Vol. 30, Supplement B (2014)

1.

We examined the sensing behavior of metal element (Fe, Co, Mn, V, La, Sm, Mo, Pb)-loaded SnO₂ semiconductor sensors for ethanol, methylethylketone and toluene detection at 400 and 600oC. The sensitivity at 400oC was higher than that of 600oC. At 400oC, La-loaded SnO₂ sensor showed the highest sensitivity to methylethylketone, and at 600oC, Sm-loaded SnO₂ sensor showed the highest sensitivity to methylethylketone. For almost all sensors, the sensitivity to ethanol and methylethylketone was higher than that of toluene. However, at 400oC, the sensitivity of V-loaded SnO₂ sensor was in order of toluene > ethanol ≈ methylethylketone. The recovery time was much less than the response time, and this behavior was quite noticeable at 400oC. The response and recovery time of the sensor are limited by surface adsorption and desorption. The thermal desorption spectroscopy was used to study desorption behavior of VOC on the SnO₂ surface.

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2.

SnO₂ and Pd-loaded SnO₂ MEMS sensors were prepared and their gas sensing properties to 200ppm H₂ were investigated in dry and wet atmosphere by continuous heating and pulse heating methods. The sening film was deposited by injection method on a MEMS type device with micro heater and electrode. Pd-loaded SnO₂ MEMS sensor showed a good sensing performance to H₂. However the sensor response was reduced by pulse heating at 400°C, maybe due to the low amont of oxygen speices on the surface at such low temperature.

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3.

Neat and Pd-loaded WO₃ sensors were prepared from a kind of lamellar-structured nanoparticles. The sensing properties and mechanism for reducing gases, H₂, CO and CH₄ were investigated. It was found that the sensor response of reducing gases was greatly improved by Pd-loading. It was also observed that the sensing process of neat and Pd-loaded WO₃ sensors demonstrated a different dependence on oxygen. For Pd-loaded WO₃, the sensing process showed a weak dependence on oxygen and became independent of oxygen at the low concentration of oxygen. In contrast, the sensing process of neat WO₃ showed oxygen-dependence at all concentrations. For CH₄, both sensors showed an oxygen-dependent sensing process. It was concluded that Pd-loading activated the surface lattice oxygen, which involved the sensing process of H₂ and CO.

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4.

　We have been studying the mechanism of the low power semiconductor CO sensor. In this paper we report the practical development of the sensor for CO alarm. This sensing element can adsorb CO with positive charge during non-heating period. The 0.01mW of lower power consumption (on average) is achieved since the CO detection capability during non-heating period for 1 hour. When CO concentration increases, sensor heat cycle shifts to a shorter period with 1 minute cycle to detect CO accurately. The particle size of sensing materials (The Pd doped SnO₂) is controlled in a nano size to provide a densely-packed sensing element, which is effective to stabilize the CO sensitivity when the sensor is used in high-humidity environment. Also, we have successfully improved the stability by applying an aging condition for acceleration. This CO sensor has relatively high hydrogen sensitivity, so that we have studied a new compensation method. A new algorithm judges the presence of hydrogen by monitoring the changes of sensor resistance pattern during the heating period. We have monitored the performances of this CO sensor in actual alarm devices for 2 years, and we have confirmed that this method is effective for commercial applications.

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5.

We have developed a micro methane sensor obtained by laminating “nano-columnar structure SnO₂ thin film" and catalyst layer on the circular diaphragm support layer with a built-in thin film heater. Ultra-low power consumption (0.06mW) required for 5-year battery operation was achieved by separating the functional elements of gas sensors, optimizing the materials and structures in charge of each function, microminiaturizing, and driving with low power ultra-short pulse. Furthermore, this sensor has realized higher sensitivity and higher selectivity than conventional methane sensors.

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6.

We have developed a micro methane sensor for the practical use of battery driven gas leak alarm. It was difficult to reduce a power consumption of methane sensor and to stabilize the sensor performance in practical circumstances. We have broken through the difficulties mainly owing to the MEMS (Micro Electro Mechanical Systems) technology and a new original catalyst. Fuji Electric has established a design technique, manufacturing process, and analytical methods for the MEMS sensor. Long-term reliability of the sensors improved by the new catalyst has been verified by a large scale field test.

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7.

Characterization for structure of Sn_1-xPt_xO₂ thin film produced by sputter deposition was investigated, which showed high selectivity and long life time as gas sensor. XRD (X-ray diffraction) and XAFS (X-ray Absorption Fine Structure) showed that Sn_1-xPt_xO₂ has a rutile structure similar to SnO₂ at less than x = 0.27 where Pt ion was located at the Sn position in the rutile structure. The Sn_1-xPt_xO₂ became amorphous at greater than x = 0.30. And we have demonstrated by in-situ XAFS that Sn_1-xPt_xO₂ at less than x = 0.27 was maintained as rutile structure even the atmosphere of gas sensor driven under reduction gas of 430 deg C.

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8.

A novel sensor for organic floating particles such as pollen and mold spores has been developed using semiconductor thin-film. The sensing film has a double layered structure; the first and second layers are Fe₂O₃-based and SnO₂-based thin film, respectively. Pt-based film is deposited as sensor electrodes. The films are deposited on an alumina substrate. The sensor resistance steeply decreases and recovers to the initial value within about 10 s when a grain of pollen or mold spores adheres to the surface of the sensing film and burns on it. The amount of the decrease of the resistance, the response time and recovery time depend on the size of the organic floating particles. Thus it is possible to determine the species of the particle by the developed sensor. The repeatability of the sensor response is satisfactory.

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9.

A catalytic combustion-type carbon monoxide gas sensor operable even at low temperatures was developed by incorporating a Pt-loaded CeO₂–ZrO₂–SnO₂ catalyst and aluminum nitride as the CO oxidizing catalyst and the intermediate heat transfer layer, respectively. Since the Pt-loaded CeO₂–ZrO₂–SnO₂ catalyst can completely oxidize CO at 65°C and the aluminum nitride can effectively transfer heat to Pt coil, the response to CO drastically accelerated even at the temperature as low as 70°C and the quick response was realized compared with the previously reported sensor without aluminum nitride.

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10.

To investigate the effect of pore structure of Al₂O₃ supported Pd catalysts for combustion type gas sensor application, the physical properties (BET surface area, pore volume, pore size distribution, Pd dispersion), catalytic activity for CO oxidation and the heat of CO oxidation were evaluated. The relationship between catalytic activity and oxidation heat of Pd/Al₂O₃ catalyst has suggested that the Pd catalyst supported on non/less porous Al₂O₃ was suitable for the effective conduction of the oxidation heat. The simultaneous achievement of high catalytic activity and thermal conductivity on non/less porous supports are important for the combustion-type sensor with high sensitivity.

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特別講演

Our company has been proposing various gas sensor technologies for life safety, security, and comfort throughout the world. Among them, we have supplied the bulk type semiconductor gas sensors, TGS109 and TGS203 for combustible gas detectors in Japan, and for CO detectors in North America since the dawn of each market respectively. Then we have further developed and have been supplying the micro-bead type semiconductor gas sensor TGS3870 and the electrochemical gas sensor TGS5042 to meet changes in market requirements. We will introduce the next generation of gas sensors which are currently under development; TGS8410 MEMS type semiconductor gas sensor and TGS5141 electrochemical gas sensor.

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11.

A solid electrolyte-type planar gas sensor using NASICON (Na₃Zr₂Si₂PO₁₂) disc attached with Pt mixed with 1 wt% Bi₂O₃ as a sensing electrode and a Pt counter electrode was fabricated, and then the CO-sensing properties were investigated at the operating temperatures of 25~300ºC. The CO response of the sensor was small at 300ºC in N₂ mixed with 0~20% O₂. A drop in the operating temperature to 100ºC enhanced the CO response only in N₂ containing O₂ less than 5%, but the response behavior was instable. On the other hand, the sensor showed relatively large and stable CO response at 25ºC in N₂ mixed with 0~20% O₂, though the recovery speed was slow in N₂ and the EMF in base gas slightly shifted to a negative value after exposure to CO. The response of the sensor to inflammable gases was much smaller than that to CO, especially at 25ºC. The introduction of moisture into synthetic air reduced the CO response, but the sensor could detect 1 ppm CO, even in wet synthetic air (30%RH). In addition, an increase in humidity in synthetic air improved the CO selectivity against H₂ at 25ºC.

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12.

Yttria-stabilized zirconia (YSZ)-based gas sensors attached with each of oxide sensing-electrodes (SEs) were fabricated and examined for sensitive and selective detection of H₂. Among nine kinds of oxides tested, Ta₂O₅ was found to give insensitive responses to various interfering gases. Since it has been reported so far that the addition of a small amount of noble-metal nanoparticle to an oxide-SE is rather useful for improving sensing characteristics to a particular gas, we have tried here to enhance hydrogen responses by the addition of several noble-metal nanoparticles to Ta₂O₅-SE. As a result, among the six noble-metal nanoparticles examined, Au nanoparticles gave a significant increase in the H₂ sensitivity. It was also found that the YSZ-based sensor using the Ta₂O₅( + 1 wt.% Au)-SE showed relatively high selectivity to H₂. In addition, the sensitivity of the present sensor varied almost logarithmically with the H₂ concentration in the range of 20 – 800 ppm at 500oC even in the presence of 5 vol.% H₂O.

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13.

To develop a stable potentiometric VOC sensor, a planar type zirconia based sensor with Pt/YSZ electrodes was fabricated and then one side of the electrode layer was modified with Ti or Zr oxide. The sensor with the modified Pt/YSZ electrode is sensitive to several VOCs and the sensitivity decreased with an increase in the operating temperature from 400oC to 600oC. The sensitivity is in a sequence of methylethylketone > ethanol > toluene. The concentration dependence of the electrode potential is experimentally expressed with E=aC1/m. A higher detectability was confirmed for the sensor with Ti-loaded Pt/YSZ electrode. The loading effects on the recovery of the electrode potential to the base line in uncontaminated air were discussed with an aid of a thermal programmed desorption behavior of adsorbed/decomposed chemical species.

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14.

Many oxides were examined here to search an excellent sensing-electrode (SE) material for a new-type impedancemetric yttria-stabilized zirconia (YSZ)-based O₂ sensor. First, Nyquist plots of the obtained sensors were measured at 600°C in air or in various gases diluted with air. As a result, among the oxides tested, several perovskite oxides were found to give almost insensitive responses to various reducing/oxidizing gases which usually exist in automotive exhausts. Then, Nyquist plots of the sensors using each of the above-mentioned oxides-SEs were measured at 600°C in different O₂ concentrations. In the case of a specific oxide, the absolute value of impedance at a fixed frequency was found to increase largely with decreasing O2 concentration in the whole frequency range examined. On the other hand, a small change of impedance value in the lower frequence range was only observed in the case of Pt-SE, when the O2 concentration was varied. Moreover, the response of sensor using the specific oxide-SE was confirmed to be relatively quick in the O2 concentration range of 0.05 - 21 vol.% at 600°C. Therefore, it is concluded that the selected perovskite oxide could be used as one of attractive SEs for a new-type impedancemetric YSZ-based O₂ sensor.

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15.

Effects of the surface coating of the Pd-Pt electrodes with ethylene-vinylalcohol copolymers (EVOH) on the H₂-sensing properties of the diode-type gas sensors using an anodized TiO₂ film and Pd-Pt electrodes (Pd-Pt/TiO₂) have been investigated at 50~150°C in air or N₂ under dry or wet atmosphere. H₂ response of all the EVOH-coated Pd-Pt/TiO₂ sensors was slightly smaller than that of the uncoated Pd-Pt/TiO₂ sensor in air, and the magnitude of the H₂ response in air decreased with an increase in the thickness of the EVOH film coated. However, the EVOH coating on the Pd-Pt/TiO₂ electrodes largely reduced the influence of moisture on the H₂ response in air, probably because the EVOH film inhibited the adsorption of water molecules on the electrode surface. In addition, H₂ response of all the sensors showed quite-low dependence on humidity in N₂, especially at 150°C. On the other hand, the surface coating with some kinds of EVOH was effective in reducing oxygen dependence of H₂ response of the Pd-Pt/TiO₂ sensor, only under dry atmosphere.

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16.

As non-invasive human bio-monitoring, a breath ethanol imaging system using biochemical luminescence has been developed. The breath gas imaging system has capability to evaluate ethanol metabolism performance as easy, rapid and painless approach. The visualization system provides information of ethanol distribution based on the chemiluminescence (CL) image on an enzyme-immobilized mesh. The spatio-temporal changes of CL generated by ethanol in exhaled breath after ethanol oral administration was detected by employing an electron multiplier CCD camera. The breath samples of volunteers with aldehyde dehydrogenase 2 (ALDH2 [+] and ALDH2[-]) were supplied for the imaging system. The exhaled breath ethanol obtained from volunteers were analyzed over a period of 120 min after oral administration of alcohol 0.4 g/kg body weight. A peak of exhaled breath ethanol concentrations of ALDH2[+] and ALDH2[-] appeared at 30 min after drinking, and then breath ethanol concentration was gradually decreased as alcohol degradation by drug-metabolizing enzymes (i.e. ADH, ALDH2). The imaging system allows us to apply non-invasive methods in exhaled breath for the assessment of ethanol metabolism.

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17.

Previous our study, electrochemical gas sensor for acidic gas detection have developed using Pt nano particles and carbon hybrid electrode. The electrode with Pt particles of nominal size 5 nm embedded in carbon layer was prepared by the unbalanced magnetron sputtering method, with which Pt & C were simultaneously sputtered onto polytetrafluoroethylene gas permeable membrane. The sensor showed good characteristics of high sensitivity and fast response for the sensing of HBr and HCl with low interference from coexistence gases such as H₂. The good long term stability of HBr was obtained for 1 year. On the other hand, response current for HCl was decreased for long time usage. In this study, we tried to improve the long term stability for HCl. In order to reduce oxidation state of Pt, applied potential of the sensor was intermittently changed to negative side. As a result of this potential change, the response current for HCl was kept for a half year compared with initial response current.

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18.

We have been developing several CCD-type ion image sensors with vast numbers of array sensing pixels. The image sensor is a useful tool to observe extracellular ion response of living cells or a tissue by stimulation . The ion image per 0.03 s can be obtained. However, pH-time response of the CCD pH image sensor was not evaluated enough until now. The measurement of accurately velocity of ion releasing and/or ion absorption of living cells requires its pH-time response, or time constant. Previously, we reported a flow-though cell that can be easily installed and uninstalled to the CCD pH image sensor. Although the system can exchange different solutions smoothly, it was inadequate for fast　exchange of the solutions. In this study, we examined the pH-time response using a spout of aqueous solution by syringe pressurization in open system. The exchange rate was very fast at partial sensing pixels in the sensor. Then, we evaluated time constant of these sensing pixels at different pH solutions by a fast exchange of buffering solutions to pH = 1.

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19.

It is known that nitrate is one of stress markers in saliva. In this report, we describe a new nitrate sensor based on an extended-gate type organic field effect transistor (OFET). The nitrate sensing part of OFET is the extended-gate electrode modified with nitrate reductase. In an attempt to detect nitrate in an artificial saliva, we observed a threshold voltage shift in the OFET with increasing the nitrate concentration. The detection limit for nitrate was 700 ppb. We believe that these results could open up an avenue for development of future organic transistor-based sensors for human stress.

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20.

As part of our ongoing program to develop organic field effect transistor (OFET)-based sensors for health care, we report a histamine detection method using an extended-gate OFET. Histamine is contained in spoiled fish, which causes foodborne illness known as scombroid poisoning. The new OFET possesses an extended-gate functionalized by carboxyalkanethiol that can interact with histamine. As a result, we have succeeded in detecting histamine in an aqueous solution through a shift of threshold voltage. On the other hand, the addition of histidine did not induce significant changes in the electrical characteristics of the OFET. This indicates the potential utility of the designed OFET for food freshness sensing.

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21.

A termination-controlled boron-doped polycrystalline diamond electrolyte solution-gate field effect transistor (BDD-SGFET) for the use of pH sensor has been investigated. We have studied a non-doped diamond field effect transistor where a hydrogen-termination induces p-type semiconductor property without extrinsic doping. The channel was directly wetted to liquid and the device was employed as so-called electrolyte-solution-gate field effect transistor (SGFET) sensor. Here, we propose a termination-controlled BDD-SGFET. The SGFET I-V characteristics were evaluated with bias voltages within potential window of diamond. The Ids-Vds characteristics showed pinch-off and saturation. In addition, partially oxygen- and fluorine-terminated BDD-SGFET was obtained by oxidation/fluoridation treatment. The oxygen-terminated BDD-SGFET possessed pH sensitivity of 15 – 50mV/pH, whereas the fluorine-terminated BDD-SGFET possessed 4～30mV/pH.

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22.

Sensitive detection method for nitrite-ions needs to control of eutrophication in close water system. In this study, it was aimed to develop a high sensitive electrochemical nitrite- ion sensor with perovskite-type oxide-modified nanoporous Au (np-Au) electrodes were investigated. Perovskite-type oxide SmFeO₃ powder was prepared by a polymer precursor method. The np-Au electrode was prepared by square wave potential pulse treatment in NaOH solution. SmFeO₃ thick-film was deposited by an electrophoretic deposition (EPD) method on the np-Au electrode. Among the sensor devices tested, the SmFeO₃ np-Au electrode based sensor showed linear response to nitrite-ion between 1.0×10-5 M and 6.0×10-3 M with good selectivity. The sensor response properties were influenced by the configuration of electrode surface.

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23.

We have previously proposed enzyme-sensors that combined oxidase reactions with the 2D-SPR imaging of the Os polymer-redox state in order to develop bio-sensors that can detect bio-markers for metabolic disorders more easily and faster than the conventional methods. For example, lysine or galactose sensing using lysine oxidase(LysOx) or galactose oxidase(GalOx), respectively was already reported. In this study, we aimed to develop a multi-enzyme sensor capable of the simultaneous detection of lysine and galactose by means of co-immobilizing LysOx/Os-HRP polymer spot and GalOx/Os-HRP polymer spot adjacently on the gold chip which is divided into two regions. In addition, we also attempted to detect three or more bio-markers simultaneously by this 2D-SPR imaging-enzyme sensor strategy.

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24.

We report here the orientation effect of antigen immobilized on the various alkanethiol monolayers in relation with clenbuterol sensing performance by using indirect competitive inhibition immunoassay. In our previous work, we found that the solution concentration used in self-assembly process highly affected on the monolayer structure. The orientation and the concentration of antigen were highly depended on the solution concentration. Here, in order to clarify the orientation dependence, we investigated here three types of alkanethiol compounds; (1) Dithiobis(succinimidyl)undecanoate (DSU); single chain cross linker attributed with a high orientation; (2) Carboxy-EG6-undecanethiol (CEG₆); a flexible armed molecular structure; (3) Dendrimer thiol, dithiobis(C₂-NTA), three-branched molecular structure. To detect clenbuterol by indirect competitive inhibition immunoassay, clenbuterol was immobilized on the end group of thiol compound monolayer. As a result, dendrimer C₂-NTA sensor surface reveals the highest sensitivity among those sensor surfaces, represented by limit of the detection (LOD) value at 10 ppt. The sensor surface structures were characterized by the electrochemical reductive desorption curve, STM observation and FT-IR. For multiple analyses, 0.1 M NaOH was injected for surface regeneration. One immunosensor surface could be used for >100 times analyses. The detection process was very rapid which is only 1000 s for one immunoreaction–regeneration cycle.

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25.

We present the development of an immunosensing system to measure simultaneously immuno-complexes formed on PDMS substrates by using the bio-LSI system. Line patterns with anti-mouse IgG antibody and anti-human IgG antibody were prepared on PDMS substrate. After the substrate was treated with the solution containing BSA to prevent a nonspecific adsorption, another PDMS with microchannels were mounted on the PDMS substrates by rotating with 90 relative to the line patterns of antibodies. The solutions containing model analytes (mouse IgG and human IgG) were introduced into each channel to form the immuno-complex at the intersections. The PDMS substrates were then treated with glucose oxidase (GOx) labeled antibody. The PDMS substrates with intersections of immuno-complexes were mounted on the bio-LSI chip immersed in the solution containing 20 mM glucose. Potential (+0.7 V) was applied to all electrodes in bio-LSI to oxidize hydrogen peroxide generated by the enzyme reaction of GOx. The each area with high oxidation currents of hydrogen peroxide coincided with the locations of intersections. Bio-LSI systems afford current images on the activities of captured label (GOx) for the simultaneous immunosensing.

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26.

Nitrogen-containing carbon alloys (NCCAs) were found to have catalytic activity similar to that of biological enzyme catalase. The NCCAs were fabricated by stepwise electrolysis as follows. First, a carbon felt was electro-oxidized in ammonium carbamate aqueous solution at +1.1 V (vs. Ag/AgCl) for 60 minutes. Then, this carbon felt was reduced in 1.0 M sulfuric acid at -1.0 V (vs. Ag/AgCl) for 20 hours at room temperature. One of the introduced functional groups was expected to be a hydrazino group that must be oxidized by air. The oxidized species of a hydrazino group work as the catalase-like catalytic active sites of hydrogen peroxide.

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27.

In this study, we have developed non-enzymatic glucose sensor by utilizing manganese(IV) oxide (MnO₂) modified electrode, prepared by electrolytic deposition method. At the MnO₂ modified electrode, glucose is electrochemically oxidized in the near-neutral pH electrolyte solution (pH 8.0) due to its electrocatalysis ability. In order to detect glucose in the analyte selectivity without any electrochemical interferences such as ascorbic acid, we covered the electrode with polyion complex (PIC) layer. The PIC-covered MnO₂ electrode exhibited high improvement concerning glucose selectivity. In addition, we employed not only glucose but also 2-deoxyglucose to examine effects of the molecular structure of monosaccharide on resultant electrochemical response for the MnO₂ modified electrode. We presumed that chemical reducing ability of saccharide depends on its molecular structure, i.e., presence or absence of hydroxyl group at C₂.

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28.

The electrochemical activities of binary metals in a Pd–Nb system were investigated as a function of their compositions, crystal structures, using a hydrogen peroxide (H₂O₂) and ascorbic acid (AA) redox reaction. High activities for the redox reaction of H₂O₂ were observed when an alloy of composition 75 atom % Pd–25 atom % Nb (Pd–25Nb) with Pd₃Nb phase was used. Tests on six electrodes of Pd–25Nb, Pd, Pt, Pd–10Nb, Pd–30.8Nb, Pd–54.4Nb showed that at a constant potential of 0.7 V, the Pd–25Nb electrode had the best H₂O₂ detection capability among them. And then, Pd–25Nb gave the best performance in terms of preferential H₂O₂ against AA. Subsequently, the Pd–25Nb, Pd and Pt were used for the fabrication of amperometric glucose sensors. To fabricate the glucose sensors, we formed the three electrodes first with γ-aminopropyltriethoxysilane layer, and then with enzyme layer immobilized glucose oxidase. Tests on the Pd–25Nb, Pd, and Pt electrode glucose sensors showed that the Pd–25Nb glucose sensor had a better glucose detection capability than the Pd and Pt glucose sensors.

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29.

We have developed two electrochemical apoptosis sensing methods based on the detection of caspase-3 activity. One is a method using Asp-Glu-Val-Asp-p-nitroaniline (DEVD-pNA) which is conventionally used as a colorimetric substrate for caspase-3. We detected free pNA released from DEVD-pNA by the caspase-3 activity using differential pulse voltammetry. Both DEVD-pNA and pNA show a reduction current peak between −0.74 V and −0.75 V vs. Ag/AgCl. However, the reduction peak current per unit concentration of pNA is 7.3 times higher than that of DEVD-pNA. Therefore, the peak current increased with the concentration of pNA released from DEVD-pNA. The other is a method using DEVD-p-methoxyaniline (pMA) newly synthesized for amperometric detection of caspase-3 activity. From results of the cyclic voltammetry, we employed 0.55 V vs Ag/AgCl for the applied potential of amperometry, because pMA is oxidized at this potential while DEVD-pMA is not. With both methods, we successfully detected the apoptosis of the human liver carcinoma cell line. These electrochemical sensing methods can be applied to easy and on-site monitoring of the cell viability in wide fields of bioscience and medicine including transplantation therapy and drag discovery.

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30.

Fluorescence sensing of the interaction between model biomembranes with different lipid composition and endocrine disrupting chemicals (EDCs) was carried out by using a liposome-encapsulating carboxyfluorescein (CF-liposome). We detected a significant increase in fluorescence intensity in CF-liposome solutions due to the leakage of CF caused by the interaction of EDCs with the biomembranes of liposomes. The temporal increases in fluorescent were significantly different among the lipid compositions of CF-liposome and the EDCs. Results were considered by summarizing the interactions in radar charts and by showing the pattern of interaction of each EDC. Each chart showed a dissimilar pattern reflecting the complexity of the biomembrane-EDC interaction. The results indicate that this fluorescence sensing could be useful to evaluate the interaction.

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31.

We developed an electrochemical lipopolysaccharide (LPS) detection system by using an ultraflat nanocarbon film electrode formed by employing the unbalanced magnetron sputtering method. The electrode was modified with poly--lysine (PL) by chemically or physically modification to trap LPS on the electrode surface. LPS sample was cast on the modified electrode, and then a polymyxin B-ferrocene conjugated molecule (PMB-Fc) was captured on the LPS adsorbed electrode via the LPS-PMB affinity interaction. The adsorbed PMB-Fc provided an amplified response with Fe²+ ions, and the current response was dependent on the amount of captured LPS (LOD=2.0 ng/mL). This was due to the efficient accumulation of the obtained current for LPS and the very low noise made possible by the ultraflat surface. Moreover, the nanocarbon film electrode surface was modified with other atoms including oxygen or fluorine to improve the sensing performance as regards increasing electrode activity of PMB-Fc and noise reduction. We found that the fluorine modification gave the superior signal-to-noise current due to the decreasing the background noise level.

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32.

A nanocarbon film electrode was used to analyze a simple DNA analysis technique. The film was formed by using the unbalanced magnetron (UBM) sputtering method that provided a nanocrystalline sp2 and sp3 mixed bond structure with an atomically flat surface (surface roughness of ca. 0.3 nm). This film electrode has excellent properties including a wide potential window, low background current and little surface fouling while maintaining relatively high electrode activity for various biomolecules. These characteristics allow the detection of biomolecules with high oxidation potentials. As a result, this film electrode can measure all the DNA bases (including the DNA base derivatives e.g., 5’-methylcytosine and 8’-hydroxy 2’-deoxyguanosine) more quantitatively than conventional carbon-based electrodes. Here, we will discuss the electroanalysis of damaged ATP molecules induced by various radiations (X-rays, soft X-rays, or γ-rays) by using the UBM nanocarbon film electrode.

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清山賞受賞講演1

I have developed a highly accurate urine glucose sensor employed with three electrodes and multi-layered membranes, and been researching redox characteristics of super refractory binary alloys based on platinum group metals applying for an amperometric biosensor. Characteristics of the urine glucose sensor showed that: unsusceptible to interference species such as ascorbic acid, acetaminophen, and uric acid; long term lifetime stability of 66 days; high measurement accuracy of 0.985 (n=30) to diabetes urine samples. Furthermore, we have achieved a large-scale production of the glucose sensor as improving adhesion strength among the multi-layered membranes. 82 urine glucose sensors fabricated on a single glass wafer showed acceptably low dispersion, relative standard deviation of 42.9% (n=82). Concerning the redox characteristic researches of the binary alloys, it was found that a palladium-niobium binary alloy could be used an amperometric biosensor’s transducer material instead of platinum.

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清山賞受賞講演2

The chemical imaging sensor is a semiconductor-based electrochemical sensor that can visualize the two-dimensional distribution of pH or the concentration of a specific chemical species in the sample solution. It is based on the principle of the light-addressable potentiometric sensor (LAPS), in which the variation of the Nernst potential on the sensing surface is read out in the form of a photocurrent induced by illumination. Recent developments of the LAPS-based chemical imaging systems are summarized and discussed in terms of spatial resolution, precision, measurement speed, movie recording, miniaturization and application to microfluidic devices. Prospective applications are expected in various fields, which take advantage of label-free measurement, stepless zoom, large sensor area and low cost.

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33.

We have developed various types of oxygen sensors by using an oxygen sensitive fluorescence dye, ruthenium complex. We have also succeeded in optical imaging of oxygen distribution in a Y-shaped micro flow channel. In this study, the oxygen sensing membrane was prepared on a flexible polymer film, and oxygen distribution on the surface of 3D-structure was visualized. Nafion solution containing ruthenium complex was spread between two polymer films, oxygen permeable polyethylene/ polypropylene laminated film (PE/PP film) and oxygen non-permeable polyvinylidene chloride film (PVDC film). The prepared oxygen imaging sheet could detect difference of oxygen concentration. The control imaging sheet whose fluorescence intensity is independent from oxygen concentration was also prepared with an oxygen sensor film and two PVDC films. By using these two sensor sheets, oxygen distribution on the surface of a germinated seed could be successfully visualized.

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34.

We present a novel system for monitoring of microcolony formation based on wide-field imaging. Bacterial microcolonies were cultured on a micro-agar plate placed directly on top of a complementary metal oxide semiconductor sensor. The micro-agar plate was illuminated by a blue light emitting diode, and then imaged by the sensor without any imaging lenses. In the acquired images, the diffraction patterns derived from the microcolonies were recorded. This system allowed simultaneous tracking of multiple microcolonies over the wide field of view. Furthermore, the difference in growth rate of the microcolonies was observed among the micro-agar plates containing various concentrations of antibiotics. This system is expected to provide a high-throughput colony assay for investigation of bacterial inhibitors.

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35.

An electrode grafted molecularly imprinted polymer (MIP) works as highly selective, and sensitive sensor by using change in permeability of redox solute in the MIP layer induced by site specific interaction with the template. The sensitivity of the gate efect is so high that it is advantageous for mircrosensing. For taking the advantage of the gate effect, we prepared a glass needle electrode on which ITO was deposited and MIP was grafted. Glass rod (1 mm in diameter) was pulled under heating to make sharp tip (ca. 100 μm in diameter). The sharpened glass rod was soaked in toluene in which ITO particle was dispersed. The glass rod was baked to form electrically conductive layer. Diethyldithiocarbamate benzyl group, which is initiator of radical polymerization, was introduced on the surface of the ITO layer. Methacryloxyethyl trimethylammonium chloride, acrylamide, and methylene bisacrylamide was copolymerized in the presence of the heparin template with grafting onto th! e ITO layer. A traditional cyclic voltammetry of potassium ferrocyanide was performed with the MIP-grafted microelectrode. The oxidative current of ferrocyanide was increased by the presence of heparin of 50 unit/mL. While, the current at the sputtered ITO grafted with the heparin-MIP was decreased by the heparin of the same concentration. The difference may be due to some difference between the chemical properties of the ITO layers generated by the sol-gel and the sputtering methods.

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36.

To realize autonomous efficient control of microfluidic transport in microanalytical devices, a simple valve consisting of a self-assembled monolayer (SAM) formed on a platinum electrode was developed. Because the SAM is hydrophobic, an electrolyte solution stops at the edge of the electrode formed in a flow channel surrounded by poly(dimethylsiloxane) (PDMS). However, by applying a potential to the electrode, the SAM is removed and the solution passes the underlying hydrophilic electrode area. The switching time could be reduced by reducing the length of the electrode along the flow channel. The valve could be used in various microfluidic devices for timely injection of solutions in flow channels located in the lower stream.

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37.

Drug susceptibility test for transplant therapy is indispensable to avoid rejection responses. However, the test is based on the counting of the number of lymphocytes and is time-consuming. To improve this point, measurement of the concentration of a cytokine secreted from lymphocytes can be a good alternative. To this end, we designed a microfluidic device for absorbance measurement with integrated optical components. Lenses and mirrors were formed with poly(dimethylsiloxane) (PDMS) using the difference in the refractive index between PDMS and air. A microfluidic structure to treat sensitive biomolecules was also incorporated to avoid denaturation. Enzyme linked immunosorvent assay (ELISA) was conducted on the chip. A linear relationship was observed between the absorbance and the concentration of cytokine. The activity of lymphocytes in whole human blood samples was also measured using the device.

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38.

To integrate fully electrophoretic microfluidics with electrochemical sensor system, we study fast separation conditions for inorganic ions using a miniaturized laboratory−built capillary electrophoresis (CE) system made from a conventional fused−silica capillary, a power supplier, a capacitively coupled contactless conductivity detector (C⁴D) and so on. We have investigated mechanically simple sample introduction-system, such as a continuous introduction and also a whole column introduction, although mechanically complex sample introduction-system, such as hydrodynamic or electrokinetic injection has been widely used in conventional CE. In case of the continuous sample introduction, 6 major anions were successfully separated within 1.5 min using an optimized electrophoretic running-buffer. The analytical validation was fairly good. The developed method was applied for the ion-analysis in tap water, river water, and so on. In case of the whole column sample introduction, 6 major anions together with 5 major cations were successfully separated within 2.5 min using an optimized electrophoretic configuration.

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39.

　Flow-injection determinations of bio-relatedcompounds using enzymes immobilized onto carbon fibers modified chemically were performed. Application of each of a disk type of the immobilized enzymes onto the supports was to each a flow-injection system, respectively. Performance characteristics of the systems were examined.

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40.

Tyrosinase (TYR) was physically adsorbed onto porous carbon felt (CF), a microelectrode ensemble of micro-carbon fiber and possesses a three-dimensional random structure, from mixed buffer solution of TYR and methylene blue (MB). MB in TYR solution was essential to obtain sufficient catalytic activity of adsorbed TYR. In contrast, without MB, the adsorbed TYR showed almost no apparent catalytic activity probably due to mainly adsorption-induced unfavorable conformational change (i.e., surface-induced denaturation). Simultaneous adsorption from mixed solution of TYR and MB was effective than the step-by-step adsorption. The TYR/MB-CF was successfully used as an electrochemical flow-through detector for sensitive and rapid consecutive determination of TYR-substrates (i.e., catechol and phenol compounds).

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41.

Enzyme glucose oxidase was immobilized on Pt wire electrode using cellulose dispersion solution produced by wet jet milling. Glucose oxidase was employed as enzyme and glucose sensor properties of obtained GOx-immobilized electrode were investigated. Cellulose dispersion solutions of 1.0 to 40 mg/L were used and all fabricated GOx-immobilized electrodes provided good response current. The introduction of inner films of γ-polyglutamic acid and cellulose acetate were efficient to obtain glucose sensor, which have low influence to electroactive compounds exist in biological fluid, such as ascorbic and uric acids. GOx-immobilized electrode prepared using cellulose dispersion performed good sensor stability after an initial response decrease on the first three days.

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