Vol. 32, Supplement A (2016)

1.

We have found that electrochemical response derived from ferrocene (Fc) conjugated on DNA aptamer could be improved by a simple heat treatment. Although DNA aptamers are usually immobilized on gold electrode using gold-sulfur interaction, they often generate undesired aggregates and adsorb on the electrode surface non-specifically during immobilization step. These problems have inhibited DNA aptamer from capturing target molecules and Fc from coming close to the electrode surface. Effects of heat treatment after the immobilization on electrochemical response were investigated by typical sweep and pulse techniques. Cocaine was chosen as a target molecule because of its affordable molecular size. The temperature dependence of the heat treatment was also investigated.

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2.

We have developed an immunosensor that allows repetitive measurement of dust mite allergens (Der f 1) by exploiting a surface acoustic wave (SAW) device and highly stable protein (Orla protein). A gold coated delay line of the SAW device (sensing part) is modified with a self-assembled monolayer of a mixture of Orla protein and polyethylene glycol thiol. Capture antibodies are bound to protein G fused to Orla protein, followed by bindings of Der f 1 and detection antibodies. Due to high resistance of Orla protein to pH change, the sensor surface can be regenerated by changing pH repeatedly without substantial degradation. As a result, an experiment performing 10 successive sandwich assay of Der f 1 showed high reproducibility (C.V.=5.6%). The limit of detection of the sensor was 6.1 ng/mL which encompasses the standard set by the World Health Organization (WHO). Selectivity of the sensor was also evaluated with common allergens, and output was not observed from samples without Der f 1 but obtained from all of samples containing Der f 1. These properties allow us to anticipate that the SAW immunosensor can be applied for semi-continuous measurement of mite allergen in indoor environment.

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3.

Electrochemical behavior of leucodopaminechrome and its synthetic pathway from dopamine on carbon nanotube electrode is reported. Regardless of various carbon nanotubes’ parameters such as diameter (single- and multi-walled), length, and chirality, coupled redox pairs due to leucodopaminechrome originated from dopamine were manifest by cyclicvoltammetry. This attributes that the particular environmental of carbon nanotube surface maintained the reversibility of two redox reactions, dopamine/dopaminequinone (+0.22/+0.11 V vs. Ag/AgCl) and leucodopaminechrome /dopaminechrome (-0.12/-0.34 V vs. Ag/AgCl). The range of pH 7.4-7.8 maintained the best balance of the reversibility by differential pulse voltammetry in which the peak current at -0.12 V due to LDAC oxidation is the largest. At more than pH 8.0, the peaks due at +0.22 V to dopamine oxidation became larger while that due to leucodopaminechrome oxidation became smaller because the intramolecular cyclization rate of amine group of dopaminequninone increase, then, the reversibility of two redox pairs is broken. Quantitative and selective detection of dopamine with the signal due to leucodopaminechrome oxidation is possible. The linear range was 10-360 M and detection limit was 0.08 M.

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4.

　A paper-based immunochromatographic assay devices based on colorimetric method has been widely used for a diagnostic kits such as pregnancy test and flu test. Simultaneous multi-analyte detection device using colorimetric method was also reported. However, it is difficult to determine an analyte concentration with high quantitative accuracy by colorimetric method. Gold nanoparticle-labeled antibodies are often used for the immunochromatographic assay. In the present study, we investigated change in solution conductivity due to the aggregation of gold nanoparticles in a chromatography paper by electrochemical impedance. It would lead to the development of a paper-based impedimetric sensor with high quantitative accuracy.

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5.

The microneedle (MN) array, a two-dimensional array of submillimeter-long needles that penetrates skin, has attracted much attention, as they have potential as a minimally invasive method to bypass a skin barrier and interface with the inside of a human body. We have fabricated polymer MN arrays with continuous micropores by polymerizing an acrylate monomer in the presence of a porogen within a soft poly(dimethylsiloxane) mold. Scanning electron microscopy of the fabricated MNs revealed that the MNs have interconnected pores with a typical diameter of 1 um on the surface and inside of MNs. The MN arrays penetrated the skin with >80% efficiency when the force of 1 N/needle was applied, which was examined by trypan blue staining. Water absorption speed of the MN arrays was tested by putting the MN array on an agarose gel containing colored water. It showed water can go through the MNs up to the base by capillary action within 5 min, which indicates that the pores are continuous through the MN. Efficient skin penetration and fast water absorption of the developed MNs will enable continuous monitoring of interstitial fluid in a minimally invasive manner.

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6.

We have been developing electrochemical biosensors based on nanocarbon films formed by unbalanced magnetron (UBM) sputtering techniques. The film shows wide potential window because of hybrid structure of sp² and sp³ bonds and low capacitive current due to very flat surface. We previously reported electrochemically stable fluorinated nanocarbon (F-nanocarbon) film by CF₄ plasma treatment and applied for quantitative measurements of hydrophobic antioxidants (α-tocopherol) with maintaining the suppression for the responses of hydrophilic antioxidants (ascorbic acid). We also applied F-nanocarbon film electrode to construct a current amplification system in combination hydrophobic ferrocene mediators and hydrophilic Fe²⁺ ions as a reductant. The F-nanocarbon film exhibited typical electrochemical reaction of ferrocene based mediator, whereas strongly suppressed the electrochemical oxidation of Fe²⁺ ions. This selectivity provided current amplification of ferrocene mediators with Fe²⁺ ions solely by using the F-nanocarbon film electrode without interference from direct oxidation current of Fe²⁺ ions. The above current amplification system was applied for electrochemical biosensor of lipopolysaccharide.

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特別講演

Glassy carbon (GC) and carbon felt (CF) were electrooxidized in ammonium carbamate aqueous solutions, and we have examined the electroreduction of these electro-oxidized GC and CF in sulfuric acid electrolyte. These multielectrolyzed carbon materials have specific elctrocatalytic activities such as hydrogen oxidation, oxygen reduction, oxalic acid　oxidation, hydrogen evolution, and have been utilized as detection elements of chemical sensors. Moreover, these have also catalytic activities for hydrogenase or oxidase reactions. Platinum is electrodeposited at the surfaces of the multielectrolyzed GCs by the electroreduction of Pt ion dissoluted from Pt counter electrode, and this electrodeposited Pt was removed by ultrasonication, resulting in remain of 1.5% Pt which must be in collaboration with the N-containing functional groups creating novel catalytic abilities. This Pt deposited multi-electrolyzed electrode gave very stable hydrogen evolution current similar to that obtained by Pt disk electrode in the same size.

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清山賞受賞講演1

We have studied several sensing methods by electrochemical, electrogenerated chemiluminescence (ECL) and surface plasmon resonance techniques utilizing surface sciences for biomolecular determination. For examples, we reported an ECL based enzyme linked immunosorbent assay (ELISA) using products from the enzymatic reaction of a labeled antibody as the ECL coreactant. This is advantageous for the direct labeling of coreactants to an antibody since we can greatly enhance the signal by enzymatic amplification. As a result, the combination of ELISA and ECL detection has the advantage of achieving a high signal-to-noise ratio and this allowed us to measure trace level tumor necrosis factor-α and DNA methylation. We also developed the sequence-selective ELISA-like discrimination of the DNA methylation status. This was achieved by bulge-specific antibody recognition with respect to methylcytosine employing the free rotation of methylcytosine in a DNA bulge region. The proposed assay allows us to determine whether or not the target cytosine is methylated with a single base level without being affected by the cytosine methylation status in the non-target region.

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7.

We have developed a novel electrochemical bacterial sensing technique using a tetrazolium salt, MTT, which is reduced by living bacteria to produce an insoluble formazan compound. Application of a 5-µL suspension of E. coli and MTT, which had been incubated for 1 h, on an ITO electrode gave two-pairs of well-defined voltammetric peaks, which resulted from the surface-confined event of the formazan. The peaks were only found after the incubation with living E. coli, and the anodic peak at +0.07 V vs. Ag|AgCl was used for the determination of the cell density. The technique developed here allowed us to determine the E. coli cells down to ca. 5x102 cell mL-1, which was 10-100 fold more sensitive than the values reported for the colorimetric techniques using tetrazolium salts.

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8.

Mental stress is closely related to the function of the immune system. To evaluate the degree of the stress rapidly, we measured changes in the respiratory activity of E. coli using a microfabricated Clark-type oxygen electrode coupled with a microfluidic channel. The respiratory activity of E. coli is directly related to the phagocytic activity of neutrophils. To improve the usability of the device, the application of freeze-dried E. coli was tried in this study. The current changed linearly up to 1.0×10⁷ CFU/mL E. coli concentration. Neutrophils were separated from whole blood obtained from a normal mouse and a stressed mouse that was restricted and immersed in warm water for 2 hours. A clear difference was observed between the two cases. The results demonstrated that our device with freeze-dried E. coli can be used to evaluate the degree of mental stress.

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9.

Detection and discrimination of contaminated microorganisms in the samples of interest are crucial in a wide range of industries including foods, cosmetics and pharmacy manufacturing. Identification of pathogenic microorganisms is also of great importance in clinical diagnosis. Traditionally, colony formation and its morphological analysis by bare eyes (e.g., size, shape and color) have been employed for this purpose. However such conventional method is time consuming, labor intensive and less reproducible. In this study, we developed the lens-less imaging systems to analyze microcolonies (diameter of 10~500 μm). This system is composed of a complementary metal oxide semiconductor (CMOS) sensor and medium agar plate that is directly placed on the sensor. Microorganisms can grow on the medium agar plate above the sensor, and the cell growth can be observed as the expansion of the microcolonies. This lens-less imaging system has the advantage of wide field of view, enabling simultaneous tracking of multiple microcolonies. Discrimination of five different microorganisms (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella enterica, and Candida albicans) was demonstrated by statistical image analysis. Since the proposed system could take a number of potential advantages of rapid and high-throughput testing, inexpensive instruments, high reproducibility, and ease of automation, it would be a promising method for identification of the contaminated microorganisms in a variety of applications.

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10.

Single cell can be isolated using microfluidic disc for single cell isolation and the isolated cells can be distinguished by PCR of their specific gene. The purpose of this study is establishment of discrimination method between archaea and bacteria on microfluidic disc for single cell isolation. Two different forward primers and TaqMan probes targeting 16S rRNA gene were used to discriminate Metallosphaera sedula TH-2（archaea）and Escherichia coli B (bacteria) as model organisms for the discrimination. To detect archaea and bacteria, FAM probe and TAMRA probe was employed respectively. Specificity of these primers and TaqMan probes was confirmed by real-time PCR. Cell suspension (3×10⁵ cells/µL M. sedula and 3×10⁵ cells/µL E. coli) and PCR reagent was mixed, and the mixture was injected into the microfluidic disc. Cell lysis by heat treatment (95°C, 5min) and PCR was performed on the disc. Before and after PCR, fluorescence of FAM and TAMRA of each chamber was measured by a fluorescent microscope on the device. As a result, we confirmed detection of archea and bacteria on the disc after single cell isolation. The limit of detection was 950 cells/µL M. sedula and 3,000 cells/µL of E. coli on the device.

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11.

Field effect transistor (FET) biosensors detect the change in interfacial potential caused by specific bindings between probe molecules immobilized on the surface of FET gate insulator and target molecules, such as proteins and DNA, for example, in electrolytes. However, by using FET biosensors, it is difficult to detect the proteins having a small net charge. In our previous study, the response of FET biosensors with antigen-binding fragment (Fab) as a probe (Fab-immobilized FET) to the target protein having a small negative charge was amplified when the target protein was pretreated with an anionic surfactant, sodium dodecyl sulfate (SDS). In this study, the FET responses obtained for the target protein treated with anionic, cationic, and nonionic surfactants were compared to verify the effect of electric charge derived from surfactant on the signal amplification. In addition, the attachment of surfactant to protein was examined by fluorescence spectroscopy.

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12.

A real-time heparin sensor is required to optimize dosage of heparin for extracorporeal circulation and its antidote protamine. Then, we are trying to develop a heparin sensor using a molecularly imprinted polymer (MIP). In the present work, we studied the method to stabilize measurement of heparin concentration in whole blood by using the MIP-grafted electrode. An initiator of radical polymerization was introduced on an indium-tin oxide (ITO) electrode. Heparin sodium, methacryloxethyltrimethoxysilane, and acrylamide were dissolved in water. Methylenebisacrylamide was dissolved in dimethylformamide. Mixture of the both of the solutions was introduced into the gap between the surfaces of quartz crystal plates and the treated ITO electrode. Ultraviolet was irradiated to the surface of the ITO to graft copolymer of the monomers. The ITO was washed with aqueous solution of 1 M sodium chloride to remove the template and to obtain the MIP-grafted electrode. Cyclic voltammetry was performed with the MIP-grafted electrode in physiological saline or bovine whole blood including 0-8 unit/mL heparin and 5 mM ferrocyanide as a redox marker. The heparin-sensitivity in the blood with the washed electrode was 50% of that in the saline. Then the whole blood was filtrated with the dialyzer module and the most of the plasma protein was removed. The heparin and the ferrocyanide were dissolved in the filtrate and the fluid was used for the cyclic voltammetry. The heparin-sensitivity of the current in the filtrate was almost same as that in physiological saline. Then the removal of plasma protein from the blood sample is effective for reliable sensing of heparin using the MIP-grafted electrode,

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13.

Aiming for on-site measurement of the activity of lymphocytes in response to drugs, an optofluidic device with integrated optical components and microfluidic structure was used for the determination of interleukin-2 (IL-2). Lenses and mirrors were formed with poly(dimethylsiloxane) (PDMS) using the difference in the refractive indexes between PDMS and air. The flow channel structure had an air bypass to enable selective immobilization of capture antibodies only in the measuring chamber and avoid denaturation of proteins while exchanging solutions there. To immobilize capture antibodies, in-situ functionalization was carried out to increase sensitivity. Enzyme-linked immunosorvent assay (ELISA) was conducted on the chip. Clear concentration dependence was confirmed for IL-2 concentrations ranging from 50 to 1000 pg/mL, which is adequate for the determination of cytokines secreted from lymphocytes. Response of lymphocytes obtained from whole human blood was measured using the device.

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14.

A low invasive type glucose sensor, which has sensing region at the tip of a fine pointed electrode, was developed for continuous glucose monitoring. Electrodeposition of glucose oxidase in the presence of surfactant, Triton X-100, was performed for high-density enzyme immobilization, and was followed by the electropolymerization of o-phenylene- diamine for the formation of functional entrapping and permselective polymer membrane. Ag/AgCl film was coated on the surface of PEEK tubing as reference electrode. The prepared electrode showed the sensitivity of 2.55 mA/cm² mM with high linearity of 0.9986, within the glucose concentration range up to 21 mM. The detection limit (S/N = 3) was determined to be 0.11 mM. The glucose sensor properties were evaluated in phosphate buffer solution and in vivo monitoring by the implantation of the sensors in rabbit, while conventional needle-type sensors as a reference were used. The results showed that change in output current of the proposed sensor fluctuated similar with one in output current of the conventional needle-type sensors, which was also in similar accordance with actual blood sugar level measured by commercially glucose meter.

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15.

Alzheimer's disease ( AD ) is one of the type of dementia. The neuropathological diagnosis of AD is decided upon the detection of amyloid plaques which made by insoluble amyloid. It is known that the amyloid is produced by β-secretase and γ-secretase which catalyze the amyloid precursor peptide. The -Secretase is one of a key enzyme for development of therapeutic agent to AD because the enzyme activity is specifically high in AD patient. All the conventional β-secretase inhibitors are substrate analogs, it means that those inhibitors are competitive and reversible inhibitor. Therefore, a non competitive enzyme inhibitor of β-secretase will be able to be a novel reagent as an anti-AD. In previous study, we report the development of new system to evaluate non-competitive inhibitor against β-secretase by using flow injection analysis (FIA) in combination with immobilized β-secretase. In the system, we use commercially available FRET (Fluorescence Resonance Energy Transfer) substrate constructed from fluorochromes and the recognition sequence linker for β-secretase. The FRET substrate is expensive and is not suitable for in vivo analysis of β-secretase. In this study, we developed fusion protein which is made from ECFP, EYFP, and those linker including β-secretase recognition sequence as a novel FRET substrate and evaluate the properties. This protein has advantage not only in cost effective screening for β-secretase inhibitor but in in vivo assay for β-secretase activity.

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16.

Uricase (UOx) and horseradish peroxidase (HRP) were physically adsorbed onto porous carbon felt (CF), which is a microelectrode ensemble of micro carbon fibers (ca. 7 μm in diameter) possessing a random three-dimensional structure. HRP and thionine (Th) were firstly adsorbed onto the CF, and then, the UOx was further adsorbed onto the HRP/Th-CF. The resulting UOx, HRP and Th-adsorbed-CF (UOx/HRP/Th-CF) was successfully used as a flow-through detector for amperometric determination of uric acid. Enzyme-adsorption conditions and operational conditions were optimized. The developed FIA biosensor showed the sensitivity (0.59 μA/mM), the limit of detection (0.05 μM, S/N =3), and linear range (0.3 ～ 10　μM). The relative standard deviation for 50 consecutive injections of 10 μM uric acid was 1.77 %. The developed　biosensor was applied for the determination of uric acid in urine and serum, and the analytical results obtained by the sensor was fairly good agreement with those by the conventional spectrophotometry.

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17.

Modifications of preparation methods of immobilized alkaline phosphatase onto carbon fibers chemically treated were investigated. Three pieces of the immobilized preparations were applied to a flow-injection determination of zinc(II) ions. The modifications of the carbon fibers and performance characteristics of the flow system were reported.

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18.

An amperometric biosensor based on glassy carbon electrode modified with long-length multi-walled carbon nanotubes (MWCNTs) and enzyme nicotinamide adenine dinucleotide dependent glucose dehydrogenase (GDH) is presented. We demonstrate the effectiveness of MWCNT length toward the amperometric response of enzyme biosensor. The long-length of MWCNT is 200 m (average), whereas normal-length of MWCNT as a comparison is 1 m (average). The response of long length MWCNT-GDH electrode was 2 times more sensitive than that of normal-length MWCNT-GDH electrode. Electrochemical impedance spectroscopy measurements suggested that the long-length MWCNT-GDH electrode formed a better electron transfer network than the normal-length one.

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Surface Plasmon Resonance (SPR) biosensor has been developed in our group. For detection of small analyte, we study the indirect competitive inhibition immunoassay and the signal amplification using Localized SPR phenomenon (LSPR). It was noticed that the high sensitivity could not be achieved by only the amplified signal change but also the affinity constant between the target molecule and the sensor surface. However, the kinetics study of indirect competitive inhibition is very complicated. Further, in order to provide the LSPR effect, the Au nanoparticle (NP) is used for labeling to antibody (Ab). As the size of reactant, Au NP modified Ab, becomes a large, the mobility is also changed. Thus, the affinity constant would be changed due to its mobility. In this study, we focus on the labeling effect on the kinetic factor. Primary and secondary Abs were labeled with 40 nm Au NP, because total size of approximately 60 nm shows the highest signal amplification. It was found that the sensitivity became a high because the affinity constant became a low by Au NP labeling in the immunoreaction of primary Ab. In contrast, the sensitivity became a high, because the affinity constant became a high in the secondary Ab immunoreaction.

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We here describe the development of immunosensing systems with chemically-amplified responses and those based on the dielectrophoretic manipulation of microparticles. Chemical amplification that involves a reaction sequence to generate a relatively large amount of product near the transducer surface is a useful way to enhance the sensor response effectively. The dielectric manipulation of microparticles provides simple and rapid immunoassay protocols. Highly-sensitive, rapid and simple imunosensing methods are suitable for the purpose of point-of-care testing of biomarkers.

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33.

Acetone has been attracting attention as a human biogas, and it can be detected in the breath of diabetic patients. Therefore, a method to easily measure trace amounts of acetone is important. Focusing on 2,4-dinitrophenylhidrazine(DNPH) which was used in a detection tube, a sensor element was made by impregnating the reagent into a porous glass with large surface area. We tried to detect acetone using the sensor element. Acetone-DNPH is a produced by the reaction between acetone and DNPH. It shows a UV-Vis spectrum similar to DNPH and its molar absorbance coefficient is approximately 1.86 times of DNPH. Our research showed that the wavelength of maximum absorption of acetone-DNPH was found to be shifted to longer wavelength of 14 nm than that of DNPH. Considering these things we tried to detect acetone by spectral analyses of the sensor element before and after exposure to acetone, and we could detect acetone from sub ppm to 10ppm with 1 hour exposure.

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34.

A bio-fluorometric imaging system (Sniff-cam) exploiting an enzymatic reaction was developed for measurement of gaseous acetaldehyde (AA) in exhaled breath. This system consisted of a highly sensitive camera, an ultraviolet-light emitting diode (UV-LED) array sheet and an alcohol dehydrogenase (ADH) immobilized mesh. Reduced Nicotinamide adenine dinucleotide (NADH) is consumed by the enzymatic reduction of AA with ADH, and its concentration is inverse-proportional to that of gaseous AA. In this system, the concentration of gaseous AA is quantitatively visualized with fluorescence intensities emitted from NADH by UV photo-excitation. The detection limit of 100 ppb with the high-selectivity for AA vapor was demonstrated in the sniff-cam. Finally, the Sniff-cam was applied to measure gaseous AA in exhaled breath after intake of an alcohol beverage, and a fluctuation of AA concentration with time was observed as alcohol metabolism.

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35.

An acetone bio-sniffer (biochemical gas sensor) was constructed and used for measuring acetone concentration in exhaled air. The bio-sniffer was composed by a flow-cell with a secondary alcohol dehydrogenase (S-ADH) immobilized membrane, an optical fiber and a UV-LED excitation light source. NADH would be consumed by the S-ADH enzymatic reduction of acetone and the consumption volume is proportional to the concentration of acetone. Phosphate buffer, which contained NADH, was circulated into the flow-cell for supplying co-enzyme and removing the excessive substrates and products. The decrease of the fluorescence intensity emitted from NADH is detected by the photo multiplier. We also demonstrated that the alter value of fluorescence intensity was correlated with acetone concentration from 20 to 5000 ppb. This calibration range includes the concentration of acetone in the breath of healthy people (200 – 900 ppb) and those (>900 ppb) suffering from disorders of carbohydrate metabolism. Finally, the acetone bio-sniffer was applied to measure the exhaled acetone that produced by lipid metabolism inducing from an exercise tolerance test. The concentration of acetone in breath was shown to significantly increase with exercise. This highly sensitivity acetone bio-sniffer for human breath is expected to apply for the clinical diagnosis.

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特別講演

In recent years, real driving emissions from vehicles are paid much attention from the point of view of the environmental protection. Nevertheless, vehicle emissions on the roads have not been evaluated sufficiently yet, from lack of authorized measuring method and/or instrument. Recently, portable emissions measurement systems, which typically consist of gas analyzers for CO/CO2/NOx/THC, exhaust gas flow meter, and various sensors to monitor running conditions of test vehicle, have been developed for such a purpose. This paper describes the configuration of a portable emissions measurement system (PEMS). Test results of the real-world measurements are also shown.

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36.

To understand the state of the adsorbed oxygen on the surface of the SnO₂ at the time of ultra-short pulse drive, we examined the relations between partial pressure of oxygen and sensor resistance compared with continuous state considering only the overall reaction equilibrium. We found that in the case of ultra-short pulse heating, the result is different from continuous heating. Therefore, under the ultra-short pulse heating condition, adsorbed oxygen species is different from that under the continuous heating, or relation obtained by analyzing the equilibrium of the overall reaction is not necessarily satisfied under the condition of ultra-short pulse heating.

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37.

Characterization for structure and thermal stability of Sn_1-xPtxO₂ thin film with solid state structure produced by sputter deposition was investigated, which showed high selectivity and long life time as gas sensor. XRD (X-ray diffraction) and TEM (Transmission Electron Microscope) showed that Sn_1-xPtxO₂ has a nano-columnar structure aggregated by fine particle having order of a few nm. Moreover we have demonstrated by XRD and XAFS (X-ray Absorption Fine Structure) that Sn_1-xPtxO₂ was maintained as rutile structure even heating of 600 deg C higher than sensor temperature.

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38.

We have investigated monitoring of lung cancer-related volatile organic compounds (VOCs) (nonanal, n-decane, and acetoin) and sugar diabetes-related VOCs (acetone and methyl i-butyl ketone) in simulated room air with humidity. We have used 31 kinds of VOCs as simulated contaminated room air, as this has been proposed to resemble an indoor air-like gas. We have collected sensor signals from a sensor array comprising four commercially available sensors (Figaro TGS 2600, 2602, 2610, and 2620), our laboratory-developed tin oxide-type sensors (Pt, Pd, and Au loaded SnO₂ (Pt,Pd,Au/SnO₂)) and another kinds of sensors. The signals from sensors array have been analyzed using principal component analysis (PCA).

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39.

Semiconductor gas sensor is heated by the heater at the time of gas detection. By reacting with the high concentration gas, it causes the sensor element to reach a very high temperature. For this reason, high-concentration gas adversely affects the sensitivity of the semiconductor sensor. Therefore, we have developed the following sensor driving method. 1) If the gas concentration rapidly rises, it will turn off the heater. 2) The sensor can continue to detect gas at high concentration by switching to short time heating. 3) If gas concentration returns to low continuous heating will resume. This experimental result shows that the influence of high-concentration gas can be prevented.

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40.

We have developed a method to confirm the transition of flammable gas from air by the use of a MEMS (Micro Electro Mechanical Systems) semiconductor gas sensor. When gas meters and pipes used for flammable gas, such as city gas or LPG, are set up　or changed, internal air must be substituted to flammable gas. Using a conventional pumping-type gas detectors, air was checked to be replaced by flammable gas, however, the pumping-type gas detector took time to introduce sampling gas to the sensor and to emit that gas. By installing the MEMS semiconductor gas sensor in a pipe, we can catch the transition of the flammable gas more quickly and safety than a conventional method.

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41.

The catalytic combustion behavior of ethanol or toluene over the mp-Al₂O₃ co-loaded with 10 wt% MO (CeO₂ or Bi₂O₃) and 1.0 wt% Pt (1Pt/10MO-mp-Al₂O₃) and temperature-　programmed desorption (TPD) characteristics of ethanol or toluene adsorbed on them have been investigated in this study, to clarify the co-loading effects on the sensing properties as adsorption/combustion-type gas sensors to ethanol or toluene. The 1Pt/10CeO₂-mp-Al₂O₃ showed the highest oxidation activity to ethanol. On the other hand, the TPD spectrum obtained from toluene-preadsorbed 1Pt/10Bi₂O₃-mp-Al₂O₃ showed the largest amount of CO₂ and a small amount of benzene at temperatures higher than 300˚C, among all samples. These properties are well correlated with the enhancement in the ethanol or toluene response by the co-loading of CeO₂ or Bi₂O₃ with Pt onto mp-Al₂O₃ as a sensing material of adsorption/combustion-type gas sensors, respectively.

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42.

A high performance miniaturized catalytic combustion sensor has been developed for the detection of methane. The sensor consists of two catalytic layers with different porous structures and catalysts, which improve long-term stability and durability against poisoning gases. The sensor showed good sensing performance and long-term stability for more than two years.

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43.

A new catalytic combustion-type CO gas sensor was devised by using Pt-loaded apatite-type oxide solid solution (11wt%Pt/La_9.0Si_5.8Mn_0.2O₂₇) as the CO oxidizing catalyst. Since the present catalyst can oxidize CO at 60 °C, the sensor responded toward CO at the temperatures above 60 °C. With increasing the operation temperature, the sensor exhibited smooth and reproducible response to CO gas and realized the rapid response of 10-20 s in 50% response time at 130 °C. Moreover, since the present sensor showed linear response to CO gas concentration change, it is expected that the sensor can detect CO quantitatively at 130 °C.

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44.

Catalytic oxidation of solids by solid catalysts is a three-phase reaction between solid reactants, solid catalysts and gaseous molecules (O₂). Therefore, the catalyst activity is affected by the contact condition between the solid reactants and the solid catalysts. Moreover, in contrast to gaseous reactants, the solid reactants cannot diffuse and adsorb on the catalyst surface. This makes it difficult to evaluate the activity of solid catalysts and detection of carbon combustion reaction. In this research, focusing attention on carbon dioxide generation and oxygen partial pressure changes caused by carbon combustion and aims to establish a technique for measuring the local oxygen concentration changes caused by carbon combustion using the zirconia oxygen sensor coated with CeO₂ catalyst. By applying this technique, it was carried out basic experiments aimed at solid reactant sensor development of new principles for quantitatively detecting the amount of CB from local oxygen partial pressure changes caused by the CB combustion on the zirconia oxygen sensor diffusion layer.

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45.

YSZ-based gas sensors using a dense Au (d-Au), a porous Au (p-Au) and Au added with one of oxides (MO) such as CeO₂, Gd₂O₃, Pr₆O₁₁, La₂O₃ and Sm₂O₃ in 4 wt% as a sensing electrode (SE) and Pt as a reference electrode, which were denoted as d-Au/Pt, p-Au/Pt, and Au(4MO)/Pt, respectively, were fabricated, and the effects of the MO addition into the Au SE on the sensing properties to toluene (50 ppm) were especially examined in this study. The MO addition into the Au SE increased the porosity, and then enhanced the toluene response properties. However, the magnitude of toluene response of the Au(4MO)/Pt sensors was smaller than that of the p-Au/Pt sensor, probably because the MO powders in the SE promoted catalytic oxidation of toluene and thus reduced the toluene concentration at triple phase boundaries (electrode/YSZ/gas) at the bottom of the Au(4MO) electrode. In addition, the response speed of all the Au(4MO)/Pt sensors was comparable to that of the p-Au/Pt sensor, while the recovery speed of all the Au(4MO)/Pt sensors was faster than that of the p-Au/Pt sensor. The excellent recovery speed may originate from the fact that the MO powders effectively burn out residual toluene in the SE. The Au(4CeO₂)/Pt sensor showed the largest toluene response among all the Au(4MO)/Pt sensors, owing to the highest electrochemical oxidation activity of toluene at the Au(4CeO₂) SE.

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46.

An impedancemetric solid-state NOx sensor was tried to be investigated using a zeolite as a receptor and a lithium ion conductive electrolyte as a transducer, respectively. Change in micropore distribution, gas adsorption, and desorption properties of the zeolites were observed with cation-exchange of the zeolites. It found that the impedance properties of the sensor devices changed with depending on NO₂ concentration. Among them, the sensor with Y type zeolite with potassium ion-exchange as a receptor showed the highest sensitivity to NO₂. This sensor response properties were better than the other sensors attached with ferrierite or L types of zeolites which micropores were smaller than that of Y type. These results also indicated that the sensor devices using electrolyte transducer make it possible to apply an insulation compound as a receptor material.

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47.

Potentiometric gas sensors using N-loaded SnO₂ (nN/SnO₂(Tm), N: noble metal (Pt or Au), n: the amount of N loading (2 (wt%)), T: heat-treatment temperature, m: heat-treatment atmosphere) as a sensing-electrode material and an anion-conducting polymer (ACP) electrolyte (EC(2N/SnO₂(Tm))) have been fabricated, and effects of the Pt loading onto SnO₂ on the CO-sensing properties have been investigated in this study, compared with those of the Au loading. The loading of Pt or Au onto SnO₂ largely enhanced both the CO and H₂ responses irrespective of the heat-treatment conditions, and the EC(2Pt/SnO₂(500air)) sensor showed excellent CO selectivity against H₂, in comparison with the EC(2Au/SnO₂(400air)) sensor. On the other hand, the heat treatment in H₂ at 250°C reduced the H₂ response of the EC(2Au/SnO₂(Tm)) sensor and thus largely improved the CO selectivity against H₂, while it was ineffective in improving the CO selectivity of the EC(2Pt/SnO₂(Tm)) sensor. However, the CO selectivity of the EC(2Au/SnO₂(250H₂)) sensor against H₂ was deteriorated after 3-week storage under normal atmosphere, while the CO selectivity of the EC(2Pt/SnO₂(500air)) sensor against H₂ after the 3-week storage was quite comparable to that of the as-prepared EC(2Pt/SnO₂(500air)) sensor.

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