77 to 1000 ppm H2 at 400°C) than that of n-cetylpyridinium chloride-derived SnO2 with the same surface area but smaller mesopores. However, electrical resistance levels in air of the monolith sensors based on the mesoporous materials were close to the limit for practical measurement. Then, the mesoporous SnO2 was utilized as a surface coating layer of conventional SnO2 powder, which was prepared by pyrolysis of tin oxalate. The coating was effective for improving the gas-sensing properties, while maintaining the sensor resistance in air at a practical level. For example, NOx sensitivity of conventional SnO2 markedly increased with the coating, while H2 sensitivity of the coated sensor was lower than that of mesoporous SnO2.

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Communications
  • Shinji NAKAGOMI, Hideyuki WATANABE, Yoshihiro KOKUBUN
    2003 Volume 71 Issue 6 Pages 394-397
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A fabricated hydrogen sensor diode of Pt - thin TiOx layer - SiC structure was found to exhibit a large voltage response up to 3 volts. Diodes with and without the TiOx layer were compared in terms of current-voltage characteristics. The difference in voltage obtained in an H2 atmosphere and that obtained in an O2 atmosphere at a constant forward current was studied. A simple model consisting of a resistance and Schottky diode connected in series was assumed. The voltage change results from changes in both barrier height and series resistance. The change in series resistance is due to a property of TiOx under exposure to hydrogen.

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  • Atsuko HASHIMOTO, Takashi HIBINO, Kazuyo KOBAYASHI, Mitsuru SANO
    2003 Volume 71 Issue 6 Pages 398-401
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    Resistor-type sensor devices using a samaria-doped ceria electrolyte with different working electrodes were fabricated for detecting carbon monoxide (CO) in reformed gases between 250 and 425°C. The electrochemical oxidation of H2 over a Pd working electrode was the most sensitive to a reversible poisoning by 50-4000 ppm CO in the presence of 50% hydrogen, 10% carbon dioxide, and 6% water vapor, which provided an increase in the electrode-reaction resistance at the electrode-electrolyte interface. The resulting sensor signal was strongly dependent on the CO concentration, where linear relationships between the signal and the logarithm of the CO concentration were obtained, especially below 1000 ppm with 90% response and 90% recovery times of about 20 seconds. An improvement in the CO-sensing properties of the present sensor device above 300°C was also carried out by the addition of Au to the Pd working electrode.

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  • Yasunori HASEGAWA, Atsushi ODA, Nobuhito IMANAKA, Gin-ya ADACHI
    2003 Volume 71 Issue 6 Pages 402-404
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A simple gas sensor system applicable for monitoring various environmentally deteriorating gases was fabricated by the combination of a newly developed cerium ion conducting solid electrolyte, (CexZr1-x)4/(4-x)Nb(PO4)3, and yttria stabilized zirconia (YSZ). By applying the oxycarbonate or the potassium nitrite mixed gadolinium oxide based solid solution as an auxiliary electrode, the sensor can detect CO2 gas or NO gas, respectively, with demonstrating a rapid, continuous, and reproducible response, which obeys the theoretical Nernst relationship. The present sensor fabrication proposes the approaches to pursue for detecting various gases only by exchanging the auxiliary electrode suitable for the target gas sensing.

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  • Takashi ONO, Masaharu HASEI, Akira KUNIMOTO, Norio MIURA
    2003 Volume 71 Issue 6 Pages 405-407
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    The mixed-potential type NOx sensor attached with the oxidation-catalyst electrode was fabricated by laminating and sintering YSZ green-sheets, on which an NOx sensing electrode consisting of metal oxide (Cr2O3), an O2 sensing electrode, an NOx conversion electrode, Pt heaters, and a pair of thermocouples were printed. The sensor was capable of detecting low concentrations of total NOx. The use of the oxidation-catalyst electrode was found to decrease largely the interference of reducing gases (C3H8, CO) to the NOx sensitivity. The results obtained here indicate that the present sensor has great possibility of being utilized as an on-board NOx sensor.

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  • Soichi YABUKI, Fumio MIZUTANI, Yoshiki HIRATA
    2003 Volume 71 Issue 6 Pages 408-410
    Published: June 05, 2003
    Released: August 30, 2019
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    An electrode coated with a bilayer consisting of a polyion complex membrane (PIC) layer on a hemin/ferrocene layer was prepared and applied to measuring H2O2. Response to H2O2 on the electrode was measured at −0.2 V vs. Ag/AgCl; lower detection limit was 1 μM, linear range, up to 50 μM. Current by interferants was completely prevented. In contrast, an electrode with a monolayer consisting of PIC containing hemin and ferrocene showed a discernible interfering current (current ratio by l-ascorbate to H2O2 was ~35%). Thus the bilayer modified electrode has been proved to be useful as a H2O2-sensor even if the electrochemical interferants co-exist in the samples.

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  • Hiroaki MATSUURA, Yukari SATO, Takahiro SAWAGUCHI, Fumio MIZUTANI
    2003 Volume 71 Issue 6 Pages 411-413
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    Organophosphorus pesticides (OPPs), diazinon (0.01-0.05 ppm) and ethylthiometon (0.01-0.2 ppm), were determined by monitoring the activity change of acetylcholinesterase (AChE), based on the chemisorption/desorption-process of thiocholine on a silver electrode as follows. Thiocholine, which was produced through the AChE-catalyzed reaction, was chemisorbed on the silver electrode surface, and then was cathodically desorbed. The electrical charge passed through the desorption process was proportional to the number of adsorbed thiocholine molecules, hence to the AChE activity. Thus the inhibition of the AChE activity by OPPs could be monitored from the decrease in the electrical charge for the desorption process.

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  • Fumio MIZUTANI, Yoshiki HIRATA, Soichi YABUKI, Seiichiro IIJIMA
    2003 Volume 71 Issue 6 Pages 414-416
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    An amperometric ADP-sensing electrode was prepared by immobilizing pyruvate kinase and pyruvate oxidase on an electrode coated with an oxygen-permeable, poly (dimethylsiloxane) layer. The concentration of ADP (2 μM-0.4 mM) could be determined from the decrease in the cathodic current at −0.4 V vs. Ag/AgCl. The bienzyme electrode was applied to the determination of cratine kinase (CK); the enzyme activity (4-1,000 U l-1) was measured from the rate of current decrease, which was caused by the production of ADP through CK-catalyzed reaction.

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  • Masanobu MATSUGUCHI, Masanori TANAKA
    2003 Volume 71 Issue 6 Pages 417-419
    Published: June 05, 2003
    Released: August 30, 2019
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    Piezoelectric devices coated with amino-functional poly(styrene-co-chloromethyl styrene) derivatives were fabricated to develop a simple system that monitors NO2 gas in air. The introduction of NO2 gas irreversibly decreased the oscillation frequencies of all of the devices tested. The sensitivity estimated from the hourly change in the frequency demonstrated a ppm level of NO2 detection. It was also confirmed that other gases, such as O2, CO2, and SO2, functioning as an interference gas, showed little response and good selectivity toward NO2. The effect of humidity was also not serious.

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  • Tatsumi ISHIHARA, Koji KABEMURA, Madoka FUKUYAMA, Atanu DUTTA, Hiroyas ...
    2003 Volume 71 Issue 6 Pages 420-422
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    Amperometric hydrocarbon sensor based on the oxygen pumping current was studied for monitoring hydrocarbon in exhaust gas. It was found that the oxygen pumping current through the sensor using La0.9Sr0.1Ga0.8Mg0.2O3 electrolyte at 1 V application monotonically increased with C3H6 concentration, but hardly depends on oxygen concentration when Pt and SnO2 were used for the active and the inactive electrode for oxidation, respectively. The oxygen pumping current of the developed sensor under 1 V application is hardly changed by coexisting CO and H2O. Consequently, the developed amperometric hydrocarbon sensor can detect hydrocarbon with high selectivity.

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  • Masashi SHOYAMA, Noritsugu HASHIMOTO
    2003 Volume 71 Issue 6 Pages 423-426
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A hetero-layered ZnO/SnO2 thin film was prepared by the sol-gel method to improve the sensing properties for the CO gas. The CO sensitivity and selectivity of the hetero-layered ZnO/SnO2 thin film were both drastically improved than that of the single-layered Pd-SnO2 thin film at a high operating temperature range from 300°C to 500°C. It was considered that the columnar ZnO layer deposited onto the SnO2 layer was very effective in decreasing the influence of the interference gases, such as NOx.

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  • Tsuyoshi ARAKAWA, Masami AKAMINE, Akiko MURAKI
    2003 Volume 71 Issue 6 Pages 427-429
    Published: June 05, 2003
    Released: August 30, 2019
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    The determination of heavy metal ions based on quenching of the rare earth luminescence was investigated. A few heavy metal ions efficiently quenched the luminescence of Ce3+ in polymerized cellulose films which were obtained by Na-CMC (sodium carboxymethyl cellulose) solution and CeCl3 solution or the mixed solution of CeCl3 and a heavy metal chloride. Also, the decay time of Ce3+ ions(τ) in Ce3+-Cu +, Ce3+-Cu2+, Ce3+-Zn2+ and Ce3+-Pb2+ system was shorter than that of only Ce3+ system (τ0). The linear relationship between the concentration of Cu2+, Zn2+ or Pb2+ ions and τ0 reflected the dynamic quenching, as predicted by the Stern-Volmer equation.

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  • K. Vengatajalabathy GOBI, Sook Jin KIM, Ryohei HARADA, Norio MIURA
    2003 Volume 71 Issue 6 Pages 430-432
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A sensor-chip-module integrated portable surface-plasmon-resonance (SPR) immunosensor was employed for monitoring the indirect competitive immunoreaction of the monoclonal antibody against 2-hydroxybiphenyl between the analyte (2-hydroxybiphenyl, abbreviated as HBP hereafter) in test solution and the HBP-protein conjugate immobilized on sensor chip. This sensor was found to detect HBP rather sensitively in the concentration range of 0.1-1000 ppb. The sensor chip could be reusable several times by removing the antibody anchored to the sensor chip on treatment with a pepsin solution (pH 2.0) for a few minutes.

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  • Hiromitsu HACHIYA, Manabu NEGISHI, Megumi ICHIOKA, Seishiro OHYA, Ming ...
    2003 Volume 71 Issue 6 Pages 433-435
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A novel microfabricated electrochemical hydrogen cyanide gas sensor was developed. This sensor consisted of a gas permeable membrane, an electrolyte solution, a working electrode, a counter electrode, a sensor body and other components. Several microparts were produced using microfabrication techniques; a microporous silicon membrane by DeepRIE, a quartz glass sensor body by dicing, and Ag/Pt/Ti thin membranes as electrodes by ECR sputtering. The size of the sensor was 5×5×3 mm, which was 1/467 when the volume compared with commercially available sensors. This sensor showed good performance for hydrogen cyanide gas detection with respect to linearity and rapid-ness of response.

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  • Takatoshi KAYA, Kuniaki NAGAMINE, Daisuke OYAMATSU, Matsuhiko NISHIZAW ...
    2003 Volume 71 Issue 6 Pages 436-438
    Published: June 05, 2003
    Released: August 30, 2019
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    A microbial chip for bioassay was fabricated and its performance was characterized by scanning electrochemical microscopy (SECM). The microbial chip was fabricated by filling the micropores on a glass substrate with collagen gel embedding Escherichia coli (E.coli) cells. For measuring the activity of E.coli cells, the SECM measurement using ferricyanide as an electron mediator showed that the respiration activity of the immobilized E.coli cells increased with the concentration of glucose in the solution. The results suggested that the microbial chip can be used as a chemical sensor for nutritive species.

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  • Daisuke OYAMATSU, Norihiro KANAYA, Yu HIRANO, Matsuhiko NISHIZAWA, Tom ...
    2003 Volume 71 Issue 6 Pages 439-441
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    The immobilization of two enzymes on a pair of Au microband electrodes was performed by using electrochemical desorption of self-assembled monolayer (SAM) of alkanethiol. Both of the Au electrodes were coated with the SAM of n-octadecanethiol (ODT-SAM) at first. The ODT-SAM on one of the Au electrodes was electrochemically removed by applying reductive potential. The resulting naked Au surface was re-coated with the SAM of 2-aminoethanethiol (AET). These treatments resulted in a couple of Au electrodes coated with the ODT-SAM and AET-SAM, respectively. Horseradish peroxidase (HRP) was selectively immobilized on the AET-SAM by using crosslinking agent, glutaraldehyde. On the other hand, diaphorase (Dp) was immobilized on the surface of ODT-SAM by hydrophobic interaction. The imaging of the resulting substrate with scanning electrochemical microscope (SECM) demonstrated the enzymatic activities of HRP and Dp at the AET- and ODT- treated Au electrodes, respectively.

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  • Akane SAKAGUCHI, Wakako TSUGAWA, Stefano FERRI, Koji SODE
    2003 Volume 71 Issue 6 Pages 442-445
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    We recently isolated a novel fructosyl-amine oxidase (FAOD) from the soil bacterium Arthrobacter sp. FV 1-1, cloned the gene encoding FAOD and succeeded in the recombinant production. This bacterial FAOD showed high specificity towards fructosyl valine (FV), a proteolytic product of hemoglobin A1c (HbA1c), but was almost completely inactive towards ε-fructosyl-lysine (ε-FK), a proteolytic product of glycated albumin. By utilizing recombinant FAOD expressed in E. coli, an FAOD sensor based on hydrogen peroxide detection was constructed. The sensor showed FV specificity, with a minimum detectable concentration of 1 μM. The sensitivity was 7.1 mAM-1cm-2, which is 17 times higher than that of the previously reported FAOD-based enzyme sensors. Because the bacterial FAOD-based sensor could detect FV concentration and discriminate FV in the presence of ε-FK, it has the great potential for use in the measurement of HbA1c in whole blood samples.

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  • Mikako SAITO, Shigetoshi HORIKIRI, Hideaki MATSUOKA
    2003 Volume 71 Issue 6 Pages 446-448
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A carbon fiber microelectrode (CFM) was devised and applied to the dielectrophoretic selection of a viable single-cell of rice and BY-2. When 10 MHz electric field was applied, only a viable single-cell could be pulled and picked up within a few sec. This cell selection system was thought to be useful for the high throughput experiment using single-cells.

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  • Yasuhiro IIDA, Yumiko SATO, Ikuo SATOH
    2003 Volume 71 Issue 6 Pages 449-452
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A flow-injection amperometric system for evaluation of the activity of an immobilized α-amylase column was constructed and the system was applied to detect of calcium (II) ions based on the apoenzyme reactivation method. The α-amylase activity was amperometrically evaluated by using a double-layered column which consisted of α-glucosidase and pyranose oxidase. The detection of calcium (II) ions, being the cofactor of α-amylase, was realized by measuring the reactivation of apo-type α-amylase column, which was the recognition element of Ca(II) ions. Maleate buffer (0.1 M, pH 6.0) as a carrier solution was continuously pumped through the system, and sample solutions were introduced into the system via rotary injection valves. The catalytic activity of the multi-enzyme column was assessed by injecting 0.5% starch solution as a substrate. Calcium(II) ions in 1.0 mM levels were detected by using the system based on the apoenzyme reactivation method.

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  • Yasuhiro IIDA, Chiaki GONOKAMI, Taichi MORII, Ikuo SATOH
    2003 Volume 71 Issue 6 Pages 453-455
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A calorimetric flow-injection analysis (FIA) with an immobilized thermolysin column was applied to determination of zinc (II) ions based on the apoenzyme reactivation method. The immobilization yield and the enzyme stability were significantly improved by using NaBr solution for dissolving thermolysin. The catalytic activity of the enzyme-packed column was assessed by injecting 1.0 ml of synthetic oligopeptide solution as a substrate into the system. The column was regenerated on exposure to 100 mM EDTA solution and reversibly reactivated with addition of zinc (II) ions. The reactivation ratio depended on the concentration of zinc (II) ions solution injected. Thus, reactivation ratio was evaluated by injection of various concentrations of zinc(II) ions, and thereby, zinc(II) ions were determined. The zinc(II) ions in a range of 10 to 100 μM were measured.

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Articles
  • Takahiko SASAHARA, Masateru NISHIMURA, Hiroki ISHIHARA, Kazuhiro TOYOD ...
    2003 Volume 71 Issue 6 Pages 457-462
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A catalytic combustion type gas sensor with low heat capacity employing Pd/γ-Al2O3 was fabricated on a silicon substrate by micromachining and screen-printing. The sensor showed a large response peak before reaching a steady-state value upon pulse-heating for 0.2 s or 0.4 s with a cycle of 1-30 s when volatile organic compounds such as alcohol and acid were contained in the environment, while hydrogen and methane did not show such a response peak but a simple increase to a steady-state value. The peak height or area increased with increasing the non-heating period (0.6-29.6 s) and also with the concentration of target gases. The unique peak response has likely arisen from the combustion of the volatile organic molecules adsorbed on the catalytic sensor material during the non-heating period. The response mechanism was supported by temperature programmed desorption experiments of ethanol.

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  • Takashi OYABU, Takeshi ONODERA, Ayako SAWADA, Kozaburo TAKENAKA
    2003 Volume 71 Issue 6 Pages 463-467
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    The purification capabilities of four kinds of foliage plants for formaldehyde, which is a main indoor air pollutant, are examined. The purification capability (Pα) is introduced using a tin oxide gas sensor-output. Pα is derived by dividing the peak value of the sensor-output by the full-width at half maximum. Formaldehyde is one of the typical chemical substances which cause sick-building syndrome. The abilities of the following plants are examined: rubber plant, Boston fern, golden pothos and snake plant. The purification capabilities of these plants for formaldehyde in the amount of 10 ppm are about 19, 15, 23 and 12 respectively. The number becomes greater as the capability is higher. There are several features in Pα characteristics as a function of formaldehyde concentration. Namely, the Pα characteristics for rubber plant and Boston fern can be shown by a linear increasing function. The characteristics are measured until the concentration of 40 ppm. The characteristic of golden pothos is almost constant and the characteristic of snake plant has a maximum value at the concentration of 20 ppm.

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  • Jun TAMAKI, Tomonori HAYASHI, Yoshifumi YAMAMOTO, Masao MATSUOKA
    2003 Volume 71 Issue 6 Pages 468-474
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    SnO2 based gas sensors have been investigated for the detection of aliphatic carboxylic acids (C2~C8). Among SnO2 sensors modified with foreign metal oxide, MoO3-, and WO3-SnO2 sensors showed high sensitivities to aliphatic carboxylic acids, although both sensors exhibited different properties from each other. Catalytic properties of SnO2 based sensor materials have been also evaluated in the oxidation of carboxylic acid in order to be associated with sensing properties. Compared with pure SnO2, the catalytic activity was decreased and the partial oxidation was favored for WO3-SnO2. For MoO3-SnO2, the partial oxidation was promoted with the similar activity to pure SnO2, and the cyclic compound like maleic anhydride was produced in the oxidation of carboxylic acid with carbon number larger than 5. These results mean that the consumption of adsorbed oxygen on the surface of sensor material is decreased due to the addition of WO3 and MoO3. It was found that the catalytic activity was too high and most of carboxylic acid were oxidized at sensor surface for pure SnO2 sensor. On the other hand, for WO3- and MoO3-SnO2 sensors, the catalytic activity was decreased and the partial oxidation was preferred. This causes the consumption of adsorbed oxygen inside the sensor, inducing the enhancement of sensitivity.

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  • Chunying YU, Takeo HYODO, Yasuhiro SHIMIZU, Makoto EGASHIRA
    2003 Volume 71 Issue 6 Pages 475-480
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    TiO2 powder was prepared by employing a modified sol-gel method with Ti(NO3)4 and polyethylene glycol having an average molecular weight of 6000. The as-prepared powder was in anatase phase with a crystallite size of 4.4 nm, and showed a high specific surface area of 214 m2 g-1 involving a small fraction of ordered mesopores with a d-spacing of ca. 4.1 nm. Calcination of the powder at 500°C for 1 h led to fracture of the ordered mesoporous strucutre along with a partial phase transition to rutile and a decrease in specific surface area to 25.5 m2 g-1 so that the ordered mesoporous structure was not thermally stable enough. Phosphoric acid (PA) treatment was found to be effective for improving the thermal stability of the ordered mesoporous structure. In addition, no phase transition and little change in crystallite size were observed, and a high specific surface area of 217 m2 g-1 was maintained even after calcination at 500°C for 1 h. Sintering of the calcined powder at 550°C for 3 h resulted in a decrease in specific surface area to 157 m2 g-1 in the case of the PA-treated powder, but the usefulness of the PA treatment to restrict the growth of TiO2 crystallites was again confirmed. Sensitivities of the sensor fabricated with the PA-treated powder to H2 and CO was not so high as those of the sensor fabricated with the untreated powder, irrespective of its high specific surface area, small crystallite size and ordered mesoporous structure involved. Thus, the PA treatment was effective for restricting the crystallite growth and then for maintainig the ordered mesoporous structure, but it may result in inactivation of surface sites for gas detection.

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  • Takeo HYODO, Yoshiaki TOMINAGA, Takashi YAMAGUCHI, Akihiko KAWAHARA, H ...
    2003 Volume 71 Issue 6 Pages 481-484
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    NOx sensing properties of semiconductor heterolayer sensors fabricated by slide-off transfer printing have been investigated. A WO3 single layer sensor showed much higher sensitivity to NO2 than that to NO. Loading of Ru or Pt on the surface of WO3 led to a slight improvement of both the sensitivity and the response speed to NO, but the response speed to NO2 was decreased especially by the Ru loading. In contrast, loading of Au improved notably the sensitivities and the response behavior to both NO2 and NO. Stacking of a 0.5Pt-Al2O3 (0.5 wt% Pt-loaded Al2O3) layer over a 0.5Au-WO3 layer showed little effect on the NOx sensitivities, whereas double or triple stacking resulted in a remarkable enhancement of NO and NO2 sensitivities at 350°C. However, the NO2 sensitivity of these sensors was superior to the NO sensitivity. On the other hand, the NO2 sensitivity of WO3 was decreased by the stacking of a Pt-Al2O3 catalyst layer, whereas the NO sensitivity increased. Such changes in NOx sensitivity became more significant when the loading amount of Pt in the catalyst layer increased from 0.5 to 1.0 wt%. As a result, it was found that the 1.0Pt-Al2O3/WO3 heterolayer sensor exhibited comparable sensitivity to both NO2 and NO at 350°C.

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  • Hiroshi IMAYA, Toru ISHIJI, Masayuki NAKANO, Mitsuo TAKAHASHI, Katsuo ...
    2003 Volume 71 Issue 6 Pages 485-489
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    An amperometric sensor based on pH-dependent electrode reaction of RuO2 electrode for the detection of acidic and basic gases has been developed. The sensor shows good characteristics of the response and stability for the sensing of CO2 and NH3. The detection mechanisms of the sensing reactions were studied by using different pH buffer solutions and X-ray photoelectron spectrometry (XPS). The response currents were hardly observed for acidic and basic gases, such as CO2 and NH3, respectively, by using the sensor containing a pH buffer solution. The steady current is concerned with variation of pH of buffer electrolyte. By measuring the XPS spectrum of RuO2 electrode surface after acidic or basic gas flowing, the changes of the oxidation states of RuO2 was observed. The results proved that the detection mechanism of the sensor is based on the pH dependent electrode reaction of RuO2 which response current is determined by the concentration of hydrogen ion or hydroxide ion induced by acidic and basic gases.

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  • Kazunori IKEBUKURO, Yoko SAITO, Satoshi IGARASHI, Koji SODE
    2003 Volume 71 Issue 6 Pages 490-495
    Published: June 05, 2003
    Released: August 30, 2019
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    Genetically engineered thermostable pyrroquinoline quinone glucose dehydrogenase (S415CGDH) was used for labeling probe DNA and amperometric DNA sensor was constructed and utilized for the detection of PCR amplified Salmonella virulence invA gene. The invA gene from Salmonella which accounts for many cases of food poisoning was targeted and the DNA bearing a specific sequence complementary to the invA gene was immobilized onto an Au electrode as a capture DNA S415CGDH labeled probe DNA was hybridized with the immobilized DNA at 60°C for 10 min and then the resulting electric current generated from S415CGDH by glucose addition was measured. The electric current was obtained when S415CGDH was used for labeling probe DNA but not when the native enzyme was used. The sensor response increased with the addition of glucose and 4.0 × 10-9 M of the S415CGDH labeled target DNA was detected in the presence of 29 mM glucose. The detection of PCR product was also investigated and it was successfully detected using asymmetric PCR product with sandwich method.

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  • Kenji OBATA, Kengo SHIMANOE, Norio MIURA, Noboru YAMAZOE
    2003 Volume 71 Issue 6 Pages 496-502
    Published: June 05, 2003
    Released: August 30, 2019
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    A solid state CO2 sensor operative at room temperature, developed by incorporating a metal oxide sensing electrode and a metal carbonate auxiliary phase into a NASICON (Na3Zr2Si2PO12)-based electrochemical cell, suffers from a humidity-dependent shift of the EMF response to CO2. In an attempt to reduce the humidity dependence, binary carbonate systems of Li2CO3-BaCO3 and Na2CO3-BaCO3 at various compositions were tested for the auxiliary phase of the device. The melting-and-quenching method conventionally used for attaching the carbonate was not applicable well to the present type device due to the corrosion of NASICON surface. The humidity-least dependent device could be obtained when the Li2CO3-BaCO3 composite (1:2 in molar ratio) was adhered to NASICON by calcination at 500°C (non melting method). The device could respond to 300-3000 ppm CO2 quite well almost independent of relative humidity (RH) beyond 30%. In the lower range of RH, however, the EMF response commenced to shift and the CO2 sensing capability was completely lost in the dry atmosphere. A planar type CO2 sensor was fabricated successfully, which could work stably under the conditions of 30% RH and above.

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  • Seiji NAKATA, Kengo SHIMANOE, Norio MIURA, Noboru YAMAZOE
    2003 Volume 71 Issue 6 Pages 503-507
    Published: June 05, 2003
    Released: August 30, 2019
    JOURNALS OPEN ACCESS

    A field effect transistor (FET) device fitted with a WO3 layer over the gate area exhibited almost ideal FET behavior at 150 and 180°C in air containing various concentrations of NO2. Under the conditions of fixed source-drain voltage (3.0 V) and fixed drain current (450 μA), the gate-source voltage (VGS) was found to increase linearly with an increase in the logarithm of NO2 concentration over the range of several tens to 700 ppb NO2, proving its potentiality to work as an environmental NO2 sensor. However the times of 90%-response and -recovery to switching-on and -off 50 ppb NO2 were as long as 10 and 25 min even at 180°C, respectively. Cross sensitivity test revealed that the device was totally insensitive to CO2, but rather sensitive to NO. Water vapor was found to give a serious disturbance to the device: The Vgs response to NO2 as well as its dependence on NO2 concentration changed with a change in relative humidity.

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