Vol. 30, Supplement A (2014)

1.

We have developed the technology to capture the cells expressing surface antigen from the cell population by dielectrophoresis (DEP). DEP device consisted of a upper ITO electrode and lower IDA electrode. A suspention of HL-60 cells treated with all-trans retinoic acid (ATRA) was injected into the DEP device immobilized with anti-CD13 antibody or anti-CD11b antibody. The application of AC voltage forced most of cells to form a line pattern on the gap region between the band-electrodes. Then, the voltage of band B was switched off, some of the patterned cells moved to the band B. Cell capture efficiency was defined as a ratio of the number of cells remained on the gap region compared to the initial number of cells on the gap region. When the cells were accumulated on the gap region modified with anti-CD13 antibody, cell capture efficiency decreased with day in culture in the presence of ATRA. On the other hand, the accumulation of cells on the gap region modified with anti-CD11b antibody gave rise to the increase of the cell capture efficiency. The results indicated that the up and down regulations of targeted surface antigens would be rapidly and simply determined by the present method.

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2.

Based on the substitutional stripping voltammetry (SSV) that is a high sensitive electrochemical measurement, we have developed a new measurement system employing a gel made from hydrophobic ionic liquid and polymer. Since a salt bridge and an auxiliary electrochemical solution were necessary to conduct SSV, the conventional measurement system was somewhat complicated. The problem has hindered the application of SSV in compact chemical sensors. A gel coating on the silver electrode could replace both the salt bridge and the auxiliary electrochemical solution. As a result, all electrodes for SSV could be prepared on a planar substrate and the amount of the sample solution was enormously reduced to only 30 μl. The conventional SSV consists of two electrochemical steps; pre-electrolysis and stripping. In order to shorten the duration of measurement, the potential shifts of the auxiliary electrode were monitored during the pre-electrolysis to skip stripping, maintaining the sensitivity equivalent to the conventional SSV.

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3.

Paper has been in considerable interest as the base of electrochemical devices because of low cost, good flexibility, good disposability. In this study, we fabricated a paper-based Ag/AgCl reference electrode by screen printing. A Ag/AgCl layer was formed on a paper surface, on which a water repellent was coated. Then, silver ink and a resist ink were printed in turn. On the back side of the paper, KCl was casted on the paper, and then the resist ink was formed on the paper. The inks were dried at each printing. The stability of the electrode was estimated by measuring the potential between the electrode and commercial sat.Ag/AgCl electrode in the 0.1 M Na₂SO4 solution, 0.1 M KCl solution and phosphate buffer solution. It was found that the potential of the screen-printed reference electrode was held constant at about 0 V over 5 days. In addition, the present reference electrode could be used within 1 min just after immersing a solution.

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4.

　We have developed liquid-junction-free sensing device to perform substitutional stripping voltammetry (SSV). This method is a type of stripping analysis which exchanges redox current to metal ion deposition. In general, SSV system requires a liquid junction and a bipolar electrode to keep the electrical conductivity. In this study, we used driving electrodes instead of the liquid junction. Driving electrodes were used to supply the voltage required to drive electrochemical reaction of redox species on the bipolar electrode. The coupling of the oxidation of p-aminophenole (pAP) and the reduction of silver ion was happen on each sides of the bipolar electrode. First, we applied 0.2 V-0.3V with driving electrodes connected to the potentiostat to explore the time dependency and the pAP concentration dependency of the accumulation amounts of Ag. Furthermore, we performed endotoxin detection as a demonstration. Endotoxin induces enzyme cascade reaction called Limulus amebocyte lysate (LAL) reaction which produces pAP at the last step of the reaction. As a result, we could detect endotoxin.

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5.

Biorecognition elements, such as enzyme and antibody, was immobilized on Pt-Ir wire electrode by the combination of electrodeposition and photopolymerization. Glucose oxidase (GOx) was employed as enzyme and glucose sensor properties of obtained GOx-immobilized electrode were investigated. Sensor sensitivity was significantly influenced by the procedure to prepare electrolytic solution for enzyme electrodeposition, which was considered to be due to the difference in enzyme dispersibility in solution. Methacrylates with functional group, such as epoxy and quaternary amine, were also used beside hexyl methacrylate and 1,6-hexandiol dimethacrylate, in order to introduce interaction between enzyme and entrapping polymer film.

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6.

Hemin (Hm) was physically adsorbed onto porous carbon felt (CF), a microelectrode ensemble of micro-carbon fiber and possesses a three-dimensional random structure. The Hm-adsorbed CF (Hm-CF) exhibited a well-defined redox wave that is due to Fe(III)/Fe(II) redox process in Hm. The Hm-CF displayed excellent electrocatalytic activity for the reduction of dissolved oxygen (DO). The Hm-CF was used as an electrochemical flow-through detector for sensitive and rapid consecutive determination of DO. Deoxygenated buffer solutions were used as a carrier at a flow rate of 8.0 ml/min at an applied potential of -0.2 V vs. Ag/AgCl, and highly reproducible cathodic peak current responses to DO were observed in the 0.72 to 13.3 mg/ml (0.02 to 0.41 mM) concentration range, with the maximum throughput of 170 samples/h. The electrocatalytic activity of the Hm-CF was reversibly inhibited by respiratory toxins such as cyanide and azide, which bind sixth coordination position of iron active center of Hm. The electrocatalytic DO reduction current at Hm-CF was modulated by the respiratory toxins in a concentration-depending manner, which enabled the electrochemical sensing of the respiratory toxins.

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7.

We have been developing a patterning method of electrodes on plastic sheets. Recently, we refined our method to enable soldering. According to this method, a reversal pattern of electrodes was laser-printed on a polyimide sheet, and Pt-Ag-Pt layers were deposited by electron beam (EB) evaporation. After deposition of metal layers, toner was removed by sonication in acetone solution, remaining target electrode pattern. The adhesiveness and conductivity of metal electrodes were favorable, and soldering was possible. A side from this method, a simple method to fabricate conductive electrode pattern has been developed using electroless plating of Ag instead of evaporation.

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特別講演

We have developed a bacterial immobilization technique using a polypyrrole film, which allows us to design and fabricate bacterial sensors of a new kind. Bacteria usually have negative charges at their cell surfaces and we have found that they are easily to doped into polypyrrole films. Interestingly, all the bacteria studied were vertically immobilized against the film surfaces to show good viability after the immobilization. Imprinted polymers using these bacteria-immobilized films were prepared by electrochemical overoxidation of the polypyrrole films, in which bacteria were used as templates. The sensors were fabricated on gold-coated quartz microbalance chips, and the results of dielectrophoretic QCM measurements demonstrated that the greatest responses resulted from template bacilli rebinding.

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女性躍進賞受賞講演

Electrochemical sensors are promising tool for practical sensing device in the wide field of the industry. In this presentation, I introduce two of my researches for the development of electrochemical sensors closely linked to industry. One is the development of endotoxin sensors. Electrochemical Limulus amebocyte lysate (LAL) assay using conventional endotoxin test reagent prepared from horseshoe crab blood represents sensitive and reproducible results which can provide low-cost, compact, easy-to-use practical sensor. The other is the development of Bio-LSIs as part of a national R&D project for integrated microsystems. Bio-LSI has 400 measurement points on a LSI chip with a wide dynamic range from ±1 pA to ±100 nA. Bio-LSI provides a platform for electrochemical real-time imaging as well as simultaneous multiple analyses. Various biosensing have been demonstrated with Bio-LSI including enzyme activity imaging and cell viability assay based on respiration. Progressed versions of Bio-LSI have also developed with cooperative research, including Bio-LSI with microelectrodes made of boron-doped diamond.

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8.

Because of increasing cost of healthcare, much attention has been paid to develop simplified biosensors. As the simplified biosensors, organic field-effect transistors (OFETs) are one of the best candidates. The advantages of OFET-based biosensors are low-cost, easy-fabrication, flexibility and disposability. However, quantitative measurements of proteins by conventional OFETs are difficult because the detection system of the OFET biosensors relies on non-specific adsorption. In this study, we have developed an extended-gate type OFET, and we attempted to detect immunoglobulin G (IgG) using Biotin-Streptavidin interaction. The streptavidin is immobilized on the surface of the extended gate to detect biotinylated IgG. As a consequence, we have observed shifts of threshold voltages of the OFET upon the addition of the proteins in water. This suggests that the biotinylated IgG was captured on the surface of the extended gate. We believe that this result opens up an avenue for development of future OFET biosensors for selective detection of proteins in health-related applications.

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9.

This work aims to develop the miniaturized electrochemical sensor system for practical use. The planar sensor chip equips the Au working electrode, the conductive polymer-reference electrode, and the Au auxiliary electrode. For sensing O157:H7 in sewage, monoclonal antibody of O157:H7 was immobilized onto the carboxy-terminated alkanethiol monolayer by amide coupling reaction. In this work, two types of mixed monolayer were fabricated on the sensor surface. One is mixed antibody-terminated alkanethiol and ethanolamine-terminated alkanethiol monolayer. This immunosensor detected e. coli. in the range of 10^-7 cell ml^-1 to 10^-9 cell ml^-1, and 10^-3 cell ml^-1 to 10^-9 cell ml^-1 by cyclic voltammetry and impedance measurement, respectively. Another type of immunosensing electrode was consisted of antibody-terminated alkanethiol and ferrocene-terminated alkanethiol monolayers. In order to enhance the signal, ferricyanide was added to the phosphate buffered saline solution (pH 7.4). Because a ferrocene played a role of electron-mediator on the electrode, the oxidation current was drastically increased. As e.coli. bonded to antibody and blocked the ferrocenes on the sensor surface, the oxidation of ferrocene was decreased. As a result, e.coli. of a lower concentration than 10^-3 cell ml^-1 could be detected by cyclic voltammetry.

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10.

The chemical imaging sensor is one of the semiconductor-based chemical sensors that can visualize the spatial distribution of chemical species. The chemical imaging sensor is based on the principle of the light-addressable potentiometric sensor (LAPS) that has an electrolyte - insulator - semiconductor (EIS) structure, and uses a scanning light source for mapping the distribution of chemical species. In this paper, we report on the observation of pH distribution around a single colony in detail and propose a small-size scanner head to detect colonies an agar plate .

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11.

Two dimensional refractive index change in the vicinity of an Au sensor chip surface is able to observe by using a surface plasmon resonance (2D-SPR) imager. We have recently applied a 2D-SPR imager with high resolution to develop cell-based biosensing system for drugs without any probe reagents. Response of rat pheochromocytoma(PC12) cells, which were adhered on an Au sensor chip to acetylcholine receptor agonists stimulation was successfully monitored by the reflection intensity change in the individual cell regions on the 2D-SPR imaging.

In this study, response of rat C6 glioma cells to glutamate receptor agonists simulation was observed by using a 2D-SPR imager. C6 cells were stimulated with various concentration of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and kainic acid (KA). We found that the reflection intensity increase of C6 cell regions in 2D-SPR imaging to AMPA or KA injection was dependent on the concentration of the agonist. We further demonstrated that the reflection intensity change of C6 cell regions might be based on intracellular translocation of signal transducing proteins such as PKC to cell membrane.

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12.

We report here the development of highly selective and sensitive detection of β-agonist compounds by using Surface Plasmon Resonance (SPR) immunosensor. Since the β-agonists are illegally used by farmers to increase their profits gain, so the compatible method is urgently required which can measure many samples from food products. For the construction of robust SPR sensor surface, the β-agonist protein conjugates were immobilized onto the sensor surface via functionalized alkanethiol monolayer. Since β-agonists are small molecules, Indirect competitive inhibition method was employed in the detection. It was found that the detectable ranges for ractopamine and salbutamol were 10ppt to 1 ppb and 5 ppt to 500 ppt, respectively. It was also confirmed the 87.1 % and 96.5 % selectivities for ractopamine and salbutamol, repectively. The structures of the sensor surfaces were evaluated by SPR, CV, STM, and XPS.

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13.

We have recently succeeded in two dimensional imaging of pH or oxygen concentration by using fluorescent sensor dye membrane prepared in a Y-shaped mixing flow channel. In this study, glucose oxidase was uniformly immobilized onto oxygen sensor membrane in micro flow channel. We could successfully visualize glucose concentration in micro flow channel. The sensor membrane showed responses only to glucose and not to galactose, fructose or sucrose. Response time was 9s when the flowrate was 0.1ml/min. This imaging sensor chip was applied to visualization of glucose produced in micro flow channel by invertase-catalyzed sucrose hydrolysis reaction. Glucose production could be successfully imaged by using the present method.

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14.

In realizing user-friendly POCT (Point of Care Testing) devices, microfluidic technology is indispensable. In realizing inexpensive disposable devices, electrochemical micropumps are very attractive. Volume change of hydrogen bubbles produced and shrunk on a platinum black electrode can be used to realize bidirectional micropumps. The volume change can be controlled by switching the mixed potential generated with composite electrodes immersed in different electrolyte solutions. We investigated the behavior of devices with three or two flow channels with platinum black, zinc, and Ag/AgCl electrodes. When one of the solutions wetted the zinc electrode, the potential of the composite electrode shifted in the negative direction and hydrogen bubbles were produced. When the other solution wetted the Ag/AgCl electrode, the potential shifted in the positive direction accompanying the shrinkage of the hydrogen bubbles. The obtained results demonstrated a possibility of realizing autonomous bidirectional micropumps for analytical devices.

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15.

An optode-type sensor device which can detect chloride ion was developed. The principle of the sensor is based on quenching of the fluorescence. Acridine Orange (C17H19N3,CAS-No.494-38-2) was used as a chloride ion-responsive fluorescent substance. This material was immobilized on the end face of fiber core with the help of UV curing resin and reflected light intensity at fluorescent wavelength of 530 nm was measured. The sensor device can determine the chloride ion concentration quantitatively. In low concentration range of chloride ion, the sensor output was linearly related to chloride concentration according to Stern-Volmer equation. Therefore, this salinity sensor device could apply to corrosion monitoring of infrastructures such as bridges in the ocean and the coastal areas.

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16.

We propose a novel transducer based on a gapless directional coupler (DC) interferometer. The DC device was designed by the FDTD method. Simulation results provided condition for single-mode waveguiding and suitable connection angle between the waveguide and the coupler. Performance of the device was investigated based on the simulation. A linear relationship was confirmed between changes in signal and refractive index caused as a result of binding of analytes onto the sensing surface. The designed waveguide structure was fabricated by direct electron beam writing on a photoresist (SU-8). SEM images of the waveguide showed its flat surface that minimized a loss of TE0 mode propagation. End-fire coupling between the waveguide and visible light was carried out to investigate the dependence of signal on coupler region length, which agreed well with the simulation results

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17.

For point-of-care applications, a simple cell counter is required to enumerate target cells, such as CD4⁺ T cells or CD8⁺ T cells at HIV/AIDS treatment. Recently we have developed a microcavity array, which can separate leukocytes from whole blood based on differences in the size between leukocytes and other blood cells. We have also developed miniaturized and high-throughput cell analysis system using photosensor array. One-shot imaging of cell groups placed directly on the photosensor array facilitated rapid cell counting. In this study, a simple imaging setup was integrated with the microcavity array to enable single image capture of the entire array and rapid counting of CD4⁺ T cells. We fabricated a wide-field fluorescent imaging system consisting of microcavity array and complementary metal oxide semiconductor sensor. Excitation light was irradiated from the lower side of the microcavity array. Whole blood samples were introduced on the microcavity array and stained with fluorescent labeled antibodies. Fluorescent image of CD4⁺ T cells and CD8⁺ T cells was acquired at one time. Furthermore, the measurement of the ratio of CD4⁺ T cells to CD8⁺ T cells was successfully performed. This system is expected to provide a simple cell analyzer for HIV treatment.

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18.

Dermatophagoides farinae is known as one of the common species of house dust mite producing strong allergen such as Der f1. As preventing and controlling of allergic diseases, the avoidance of exposure to allergens is the first effective way. The aim of this study is to establish a fiber-optic chemifluorescent immunoassay system for detection of Der f1. We used 10- Acetyl- 3,7- dihydroxyphenoxazine (ADHP) as a substrate and horseradish peroxidase (HRP) to produce resorufin that is a soluble and highly fluorescent reaction product with excitation/emission maximal wavelength of 570/585 nm. The measurement system consisted of a green LED excitation system, a photo multiplier tube, a bifurcated optical fiber assembly, filter holders and an optical fiber probe. The immune reagents were incubated in a microtiter well and the well was put in the measurement system. Then the fluorescence signal was recorded. The measurement range for Der f1 was 0.98-250 ng/ml which was equal to ELISA. The system had also high selectivity compared to other airborne allergens.

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19.

Flow-injection determination of zinc(II) ions using alkaline phosphatase immobilized onto carbon fibers was performed. Application of an enzyme-reactor containing a disk type of the immobilized enzymes onto the supports was to a flow-injection system. Performance characteristics of the system were examined. Then, ｍicrodetermination　of zinc(II) ions in nM levels could be realized.

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20.

We proposed a novel ion-sensitive field-effect transistor (ISFET) having a porous-gate structure. Porous structures were formed in n-type InP layers, working as channel layers, grown on p-type (001) substrates. The porous-gate ISFETs could detect the potential changes at the inner pores with a current signal whose value can be controlled by the back gate bias applied to the p-type substrate. Due to the large sensing area and narrow channel at the pore walls, the high sensitivity detection is expected. We demonstrated that the porous ISFET worked as pH-sensors from I-V measurements in 0.1mol/L KCl solution by adding HCl. The sensitivity of the porous-gate ISFETs was 43 times larger than that of the conventional planar ISFET. The results indicate that the porous structures are promising materials as a building block of high-sensitive chemical sensors.

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21.

This paper discusses the chiral discriminative gate effect of molecularly imprinted polymer (MIP) with blended crosslinkers. We grafted L- (or D-) phenylalanine (Phe) imprinted polymer on an indium–tin oxide (ITO) with varied mixing ratio of methylenbeisacrylamide (MBAA) and ethyleneglycoldimethacrylate (EDMA) as crosslinkers. Cyclic voltammetry of ferroccyanide with the grafted ITO electrode was carried out in water solvents and the effect of L- (or D-) Phe on a faradic current of ferrocyanide was evaluated. As the result, the faradic current at the electrode with MIP crosslinked by only MBAA or only EDMA indicated undiscriminative sensitivity to Phe. However that with blended MBAA and EDMA at the ratio of 1:1 or 1:2 indicates chiral-selective sensitivity with the template. Atomic force microscopy indicated that the chiral selective electrode has remarkable roughness. The contact angle of the selective electrode was increased by the template. As a conclusion, the surface roughness and hydrophobization is the essential factor for gate effect in water.

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22.

We have developed several CCD-type ion image sensors with plasticized PVC membrane including an ionophore and/or an ion-exchanger. For previous study, the plasticized PVC membranes were prepared by a cast method; tetrahydrofuran solution including membrane contents was poured onto the sensor and dried. The cast method, however, was hard to prepare a fine membrane with a constant thickness on the image sensor. In this study, an inkjet apparatus was applied to prepare a homogeneous membrane responding to sodium ion. The optimum solvents for the inkjet painting were investigated concerning with viscosity, volatility, and solubility of the membrane contents. The inkjet painting method can finely control the thickness. The sensing pixel covered with the thin membrane indicated the higher potential slope to sodium ion.

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23.

Acidic gases such as HCl and HBr are widely used in industrial fields, including chemical and semiconductor manufacturing processes. Due to their strong toxicity and corrosivity, those gases are required to be monitored at low concentration. Electrochemical gas sensors have advantages in detection of low concentration gases. In this study, we have developed electrochemical gas sensor for acidic gas detection 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 high sensitivity and fast response for HBr and HCl with low interference from coexistence gases such as H₂. The response current for HBr 5 ppm was hardly changed for 300 days.

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24.

Our group has developed all-solid state Na ion-selective electrodes with Na insertion materials as internal mediating layer between substrate and ion selective membrane (PVC). Three Na insertion materials, i.e., Na0.33MnO₂, Na_2/3Fe_1/2Mn_1/2O₂ and Na₂FePO₄F, which are known as candidate materials for positive electrode of Na ion batteries, were employed as the mediating layer. The Pt/-(insertion material)-/PVC electrodes showed much better potential stability than that of the Pt/PVC electrode (i.e., coated wire electrode; CWE). Especially, Pt/Na0.33MnO₂/PVC electrode brought best sodium ion-sensing performance, such as sensitivity, response speed, and potential stability, compared with those of the other electrodes. Furthermore, the electrode impedance was reduced by introducing the insertion materials, leading to superior electrode performance, as the mediating layer successfully makes it possible to stabilize ion/electron transfer at interface between the substrate and PVC membrane.

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特別講演

In 1970s, toxic gas sensor by using a gas permeable electrode was first reported for CO monitoring. By using the gas permeable electrode, a lot of electrochemical gas sensors became available for detection of many kinds of toxic gases in ppm ranges. The sensor has advantage in term of sensitivity, selectivity and power consumption which is suitable in practical fields. We have continued to develop more reliable electrochemical sensors by improving electrode materials, structure of electrode surface and electrolytic solutions. This paper describes our improvement techniques for electrochemical gas sensors.

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25.

Sensing property of diesel particulate matter (PM) using the catalytic combustion-type sensor coated with Pt/TiO₂ and Ag/TiO₂ catalyst was investigated. The sensor coated with Ag/TiO₂ catalyst could detect SOF regardless of the loose/tight contact mode, however, the contact mode that can be detected by the sensor coated with Ag/TiO₂ catalyst changed depending on the temperature. The results suggest that the contact condition between the catalyst and PM greatly influence the response property of the catalytic combustion-type PM sensor. Therefore, it is necessary to study the sensor structure and the drive condition for the PM combustion.

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26.

Sensing properties to various volatile organic compounds (VOCs) of several adsorption/combustion-type micro gas sensors using mesoporous (mp-) alumina loaded with appropriate amounts of noble metals and/or oxides have been examined at an operation with a mode of pulse-driven heating. Among the sensors tested, a Pt (1.0 wt%) and CeO₂ (10 wt%) co-loaded mp-alumina (1.0Pt/10CeO₂-mp-Al₂O₃) sensor showed the largest dynamic response to 1000 ppm ethanol. The sensor showed relatively large dynamic responses to ethyl acetate, o-xylene and acetone, too, while the responses to benzene and toluene were very small. In addition, the co-loading of 10 wt% CeO₂ with 1.0 wt% Pt onto the mp-Al₂O₃ was quite effective in reducing the interference from humidity on the VOC response. The magnitude of dynamic response of the 1.0Pt/10CeO₂-mp-Al₂O₃ sensor was largely dependent on the amount of VOC pre-adsorbed on the mp-Al₂O₃ powder.

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27.

Methane oxidation properties of Pd-based catalysts were investigated for catalytic combustion type gas sensor using MEMS. Support material and promoters for Pd were explored to enhance catalytic property for methane oxidation. From a viewpoint of catalytic activity, Al₂O₃-support was excellent as compared with CeO₂-support, although CeO₂ has property of oxygen supplier. In addition, basic oxides promoters for Pd, MgO and LaMnO₃, didn’t give the enhancement of catalytic activity because PdO was stabilized by basic oxides. However the tendency of catalytic properties was not coincident with the response of MEMS sensor using those catalysts. To develop high sensitive gas sensor using catalytic combustion type MEMS, it is considered that the major factor for catalyst is catalytic property as well as thermal conductivity.

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28.

Silylated graphite oxide thin films were reduced by UV light irradiation using a super high pressure Hg lamp at 95°C. The reduction of silylated graphite oxide was completed within 24h and a new pillared carbon with an interlayer spacing of 0.81 nm was obtained. Pillared carbons with larger interlayer spacings of about 1.13 nm were also obtained from graphite oxide silylated with octyltrichlorosilane and then with 3-aminopropyltriethoxysilane for 1.5 – 6h, when they were reduced by UV light irradiation and then heating at 200°C under vacuum. Selective electrical response during exposure to gaseous vinylene carbonate, acetonitrile, ozone and hydrogen molecules has been achieved by changing the pillar density in the resulting pillared carbon films.

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29.

Poly(N-isopropylacrylamide) (PNIPAM) chains were grafted onto a quartz resonator using surface-initiated atom transfer radical polymerization (SI-ATRP). HCl gas adsorption/desorption properties of resulting PNIPAM brushes were investigated by a quartz crystal microbalance (QCM) technique. Adsorption/desorption properties were affected by the PNIPAM loading (grafting yield). The adsorption capacity increased with an increase in PNIPAM loading, indicating homogeneous adsorption of HCl molecules inside the brushes. The reversibility was insufficient because of the slow adsorption/desorption rate. While the recovery was above 80% when PNIPAM loading was below 10 kHz, the value worsened with increases in the PNIPAM loading. The reversibility was improved with an increase in the measuring temperature, although the adsorption capacity decreased.

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30.

Ultra high-sensitive semiconducting gas sensors for the detection of low-concentration odors have been developed. Its sensing layer consists of core-shell nanostructured powder, which has been prepared by liquid phase deposition (LPD) prosess, depositing SnO₂ or In₂O₃ fine particle film on the surface of TiO₂ or Al₂O₃ particle as core material. The sensor was fabricated by forming a thick layer (several tens of micrometers) of TiO₂-SnO₂ or Al₂O₃-In₂O₃ core-shell nanostructured powder on an alumina substrate with interdigitated Pt electrodes. The fabricated sensors showed extremely high sensitivity, already at a ppb-level of odors like ethanol, VOCs and other harmful gases as compared to conventional semiconducting film sensor. Chromatographic assays of gas mixture have been obtained by our portable gas analyzer, the so called XG-100 in which those type of sensors are employed. Experimental results suggest that our core-shell nanostructured powder and its derived gas sensor can satisfy the demands of detecting odors in various fields.

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31.

Acetone is produced in the blood and expelled through alveoli when body fat is consumed to obtain the energy during fasting or exercising. It is a metabolic product, always present in our breath, and a barometer of fat-burning and hunger level. Easily measuring breath acetone concentration in our daily life to monitor fat-burning can be a strong tool for diet management and is very useful to prevent fatness and life-style related diseases. However, such easy measurement with high accuracy has been difficult because the acetone concentration in breath is quite low and more than 200 gases exist in our breath. Therefore, we have developed a semiconductor gas sensor which has high selectivity to acetone. With this sensor, we have developed a portable device which can measure breath acetone concentration without gas chromatography. The measured results are displayed on a smartphone via wireless signal transfer of Bluetooth®. Breath acetone concentration measured by our prototype and gas chromatograph showed a strong correlation.

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32.

Depletion region formation by the oxygen adsorption on the surface of SnO₂ particles is the most fundamental factor to understand the SnO₂ semiconductor gas sensor. Recently, we proposed two depletion states, which are Regional depletion and Volume depletion, by the theoretical calculation, and Volume depletion behavior was experimentally confirmed. Subsequently two types of oxygen adsorption specie, O- and O₂-, were suggested using experimental results on the relationship between the electric resistance (R) and oxygen partial pressure (PO₂). In this presentation, to examine the transfer on the depletion state experimentally, we investigated the relationships between R and PO₂ in different humidity. According to the relationships in very low PO₂ region, tendency of Regional depletion behavior was observed, and it was clearly corelated with humidity. The obtained results are important for designing the sensor materials.

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33.

In the study, we aimed to confirm the effect of Pd on the SnO₂ sensor by investigating the oxygen adsorption behavior and sensing properties to H₂ under different humid condition. Based on theoretical model and formulas reported ptreviously, it was found that oxygen mainly adsorbed as O₂- for Pd-loaded SnO₂ in high humid atmosphere. Additionally, the sensor response was enhanced by Pd in wet atmosphere, maybe due to the chemical effect of Pd which contributes to the reaction of H₂ with OH- and O₂- to form H₂O.

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34.

Sensing properties to H₂ and NO₂ of a SnO₂ semiconductor gas sensor were investigated at 30ºC in air with and without different UV-light irradiation power (wavelength: 365 nm). The resistance drastically decreased by the UV-light irradiation, and the resistance increase upon exposure to O₂ in dry N₂ was much highlighted with the UV-right irradiation.　Less pronounced improvement of H₂-sensing properties of the sensor was induced by the UV-light irradiation, while the magnitude of NO₂ response and the recovery speed in dry air were largely improved by the UV-light irradiation at 30ºC. In addition, the UV-light irradiation drastically reduced the interference from humidity on the magnitude of NO₂ response.

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35.

Gas sensors are important devices because they are used in various systems such as security, in-car device, environment monitoring and so on and important devices and it is expected that they will be mounted in mobile phones or smartphones. Improvement of portability requires miniaturization, reduction of power consumption and sophistication of sensor devices. Miniaturization and integration of sensors are essential for realization of them. Integration of sensors is important from the view point of improvement of redundancy and reliability. The technology for miniaturization and integration of sensors must have compatibility with photolithography which is known as the typical top-down process and it requires development of methods and materials to form homogeneous nanostructures. Therefore, in this study, we developed a hybrid process between photolithography and anodization, which can form a self-organized homogeneous nanohole array and formed titanium oxide (TiO₂) nanotube film at a micro region in a titanium micro wire to fabricate a hydrogen micro gas sensor.

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36.

Yamazoe and Shimanoe have developed a well-organized theory of the response of a semiconductor gas-sensor 1,2), where the response based on electronic structure of the semiconductor was discussed in consistency with the chemical equilibrium for the surface reaction. While their theory is based on the approximation of the abrupt model, they also investigated the abrupt model with modification involving the effect of electrons injected into the electron-depletion region. In this study, we discuss the gas response based on the precise solution of Poisson’s equation for the band bending at the surface, where the results are compared with those obtained by the abrupt model and modified model.

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37.

SmFeO₃ semiconductive sensor was applied for detecting 17 kinds of VOCs, which have different chemical structures (alcohols, ketones, esters, acids and aromatics). The sensor responded well to the VOCs in 0.5~10ppm and 400oC was the optimal operation temperature. In order to characterize the sensor responses, we performed the curve fitting of the sensor response data based on a following equation, Rvoc/Rair=1+Cvoc1/m. Of the VOCs, polar compounds tended to have large  and m-values, suggesting that such the compounds are expected to have large response even at extremely low concentration. In fact, the expectation values of Rvoc/Rair for 0.01 and 0.001ppm ethanol, MEK and n-butanol at 400oC were around 13 and 20, respectively. The -value was dependent not only on functional groups but also molecular weights of the VOC molecules.

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38.

Sensing performance of SmFeO₃ is related to its Sm-enriched surface. In this study, Sm₂O₃ was impregnated onto SmFeO₃ surface to achieve a further enrichment in Sm. The Sm-enrichment was effective to enhance the sensitivity to toluene. According to the XPS measurement, the concentration of adsorbed oxygen increased with increasing the amount of the Sm₂O₃ additive. This oxygen-enriched surface would be effective to enhance the VOC reactivity. Furthermore, it was found that the amount of toluene adsorption increased with increasing the amount of the Sm₂O₃ additive or the adsorbed oxygen. We tentatively assigned that the surface Sm-O acted as toluene adsorption site

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39.

In this study, we focused on the preparation of WO₃ particles with different morphology and their NO₂-sensing properties. Cubic-shaped (C-) and hexagonal-disc-shaped (H-) WO₃ particles were prepared by precipitation and hydrothermal synthesis. WO₃ sensors were fabricated and tested on responses to dilute NO₂ (20 ppb to 1 ppm) to investigate how NO₂ sensing properties are related to the morphology or crystal structure of the sensing materials. The temperature dependence of the sensor response showed that the optimum operating temperature of the C- and H-WO₃ sensors was 200 °C. The C-WO₃ thin-film sensor showed the highest sensor response of 160 to 20 ppb NO₂, and fast sensor response of 2.4 and 0.8 min for the 90 % response and recovery times, respectively. The temperature dependence of the H-WO₃ sensor response is smaller than that of the C-WO₃ one and showed high response in a relatively low temperature range of 60-120 °C. However, the recovery of the H-WO₃ sensor was much slower as 1.8 min for the 90 % recovery time. The crystal structure of C- and H-WO₃ samples was investigated by solid-state 1H MAS (magic angle spinning) NMR measurements. In the spectrum of as-synthesized H-WO₃ particles, impurities from the precursor material were confirmed, which might also impact on its sensing properties.

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40.

In this study, we focused on the composite effects of p-type MgO and n-type MgFe₂O₄ on H₂S detection. The mixture state of these oxides was fixed by coprecipitation conditions: mixture ratio of iron source to magnesium source, and pH control of precursor solution by dropping of an alkaline solution. The composite mixture of MgO, Fe₂O₃ and MgFe₂O₄ was obtained by adjusting the mixing ratio of Fe to Mg. The resistance in air was monotonically increasing with increasing the quantity of MgO in the matrix of MgFe₂O₄. In contrast, the resistance in air was decreased with the increase of Fe₂O₃ in the quantity. The sensing properties of these composites to 3 ppm H₂S were evaluated as a sensor response (S), defined as the ratio of the resistance in air (Ra) to that in gas mixture of H₂S and air (Rg). The sensor response was depended on the composite state of MgFe₂O₄ and MgO because the absorbed amount of H₂S on the composite was increased by the formation of p-n junction. In contrast, the sensor response was low despite of the high resistance in air when the excess MgO existed in the matrix of MgFe₂O₄, suggesting that the excess MgO plays a role of insulator in the electron transfer between semiconductor composite of MgO-MgFe₂O₄ and Pt interdigitated micro electrode.

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41.

A potentiometric gas sensor using yttria-stabilized zirconia (YSZ) as a solid electrolyte and ZnO(+ 84 wt.% Ta₂O₅) as a sensing electrode (SE) was developed and demonstrated the capability to detect H₂ sensitively and selectively. The H₂ sensitivity was found to be stabilized at high level after the 40-day stabilization (aging) process at 500oC. In this study, efforts to reduce the long stabilization period were initially conducted by changing the sintering temperature and prolong the sintering time of the sensor. Unfortunately, none of these examined treatments succeeded in accelerating the stabilization process. However, when the sensor was subjected to the exposure of 400 ppm H₂ (diluted with N₂) during the aging, an acceleration in the stabilization process was observed. Interestingly, more frequent exposure of 400 ppm H₂ did not work to accelerate the stabilization of the H₂ sensitivity. Therefore, a less 400 ppm H₂ treatment is the appropriate formula to achieve a shorter stabilization period. The sensitive and selective responses toward H₂ that were observed for the stabilized sensor with a shorter stabilization period, indicating that the sensing characteristics toward H₂ were unaffected even by the H₂ treatment.

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42.

Many oxides were examined here for selection of an excellent sensing electrode (SE) material of YSZ-based oxygen sensors. First, the emf responses of the obtained sensors toward various gases (100 ppm each) were measured. As a result, among the oxides tested, some specific perovskite oxide was found to give insensitive characteristic to any reducing/oxidizing gases which usually exist in automotive exhausts. In addition, the obtained sensor attached with this perovskite-oxide SE was confirmed to be able to operate as a good oxygen sensor in the concentration range from 0.05 to 21 vol.% at 600℃. In this case, the number of electron (n) for the electrochemical reaction of oxygen was about 4.2 before and after a two-week operation, suggesting a good stability of this sensor. Furthermore, the present sensor was found to work as a lambda sensor; the emf value of the sensor was drastically changed around 1.0 in lambda value at 600℃. Therefore, it is concluded that the selected perovskite oxide is considered to be as one of attractive alternatives to a conventional Pt-SE of YSZ-based oxygen sensor.

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43.

Pt pastes are used for heater, reaction electrodes and leads of the planar ZrO₂ oxygen sensor. Manufacturing cost of the sensor highly depends on the Pt pastes. Therefore reduction of Pt usage is compelling needs and can be realized by lowering the resistance. Ceramic powder, which is a constituent of the Pt paste, suppresses the shrinkage of the Pt paste to match the ceramic green sheet during a firing process. In this study, utilization of Pt core and oxide shell powder is examined as alternative material of the ceramic powder. Usage of the conductive core shell powder decreases resistance of the heater and lead. 30% reduction of Pt is realized with the core shell powder paste as a result.

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44.

Y₂O₃-Stabilized-ZrO₂ (YSZ) oxygen sensor operating at lower temperature was investigated. Commercially available oxygen sensors typically consist of YSZ bulk electrolyte with Pt electrodes, which are operated above 600oC. Below this temperature it is difficult to measure an electromotive force (EMF) accurately because of the lower mobility of oxide ions in the electrolyte and lower efficiency of oxygen exchange reaction at the gas-electrode-electrolyte interface. It was reported that (La,Sr)(Co,Ni)O₃ (LSCN) bulk electrode had good catalytic performance even at 200oC [1]. Although LSCN is considered as one of the candidate materials of the electrode for the low-temperature operation, electrical and catalytic properties of the LSCN thin-film have not been clarified yet. In this study, LSCN thin-film was deposited on (100) YSZ single-crystal substrate by PLD method and catalytic performance of the film at the lower temperatures was measured with changing the microstructure, the conductivity and the crystallinity. YSZ oxygen sensor with LSCN nanoscale insular electrode deposited for 1min at 600oC under Pt collector electrode can operate even at 200oC with relatively a short response time because of large reaction area.

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