Vol. 29, Supplement B (2013)

1.

Measurement of blood amino acids is useful for the diagnostic and health-care of congenital metabolic diseases. Ninhydrin reaction-coupled HPLC analysis is conventionally used to amino acids detection. However, the present method is complicated and time-consuming. In this study, we paid attention to glycine oxidase ( GlyOx ) to make Gly sensor for the diagnostic and health-care of hyperglycinemia patients. The enzyme and the electron mediator were dropped onto the working electrode of a screen-printed carbon electrode and dried in turns. Ferrocenmethanol was used as the electron mediator. The Gly sensor was characterized for the Gly concentration dependence and the substrate specificity. The sensor measurement was performed by the chronoamperometry at 0.5V with a mini-potentiostat. Gly detection was achieved in the concentration range from 10 to 200 µM by measurement of the oxidation current.

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2.

Carbon based nanomaterials such as carbon nanotube (CNT) and carbon nanofiber (CNF) have been studied for application to fuel cells and various biosensors. We have greatly improved the direct electron transfer (DET) of enzymes on a nanostructured carbon film or CNF modified film electrode by employing the one-step UV/ozone treatment of these carbon materials. This treatment changed the CNF surface from hydrophobic to hydrophilic because a sufficient quantity of oxygen-containing functional groups was introduced onto the CNF surface. Furthermore, this simple and mild approach increased both the effective surface area and the number of edge-plane defect sites. As a result, we obtained the highly efficient DET of bilirubin oxidase (BOD), cytochrome c and cytochrome P450 (CYP) on the treated CNF modified electrode. For example, the oxygen reduction current of BOD on the treated CNF modified electrode was about 38 times higher than that on an untreated CNF-modified electrode. These results indicate that the combination of nanostructured carbon and a simple UV/ozone treatment process can efficiently create a functionalized surface for the electron transfer of enzymes, which provides an excellent opportunity for the development of new generations of enzyme based biosensor such as drug metabolism sensors through CYP

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3.

A polymer reactor containing glycogen phosphorylase b immobilized onto the carbon fibers　modified chemically was applied to a flow-injection system for determination of adenosine monophosphate. Performance characteristics as the enzyme sensor were tested.

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4.

Glucose sensor having sensing region inside the tip of a fine tube was fabricated using fine tapered stainless needle, which its tip diameter was 0.23 mm. Platinum film was coated inside the tube by electroplating and the outside was covered with insulating films of silica and polyimide using perhydropolysilazane and soluble polyimide solution, respectively. The enzyme glucose oxidase was immobilized on the platinum surface located inside the tube by first electrodeposition of enzyme, followed by the electropolymerization of o-phenylenediamine. Amperometric responses of the prepared electrodes to glucose were examined by measuring the electrooxidation current at a potential of 0.60 V (for hydrogen peroxide detection) in 0.1 mol dm-3 phosphate buffer solution (pH 7.4). The obtained sensor showed good response with sufficient linear relationship between response current and glucose concentration.

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5.

Glucose oxidase-immobilized electrodes were prepared by the combination of electrodeposition and photopolymerization. Hexyl methacrylate (HMA) and 1,6–hexandiol dimethacrylate (HDMA) were employed as photo-polymeriable methacrylates and were added in the enzyme-electrdeposition solution, in order to be entrapped in the enzyme film. Water soluble initiator, 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide was also added in electrdeposition solution. After the electrodeposition of enzyme, obtained enzyme film containing methacrylate was photo-polymerized using Xe flash lamp. All obtained electrodes performed as glucose sensors and the stability of the enzyme film were improved by UV radiation. Electrode prepared using HDMA showed higher long-stability than that prepared using HMA.

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6.

Binding interaction of acridine orange （AO） with tyrosinase （TYR） was investigated by steady-state fluorescence spectroscopy in combination with UV-vis absorption and circular dichroism （CD） spectroscopy. UV-vis absorption and steady-state fluorescence spectroscopy suggest that AO rapidly binds to TYR and forms stable complex. Based on the AO-induced fluorescence quenching data, the binding constant KA was estimated to be 1.9 x 10⁵ M^-1 at 298 K. The thermodynamic parameters (ΔH, ΔS, ΔG) obtained by Vant' Hoff plot indicates that the binding reaction is entropy-driven spontaneous process and that both hydrophobic and electrostatic forces play important roles in the binding process between AO and TYR. Synchronous fluorescence spectra suggests that the microenvironment around the buried Trp-residue is slightly distorted in the presence of AO （i.e., polarity around the Trp-residue was increased）. Furthermore, CD spectra at far-UV region of TYR demonstrated that the secondary structure of TYR is altered in the presence of AO with reduced α-helix contents.

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7.

Surface Plasmon resonance (SPR) sensor is highly sensitve mass transduder. In order to provide selectivity, a biomolecule recognition element (e.g. antibody, antigen, enzyme etc.) is attached onto the sensor surface. In our research, SPR immunosensor for detection of the illegal compound, clenbuterol, containing in food import has been developed. The immunosensor employed indirect competitive inhibition assay format. Succinimide group terminated alkanethiol was used for immobilization of clenbuterol. It was found that clenbuterol and ethanolamine formed domain structure in nanometer order. Each domain size was approximately 10 nm x 10 nm, which was corresponding to the domain size of "laid-on" and "standing" of succinimide groups terminated alkanethiol monolayer. The ratio of "laid-on" and "standing" succinimide groups was almost the same as that of ethanolamine and clenbuterol at the sensor chip. The surface structures in molecular scale were characterized by electrochemical methods, scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and FT-IR RAS.

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8.

We have examined to expand the ability of an acid sensor for determining the titratable acidity in shochu, sake, and coffee. The detection is based on the prepeak current attributed to the reduction of 3,5-di-tert-butyl 1,2-benzoquinone (DBBQ) in the presence of acids, such as, acetic acid, chlorogenic acid. It was important for monitoring the acidity of each sample to prepare the quinone solution being a proper composition of DBBQ, NaCl, and acid at the appropriate concentration. The shochu sensor can determine the acidity from 0.09 to 4.0. The titratable acidity of sake by the sensor was compared with that determined by the potentiometric titration using 0.1 M NaOH. The correlation coefficient of the both results was more than 0.9.

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9.

The light-addressable potentiometric sensor (LAPS) is a semiconductor-based bio-chemical sensor which is able to detect the concentration of certain bio-chemical species in a spatially resolved manner by utilizing a light probe. Since light addressability has equipped it with the new feature of imaging ability to visualize the distribution pattern of bio-chemical species, tremendous work has been made to improve the imaging performance of LAPS (resolution, speed of measurement etc.). In this research, the idea of facilitating device-level simulation instead of an equivalent-circuit-model derivation will be presented for analyzing the factors (doping and thickness of the Si substrate, insulating layer, wavelength and modulation frequency of the illumination, etc.) that have effects on it, especially its spatial resolution. To lay the foundation for analyzing the spatial resolution, the minority carrier distribution under illumination has been obtained. Furthermore, investigation on the spatial resolution by realizing the device-level model of photocurrent response to the surface potential pattern has been performed successfully.

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10.

Subclinical mastitis is an infectious disease of dairy cows. For the early diagnosis of this disease, we have already reported an on-site diagnostic device on the basis of the detection of superoxide anion (O₂⁻) secreted from neutrophils in mastitic milk. To improve detection sensitivity and selectivity further, we propose a novel method that uses sensitivity enhancement by metal deposition on a single electrode and coulometry that follows. The electron transfer from O₂⁻ secreted from neutrophils through SOD to the electrode in a flow channel and the deposition of copper in the other flow channel occurred spontaneously, whereas the oxidation of H₂O₂ did not occur. The novel method and device could enhance the sensitivity of electrochemical detection of O₂⁻ secreted from neutrophils for the on-site diagnosis of subclinical mastitis. The lower detection limit of the number of neutrophils was 7.7 × 10⁴ cells/mL.

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清山賞受賞講演1

We have developed biosensing systems with rapidity, simplicity and highly-sensitivity based on a scanning electrochemical microscopy (SECM), dielectrophoresis and chemical amplification method. SECM has been applied to image the distribution of molecules in the localized area and quantify the activity and function of single cell. Dielectrophoresis has been used to fabricate pattern with particles and cells and applied it to develop a simple and rapid immunosensing system. A novel immunosensing method has been developed on the basis of the sensitive determination of a product generated by an enzyme reaction with dual amplification system combining an electrochemical-redox cycling and coulometric signal transduction using a galvanic cell.

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清山賞受賞講演2

The dynamic property of a soft matter on the solid-liquid interface oscillating at MHz was investigated in detail. Especially, we focused on the molecule length moving with the oscillating plate, resonant length, in physical and chemical adsorption. In physical adsorption, we used polyethylene glycol (PEG) as a soft matter and systematically varied the number-average molecular weights of PEG molecules over 4 orders of magnitude. The analysis on the basis of the Debye process reveals that the resonant length of PEG at 9 MHz is 5.4nm. On the other hand, in chemical adsorption, we used the 7 types of mercapto oligo(ethylene glycol) methyl ethers, HS(CHM₂CH₂O)nCH₃. The systematical analysis on the basis of the Voight model reveals that the resonant length is 8.8 nm. As a result, we find that the physically adsorbed molecules of polyethylene glycol slip on the solid-liquid interface oscillating at MHz.

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11.

We present estimation of enzyme activities immobilized on PDMS by using the Bio-LSI system consisted of 400 (20×20) measurement units in 5×5 mm area. The PDMS substrates modified with glucose oxidase (GOx) or lactate oxydase (LOx) were mounted on the Bio-LSI immersed in the solution containing 10 mM glucose or lactate. When potential (+0.7 V) was applied to all electrodes in Bio-LSI, to oxidize hydrogen peroxide generated by the enzyme reactions, the oxidation responses increased at the measurement units corresponded to the GOx or LOx spots. We also utilized the present system to develop an immunosensor. Line patterns with anti-mouse IgG antibody were prepared on PDMS substrates. Another PDMS with 4 channels were mounted on the PDMS substrates by 90° relative to the lower line with antibody. The solutions containing different concentrations of model analyte (mouse IgG) were introduced into each channel to form the immuno-complex at the intersections. After the PDMS substrates were treated with GOx labeled antibody, activities of the immobilized GOx were measured simultaneously by the Bio-LSI. The current response increased with increasing the concentration of mouse IgG.

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12.

Microfluidic paper-based analytical devices (µPADs) draw attention as a new class of point-of-care (POC) diagnostic devices that are inexpensive, easy to use, and designed specifically for use. However, it's difficult that µPADs is applied to the diagnosis based on quantitative analyses of low concentration. Therefore, µPADs has limited the development of application to bioassay of the low-concentration region. Our aims is to achieve accurate quantitative analysis of low concentration in a new-type microfluidic devices which have had the same function as µPADs like inexpensive and easy to use. Whereas the conventional microchannel of µPADs are fabricated in a paper, impregnating with photoresist, dried, and exposed to UV light through a transparency mask, the microchannel in this study are fabricated in colored transparent film and double-sided tape as impermeable barrier. In comparison with detection in nitrocellulose paper commonly-used as the substrate of µPADs, our microfluidic devices were able to detect a tenfold higher sensitivity in low concentration range.

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13.

Femtosecond laser ablation is the process of removing material from a solid by irradiating a polymer substrate with a high-intensity ultra-fast laser beam, thereby causing surface modification to manipulate biological component. Ink-jet printing is a preferred method of dispensing liquid micro-droplets, offering the precise volumetric control, high speed deposition and low environmental impact. Towards industrial use, the process through the combination of these two technologies have the advantages of high accuracy, low cost and semi-automatic system. In this study, multiple single immunoassay chip was fabricated on the basis of this process, and then we compared the performance of our chip has been developed and commercially available chip that is chemically surface-treated.　As a result, we got the sensitivity and accuracy comparable to the chip of expensive commercial.

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14.

We propose a new concept for autonomous microfluidic systems. A bubble-based micropump that moved a solution forward and backward was constructed with three flow channels in which platinum black, zinc, and silver electrodes connected with each other. To switch the injection of solutions, electrowetting-based valves consisting of gold and zinc were used. The valves opened when an electrolyte solution reached the zinc part in a controlling flow channel. Timing circuits that opened the valves at predetermined times were also fabricated and were used for sequential operation of the pumps.

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15.

We report that blood coagulation generates both fibrin and low-refractive index ingredients (LRI) by using a SPR (Surface Plasmon Resonance)-based microfluidic sensor. We performed blood coagulation monitoring using a uneven crossing microchannel to make a coagulation trigger reagent and a plasma sample remain stationary during coagulation. It is well known that fibrin is last product of a blood coagulation cascade, however, LRI generation is another phenomenon. LRI generates shortly subsequent to contact the plasma sample with the reagent at the interface between them. We also confirmed that the amount of LRI generation is correlation to coagulation activity rate of plasma samples.

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16.

We have recently applied the fluorescence resonance energy transfer(FRET) observation of Yellow Cameleon(YC) expressed mammalian cells to measure intracellular Ca²⁺ concentration without any probe reagents. On the other hand, the intracellular reaction accompanied by the depolarization response of PC12 cells as a model nerve precursor cell, which were adhered on an Au sensor chip to high K⁺ stimulus was observed by the reflection intensity change in the individual cell regions with a two dimensional surface plasmon resonance(2D-SPR) imager with high resolution at real-time. We considered that translocation of activated PKC to cell membrane adhered on a gold chip was observed by refractive index change. In this study, we tried to observe the response of YC expressed PC12 cells to acetylcholine receptor agonist simulation by using FRET and 2D-SPR imaging. These results suggested future wide applications of label-free cell-based drug sensing by using these techniques.

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17.

This study presents a novel shadow imaging technique for cell counting. This technique is accomplished through the use of a single-cell array fabricated on an image sensor, complementary metal oxide semiconductor (CMOS) sensor. The single-cell array is constructed by using microcavities periodically-arrayed in a metal plane substrate. When the microcavity array is illuminated from above, only the light transmitted through the microcavities is received by the sensor, resulting in a grid-like pattern image consisting of the periodically-arrayed bright spots. In this set up, the spots of trapped cell are visualized as shadow blocks in the image owing to light absorption by the cell. Our proposed cell counting method employs enumeration of the shadow blocks. Using this platform, all cell counting processes, including construction of the single-cell array and image acquisition, were implemented in a single integrated device. Furthermore, multi-color imaging of fluorescent labeled cells was successfully performed. This system is expected to provide a novel miniaturized cell counter that enables rapid cell counting and cell profiling.

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18.

In this study, a hydrogel-based oxygen sensor sheet was developed for in vitro assay of contraction-dependent regulation of oxygen consumption activity in skeletal muscle cells. This soft, molecularly permeable hydrogel-based sensor was directly laminated to another hydrogel on which myotubes were micropatterned, and displayed usefully measureable changes in local oxygen consumption activity of myotubes upon electrically-induced contraction. This bioassay system will allow the study of exercise-dependent glycemic control via mitochondrial energy production in exercised skeletal muscle cells and will help us to understand the mechanism of exercise therapy for type 2 diabetes.

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19.

Control of blood-coagulation is very important for safe operation of extra corporeal circulation. However suitable technology for monitoring anticoagulant in blood is yet to be developed. The purpose of this study is development of a sensor for level of heparin, which is the most well-used coagulant, using an electrode grafted with heparin-imprinted polymer. Indium-tin oxide (ITO) electrode was grafted with poly (methacryloxyethyl trimethylamine chloride-co-acrylamide-co-methylenebisacrylamide) in the presence of heparin. A cyclic voltammetry was performed with the grafted electrode. The anodic current was sensitive to the heparin but has serious hysteresis. Washing of the electrode by 1-M sodium chloride solution was effective to cancel the hysteresis.

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20.

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 the blended MBAA and EDMA at the ratio of 1:1 or 1:2 indicates chiral-selective sensitivity with the template. As a result, blending crosslinking monomers is effective for enhancing selectivity of the gate effect of MIP.

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21.

We have developed Bio-LSI systems for a highly sensitive and real-time amperometric bio-imaging platform with 400 sensor electrodes. The 2^nd generation Bio-LSI has a function to select the operation of the 400 electrodes individually from 4 modes; off, electrometer, V1 and V2. In this study, we utilized this function to selective modification of electrodes by Peroxidase/Os-polymer (Os-HRP; BAS Inc.) for the simultaneous detection of hydrogen peroxide and oxygen on one chip. We successfully electrodeposited the Os-HRP on the selected electrodes by cycling of the electrode potential from −0.4 V to 1.0 V for 25 or 50 times using V1 mode. From the cyclic voltammograms in PBS, the surface concentrations of the Os complex were calculated to 1.0 nmol/cm² and 1.2 nmol/cm² for the 25 and 50 cycle deposited electrode, respectively. The Os-HRP deposited electrodes showed obvious chronoamperometric responses for successive addition of 10 μM hydrogen peroxide (final concentration), while the non-deposited electrodes did not show any significant responses.

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22.

We have employed poly(allylamine)-containing manganese oxides (PAAm-MnO₂), which is one of the anion insertion materials, as inner contacting layers for all-solid-state chloride ion-selective electrodes with ion-selective membranes. In this study, the PAAm-MnO₂ layer having nitrate ion exchange ability was further applied for all-solid-state nitrate ion-selective electrodes. The Pt / PAAm-MnO₂ electrodes can insert/extract nitrate ion reversibly in electrochemical processes and show stable potential response to nitrate ion activity in KNO₃ aqueous solution. Moreover, the double layered electrode with additional nitrate ion-selective membrane, i.e., Pt / PAAm-MnO₂ / PVC, demonstrates quicker and more stable Nernstian response in a wide range of nitrate ion activity, compared with those of the Pt / PAAm-MnO₂ electrodes. AC impedance analysis reveals that the embedded PAAm-MnO₂ layers bring a reduction of the resistance of the electrode, indicating that the layers makes superior ionic and electronic communication possible at the interface between the Pt substrate and the ion-membrane.

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23.

Determination of nitrite-ion concentration　has been becoming important for the control of eutrophication in close water system. In this study, it was aimed to develop a high sensitive electrochemical nitrite-ion sensor using a chemical stable perovskite-type oxide thick-film. Perovskite-type oxide ABO₃ (A = La, Sm, Gd, B = Cr, Mn, Fe, Co) powders were prepared by a polymer precursor method. The thick-film sensor devices were prepared by an electrophoretic deposition (EPD) method on the carbon　substrate. Among the sensor devices tested, the SmFeO₃ thick-film showed the linear response to nitrite-ion between 1.0×10^-5 M and 1.0×10^-4 M with good selectivity under O₂ saturated condition. The sensor responses were influenced by O₂ concentration in sample solution, which should relate to sensing mechanism of this sensor.

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24.

Lithium insertion materials have been widely studied as positive active materials for lithium ion batteries. In this study, four lithium insertion materials, i.e., LiCoO₂, LiFePO₄, LiV₃O₈, and LiMn₂O₄, have been employed as inner contacting layers for the all-solid-state lithium ion-selective electrodes, which are covered with the outer lithium ion-selective membrane containing ionophore. Electrochemical measurements revealed that the installation of an inner layer of LiFePO₄ bring quicker Nernstian response to lithium ion activity, demonstrating better potential stability, compared with those of the other insertion materials. One of the key factors to select the insertion materials for the electrodes in aqueous system is that the insertion material has superior insertion/extraction behavior of lithium ion in the range of potential window of H₂O.

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25.

An sp² and sp³ hybrid carbon film electrode was utilized for electrochemical measurement of Cd and Pb at ng/ml (ppb) level concentrations. Heavy metals (Cd, Pb) are threat to human health due to the fact that they are not biodegrade and metabolizable. That is why the determination of Cd and Pb is important. We have recently proposed and examined a new-type sp² and sp³ hybrid carbon film electrode using sputtering method. The carbon film was formed by employing the Unbalanced Magnetron Sputtering method, and has a nano-crystalline sp² and sp³ mixed bond structure with an atomically flat surface. In addition, it has a wide potential window, which is an advantageous for ASV. Composition of solution was optimized and the calibration curve was prepared. The results obtained with our electrodes were compared with those obtained with a commercially available glassy carbon (GC) electrode. The detection limits of Cd and Pb were 0.5 ng/ml (0.5 ppb) and 50 ng/ml (50 ppb), respectively. The preconcentrated Cd and Pb on the electrode surface were observed with Kelvin probe force microscopy while observing the morphology change with an atomic force microscope and a scanning electron microscope. The preconcentrated Cd or Pb on the sp² and sp³ hybrid carbon electrode was revealed to be a thin sheet structure, which was significantly different from the Cd or Pb on a conventional carbon material that grows with a coralloid structure. We also applied our electrode for quantitative detection of heavy metals in pond water samples.

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26.

Solid electrolyte-type planar gas sensors using NASICON (Na₃Zr₂Si₂PO₁₂) disc attached with Pt mixed with Bi₂O₃ as a sensing electrode (Pt(nBi₂O₃), n (0.01 or 1): the amount of Bi₂O₃ addition (wt%)) were fabricated, and then their sensing properties to 300 ppm CO and H₂ were investigated at the operating temperatures of 25~300ºC in dry air. The CO response of the sensor with Pt(1Bi₂O₃) was larger than that of the sensor with Pt(0.01Bi₂O₃). In addition, the CO response of the sensor with Pt(1Bi₂O₃) was comparable with the H₂ response at 300ºC. The CO and H₂ responses of the sensor with Pt(1Bi₂O₃) increased and decreased with a decrease in the operating temperatures, respectively, and thus the CO response was about six times larger than the H₂ response at 25ºC. It was found that the large amount of Bi₂O₃ addition effectively improved the magnitude of CO response as well as CO selectivity against H₂ at lower temperatures.

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27.

Potentiometric NO₂ sensors operative at room temperature were fabricated by using a solid-state electrolyte (NASICON (Na₃Zr₂Si₂PO₁₂) or Li+-conductor (LiTi₂(PO₄)₃)) with ITO (indium tin oxide) and an auxiliary phase (NaNO₂, NaNO₃, NaNO₂-In₂O₃ (2:1, 3:1, 4:1 in molar ratio) or NaNO₂-BaSO₄, NaNO₃-BaSO₄ (2:1 in molar ratio)) sensing electrode. Their NO₂ sensing properties were examined in the range of 0 – 7 ppmNO₂ under 30 %RH (relative humidity) at 30 oC. Among the NO₂ sensors examined, Li⁺-conductor-based sensor attached with ITO and NaNO₃ auxiliary phase demonstrated fairly good NO₂ sensing properties and its EMFs (electromotive force) were proportional to the logarithm of NO₂ concentration. When the NO₂ concentration increased from 0 to 7 ppm, the EMF change was about 320 mV in 500 ppm CO₂ and the 90 % response time of the sensor was within 15 min to the increase in NO₂concentration from 2 to 3 ppm. Also, the sensor was not almost affected in the range of 0 – 2500ppm CO₂ concentration.

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28.

The effect of Au sputtering to an oxide-disc/YSZ (yttria-stabilized zirconia) interface on the gas sensing performance was evaluated. The YSZ-based sensor using a SnO₂-disc sensing-electrode (SE) gave high sensitivities to C3H6, C₃H₈, CO and H₂, but low sensitivities to CH₄, NH₃, NO and NO₂, at 550ºC. It was found that Au sputtering to SnO₂-disc/YSZ interface brought about the significant increase in NH₃ sensitivity, while the sensitivities to other gases decreased largely, under the same conditions. It was also revealed that the SnO₂/Au-SE gave a selective response to NH₃ especially at operating temperature of 600ºC. The comparison of modified polarization curves measured in 21 vol.% O₂ and in 100 ppm NH₃ for the present sensor suggested that the Au sputtering drastically improved the electrochemical catalytic activities especially to NH₃, resulting in an increase of NH₃ sensitivity. SEM observation showed that Au particles were dispersed uniformly on the SnO₂ layer near the SnO₂/YSZ interface.

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29.

A sensing device for sensitive and selective H₂ detection was obtained by using yttria-stabilized zirconia (YSZ) as a solid electrolyte and ZnO(+ 84 wt.% Ta₂O₅) as a sensing electrode (SE) material. The response to H₂ was found to increase significantly and stabilized after aging for 40 days at 500oC. The effect of aging on the sensing characteristic was studied by examining the change in physical and chemical properties of SE before and after aging. XRD measurements confirmed that the crystal structure of SE was unaffected by aging. However, SEM observation for both samples showed a decrease in porosity and an increase of particle size after aging. In addition, the shifts in binding energy of the SE elements for the aged sample are believed to contribute to the change in catalytic activities toward the chemical reactions involved in the sensing signal generation, which are evidently also in favor to the enhancement of H₂ sensitivity and selectivity.

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30.

CO sensing properties of electrochemical gas sensors using noble metal (M)-loaded carbon black (CB) or In₂O₃ as an electrode material and an anion-conducting polymer (ACP) as an electrolyte (EC(nM/A-ACP) (n: the amount of M addition (1 or 2 wt%), M: Au or Pd, A: CB or In₂O₃)) were investigated in this study. EC(1Pd/CB-ACP) showed relatively large responses to both 500 ppm CO (ca. 46 mV) and 500 ppm H₂ (ca. 36 mV). On the other hand, the responses to 500 ppm CO of EC(2Au/In₂O₃-ACP) and EC(2Pd/In₂O₃-ACP) were larger than that of the EC(1Pd/CB-ACP), while their responses to 500 ppm H₂ were smaller than that of the EC(1Pd/CB-ACP). Especially, the EC(2Au/In₂O₃-ACP) showed the smallest response to 500 ppm H₂ (ca. 2 mV). In addition, the EC(2Au/In₂O₃-ACP) showed excellent CO sensitivity (ca. 33.5 mV/decade) and CO selectivity against H₂ in a wide concentration range of 10~3000 ppm CO and H₂.

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31.

The resistive type SO₂ sensor using V₂O₅/WO₃/TiO₂ (VWT) has been reported to have a good response to SO₂. However, it responded to NO and NH₃ largely. In this study, we placed a Pt/alumina layer on a VWT layer of the SO₂ sensor to decrease the response to NO or NH₃. The sensor response to SO₂ is hardly affected by the Pt/alumina layer in the case of VWT sensor with 3.0wt% V₂O₅ using Au electrode, while the Pt/alumina layer affects the response of other VWT sensors. The VWT sensor (3.0wt% V₂O₅) using Au electrode with the Pt/alumina layer shows smaller response to CO, H₂, H₂O, NH₃, and NO than that without the Pt/alumina layer. It is clarified that the Pt/alumina layer has a potential to improve the selectivity of the VWT sensor.

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32.

SmFeO₃ has been proposed as a gas sensing material to detect ozone, NO₂ and VOCs. 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. This sensitivity enhancement would suggest that the Sm on the surface acts as a toluene adsorption site and increase toluene concentration on the sensing film. The catalytic activity of SmFeO₃ to toluene oxidation was also significantly enhanced with the Sm-loading. This result may support the result of the toluene sensing.

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33.

For proposing the detection model of sulfur gases on multi-walled carbon nanotubes (MWCNTs) array sensor, we investigated the effect of defective carbon on resistance in air (Ra) and resistance change (RC) to 1 ppm sulfur gases, and the role of nickel particles at the tip of MWCNTs array on formation of p-n junction. The surface of nickel particles could be oxidized in air to be nickel oxide (p-type NiO). When exposed to 1 ppm hydrogen sulfide (H₂S), the oxide thin film was sulfidized at higher operating temperature (<200 oC). The formation of n-type NiS on p-type NiO could contribute to enhance space charge broadening by the formation of p-n junction at the interface of NiO and NiS. The space charge could be broadening to the whole of MWCNTs array. This broadening would affect the conductive pass between Au interdigitated electrodes at the bottom of MWCNTs array. Consequently, the MWCNTs array could play a role of gas adsorption antenna.

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34.

The electronic structures of undoped TiO₂ with rutile, anatase and brookite structure and Zr-doped TiO₂ with an optimized anatase structure were calculated within the framework of the density functional theory (DFT)　by using modified Becke-Johnson (mBJ) exchange potential. For the calculation Zr-doped anatase, we built two kinds of supercells; Type-A and Type-B supersells consist of 48 and 12 atoms, respectively, and a centered Ti atom was substituted for an Zr atom. In the case of larger supersell (Type-A), Zr related states were located in the range higher than 3.1 eV from E_F. On the other hand in the case of smaller supersell (Type-B), Zr related states were located in the range higher than 2.8 eV from EF. In both cases, Most of Zr states were located in the range higher than about 5.0 eV.

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35.

A catalytic combustion type carbon monoxide gas sensor which can operate at low temperature was successfully developed by employing a Pt-loaded cerium oxide–zirconium oxide–tin oxide solid solution (Pt-loaded CeO₂–ZrO₂–SnO₂) as the novel oxidizing catalyst. Since the present catalyst can oxidize CO at low temperatures, the present catalytic combustion type sensor applying the 10 wt%Pt-loaded Ce_0.68Zr_0.17Sn_0.15O_2.0 solid exhibited smooth and reproducible response to CO gas at 70 °C, which is extraordinaly lower than that required for the operation of sensors with the conventional CO oxidation catalyst such as Pt/Al₂O₃ and Pd/Al₂O₃.

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36.

We have investigated Pt/Ti-gate Si-metal-oxide-semiconductor field-effect transistors (MOSFETs) from the viewpoints of hydrogen gas sensors and also mother devices of Pt-Ti-O-gate Si-metal-insulator-semiconductor field-effect transistor (MISFET) hydrogen gas sensors. The Pt/Ti-gate Si-MOSFETs with uniform coverage of Ti layers over the gate area do not respond to hydrogen gases in general. The observed large variations of threshold voltage V_th and sensing amplitude DV_g for the as-processed Pt (15 nm)/Ti (5 nm)-gate Si-MOSFETs originate from the initial unintentional oxygen invasion into the Ti layers at the beginning of phosphorus-doped silicon glass deposition. The air-annealed and succeeding hydrogen post-annealing procedure for Pt (15 nm)/Ti (5 nm)-gate Si-MOSFET hydrogen gas sensors recovers the uniformity of V_th distributions close to that of as-processed Pt (90 nm)/Ti (5 nm)-gate Si-MOSFETs and leads to a large sensing amplitude DV_g . We have found a critical V_th , V_thc , at which the response to hydrogen gas exposure begins. We have introduced a percolation model in which the ratio of Ti contact area to the effective Pt contact area over the gate oxides will be reduced to zero in accordance with the increasing dose of oxygen invasion, at a point which probably corresponds to V_thc .

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37.

In order to clear the mechanism of performance change based on the constant voltage processing, polarization curves of a working electrode and a counter electrode of a liquid electrolyte membrane type CO sensor were measured using Pt wire as a reference electrode. As a result, when the cathodic current of working electrode was decreased owing to the constant voltage processing, short-circuit current between both electrodes in the air containing CO is more than a half of the diffusion limited current of a CO oxidation reaction on the working electrode. This mechanism of performance change based on the change of cathodic current of working electrode can be described by using the model proposed by authors in a previous report.

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38.

An amperometric electrochemical sensor was investigated for the detection of low concentration of hydrogen(H2) leaking into the atmosphere. The demand of hydrogen leakage detection will increase with the expectation in a hydrogen energy society. The characteristics of the sensors showed that the difference in performance was dependent on the electrode materials. The small size sensor using gold electrode showed good selectivity and response for 100ppm of hydrogen gas. The sensors can be equipped in the portable type gas monitors.

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39.

We focused on enhancing sensitivity and response speed of optode-type sensor. When metal oxide films were used as sensing material, adsorbed oxygen species that are present on surface of the sensitive films would be excited by UV irradiation, and it is expected that the rate of response reaction and recovery reaction to the target gas is promoted. Therefore, in this study the effect of UV irradiation on the sensitive film was demonstrated using the reaction system of H₂ and WO₃ thin film prepared by sol-gel method. In the case of using hydrogen gas balanced with nitrogen as test gas, the recovery reaction rate was accelerated rather than the response reaction rate. In air atmosphere, both response and recovery rates were influenced by UV irradiation. Therefore, it is suggested that only the reaction involving oxygen was influence by UV irradiation. Furthermore, stacking of titanium oxide thin film as UV sensitive material on WO₃ film showed a significant effect of UV irradiation on reaction rate.

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40.

Fiber optic sensors, such as fiber Bragg gratings (FBG) sensors, have characteristics of lightweight, reliable, compact, etc. In this study, the authors have tried to apply FBG to hydrogen sensor. H₂ combustion over noble metal catalyst dispersed in oxide support causes reaction heat. The temperature change of the device is detected by FBG sensor. On the purpose of improving response, size and cost, hydrogen sensitive layer was directly immobilized on the periphery of the optic fiber. We employed Pt/WO₃ and Pt/SiO₂ as sensitive layer. It is found that Pt/SiO2-type sensor responded to more than 1 vol.% H₂ in air quickly, and 90% response time was under 30 seconds. On the other hand, Pt/WO₃ was difficult to immobilize on FBG.

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