Vol. 27, Supplement B (2011)

1.

Perovskite-type oxide Sm_1-xCa_xFeO₃ (x = 0, 0.05, 0.20, 1.0) thick-film devices were studied for an AC impedancemetric C₂H₂ sensor. The thick-film devices could be fabricated with perovskite-type oxide powders by a polymer precursor method calcined at 750 ℃. The paste mixed with oxide powder, PVP and α-turpentine were uniformly screen-printed on an Au-interdigitated electrodes and heat-treated at 850 ℃. Frequency and sensing characteristics of the obtained devices to various C₂H₂ concentrations were evaluated by means of an AC impedance method at PO₂=0.21. Ca-doped SmFeO₃ device showed decreasing impedance and appeared a response lag in frequency characteristics, however the Sm_0.80Ca_0.20FeO₃ device showed obvious improvement in capacitance, compared with non-doped SmFeO₃ device.

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2.

The conductance changes of an SmFeO₃ based p-type semiconductor gas sensor due to the contamination level of air with ozone were examined at 200-300℃. At the higher concentrations above 1 ppm, the conductance of SmFeO₃ in ozone had a tendency to saturate. In the lower concentration below 1 ppm ozone, the SmFeO₃ sensor showed good sensitivity but it was not responsive to ozone below 45 ppb. The response time from air to ozone was distinctly longer than the recovery time from ozone to air, and the recovery time became longer with the increasing ozone concentration. Based on these confirmed results, the sensor can distinguish the contamination levels of ozone, from very good (0-50 ppb), good (50-100 ppb), poor (100-200 ppb), to very poor (>200 ppb).

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3.

We have investigated H₂S–gas sensing properties of CeO₂ by means of an exhaust gas analysis, a direct current (DC) resistance analysis, and an alternating current (AC) impedance analysis. On humid air condition, it was confirmed that H₂S gas was oxidized into SO₂ at the operating temperature on the surface of CeO₂. The AC impedance spectra of the CeO₂ sensor elements have a semicircle and a small shoulder in the plot of Z' and Z'' plane. As the semicircle stand from almost zero position of real conductance (Z'), it can be assigned to the bulk impedance component. The shoulder can therefore be assigned to grain boundary and electrode interface components of the impedance. The Z' value of the bulk component is reversibly decreased by H₂S, indicating that the sensor response of CeO₂ is dominated by the change of bulk resistance, and the grain boundary and an electrode interface have almost no contributions in the case of CeO₂. A TEM image of CeO₂ grain boundary shows no amorphous phase and clear combination of grains.

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4.

Porous In₂O₃ (pr-In₂O₃) powders (pr-In₂O₃(M), M: In₂O₃ source (N: In(NO₃)₃，Cl: InCl₃)) as a NO₂ sensing material were prepared by ultrasonic-spray pyrolysis of In(NO₃)₃ or InCl₃ aqueous solution containing polymethylmethacrylate (PMMA) microspheres as a template. The suspension containing PMMA microspheres (average diameter: 39.6 nm) was prepared by the emulsion polymerization employing methyl methacrylate monomer as a polymer source, sodium lauryl sulfate as a surfactant and ammonium persulfate as an initiator. The pr-In₂O₃(N) (specific surface area (SSA): 19.1 m² g^-1) and the pr-In₂O₃(Cl) (SSA: 30.5 m² g^-1) consisted of large microspheres with well-developed spherical pores (main pore diameter: ca. 30 nm) and nanoparticles (≤ 20 nm in diameter), respectively. The NO₂ response of pr-In₂O₃(M) was much larger than that of dense In₂O₃ microspheres (SSA: 1.56 m² g^-1) prepared by ultrasonic-spray pyrolysis of PMMA microspheres-free In(NO₃)₃ aqueous solution.

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5.

For SnO₂ gas sensor, it is well known that the oxygen in air adsorbs on the surface of SnO₂, and it increases the electric resistance. In an earlier study, the electric resistance has linearity to the square root of oxygen partial pressure (P_O2), indicating that the oxygen adsorbs as O^-. On the other hand, it is reported that O^2- adsorption peak was observed in the ESR measurement. Thus the discussion on oxygen adsorption species still remains. In this study, we aimed to investigate the oxygen adsorption species by measuring the relationship between the electric resistance and P_O2 with or without water vapor. SnO₂ powder was obtained by calcination of hydrothermally treated SnO₂, and the thick film device was fabricated by screen printing method. The electric resistance was measured at 350℃ in different P_O2 with or without water vapor. The obtained results indicated that the oxygen molecule adsorbs as O^2- and O^- under dry and wet conditions, respectively.

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6.

For semiconductor gas sensors, tin oxide (SnO₂) has been one of the attractive materials because of its high sensitivity and chemical stability. For the high sensitivity, the crystalline size of SnO₂ is significantly important. In this study, we prepared the SnO₂ nanoparticles from a thermal decomposition of SnCl₄ in a mixture of triethylene glycol (TEG) and tetrabutylammonium hydroxide (TBAH) in order to investigate its gas sensing properties. As the result, the crystalline size of SnO₂ prepared in the mixture of TEG and TBAH was 4.0 nm. Surprisingly it was found that the crystalline size of SnO₂ did not increased significantly even after calcination at 600-900℃. The sensor device using SnO₂ particles prepared in the mixture of TEG and TBAH showed higher sensor response as compared to the sensor device using the SnO₂ particles from the hydrothermal treatment. Such an improvement in the sensor response seems to be caused by the minimizing of the SnO₂ crystalline. In addition, it can be presumed that the difference in the donor density of SnO₂ crystalline attributed to the improvement in the sensor response.

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7.

The CO sensing property of CuO-loaded SnO₂-In₂O₃ sensor was investigated in a reducing atmosphere. The sensor response to CO for 14mol%CuO/SnO₂-In₂O₃ (8/2) was much higher than that for CuO/SnO₂ in the range of 200-1000 ppm of CO concentration. XRD and TEM results of CuO-loaded SnO₂-In₂O₃ showed the high dispersion of CuO on SnO₂-In₂O₃ particles. Therefore, high sensor responses of CuO/SnO₂-In₂O₃ may be due to the high dispersion of CuO playing a role as sensing site.

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8.

In order to prevent drunken driving accidents, there is a strong demand for developing effective built-in type alcohol detection systems in automobiles. For this purpose, apart from the conventional breath alcohol detection method, detection of emitted alcohol concentration from palm skin can achieve an easy alcohol detection system in a normal car starting process. We have studied the application of high sensitivity semiconductor alcohol sensor for practical use and report the results.

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9.

Solid electrolyte type ammonia (NH₃) gas sensor was fabricated by using trivalent aluminum cation conducting solid electrolyte of (Al_0.2Zr_0.8)_20/19Nb(PO₄)₃ with NH₄⁺-β-gallate (NH₄⁺-Ga₁₁O₁₇) solid as the auxiliary sensing electrode and its ammonia gas sensing performance was investigated in a humid atmosphere. The present sensor showed an advanced sensing performance of continuous, quantitative and reproducible response that obeys the theoretical Nernst relationship even in a highly humidified atmosphere containing 4.2 vol% H₂O at 230 ℃. Therefore, the sensor with NH₄⁺-β-gallate auxiliary sensing electrode is expected to be a practical on-site NH₃ gas detecting tool.

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10.

The sensing characteristics of mixed-potential-type yttria-stabilized zirconia (YSZ)-based sensors using rod-type TiO₂ (rod-TiO₂) sensing electrodes (SEs), with or without the addition of nano-sized Pd particles (nano-Pd) were examined. It was observed that the sensitivity towards representative components of exhaust gases for a sensor utilizing a composite rod-TiO₂ (+1 wt.% Pd)-SE were found to be lower than that for a pure rod-TiO₂-SE. However, the composite electrode gave selective responses to CH₄ and C₃H₈, which are alkane group hydrocarbons (HCs), at 500℃ in the presence of 5 vol.% H₂O. It was revealed via BS-SEM observations and XRD measurements that the rod-TiO₂ (+1 wt.% Pd)-SE was comprised of PdO particles directly attached to rutile-phase TiO₂ rods. Through a parameterized investigation of the effects of both TiO₂ rod aspect ratio and nano-Pd additions, we believe that the selective response to alkane group HCs for the sensor using a rod-TiO₂ (+1 wt.% Pd)-SE is primarily derived from the catalytic activity for gas-phase reaction in the SE material consisting of PdO particles directly attached to rutile-type TiO₂ rods.

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11.

A new potentiometric VOCs sensor based on the zirconia-based electrochemical sensors was proposed and the sensing characteristic was examined at 350-450℃. At 350-450℃, the potentiometric VOC sensor, Pt/YSZ/Pt, was responsive to sub-ppm levels VOCs such as acetic acid, ethanol, methyl ethyl ketone, benzene, toluene, o- and p-xylene. The SiC layer with 5μm in thickness formed on the working Pt electrode by the electrophoretic deposition technique. The over-coating of the working electrode with fine SiC particles was effective to improve the sensitivity and the response behavior as a VOC sensor especially ethanol, benzene, toluene and p-xylene. It is considered that the SiC layer acted as an oxygen molecular sieving layer when the SiC layer was exposed to ethanol, benzene, toluene and p-xylene. Our VOC sensor modified by the SiC layer can detect some ten ppb levels ethanol, benzene, toluene and p-xylene at 400℃.

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12.

A yttria-stabilized zirconia (YSZ)-based sensor utilizing a novel Zn-Ta-O composite sensing-electrode (SE) was developed. The Zn-Ta-O composite was comprised of 70 wt.% ZnO and 30 wt.% Ta₂O₅ sintered together at 1000℃, which from amongst the examined composite mixing ratios, was found to display rather interesting gas sensing characteristics. The sensing characteristics of the sensor using this novel material were further explored by studying the effect of sintering temperature on gas sensing response. The sensor sintered at 1200℃ exhibited a selective and sensitive response towards NO₂. A linear relationship on a logarithmic scale was observed for sensor responses to increasing NO₂ concentration. This linear relationship indicated that the sensing mechanism of the developed sensor was consistent with mixed-potential theory.

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13.

The carbon oxidation activity and sensing performance of an electrochemical sensor using a dense and robust SnP₂O₇-SnO₂ composite ceramic as a solid electrolyte with a Pt+Sn_0.9In_0.1P₂O₇-mixed working electrode were investigated at an operating temperature of 200 °C. Specific reactivity of electrochemically formed active oxygen for carbon was accomplished along with a high current efficiency estimated from the four-electron reaction (C + 2H₂O → CO₂ + 4H⁺ + 4e^–). This reaction leaded to a linear relationship between the current signal of the sensor and the carbon content in the working. Moreover, an additional benefit of the present sensor on practical applications is that little interference was encountered in sensing for carbon at 1000 ppm CO and 1000 ppm C₃H₈ in the sample gas. The resulting amperometric mode sensor could successfully provide current signal corresponding to the quantity of particulate matter (PM) in a bench test apparatus. These results demonstrate that the present sensor continuously monitors the PM concentration while self-regenerating.

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14.

A solid electrolyte-type planar gas sensor attached with Au and Pt electrodes on one side of a NASICON (Na₃Zr₂Si₂PO₁₂) disc was fabricated and its inflammable gas (CO and H₂) sensing properties were investigated in this study. This sensor showed relatively large CO and H₂ responses at 350°C in dry synthetic air, low purity nitrogen (purity: 99.99%) and high purity nitrogen (purity: 99.9999%). This sensor showed negative and positive responses to CO in air and N₂, respectively, while it showed negative responses to H₂ under every atmosphere and the magnitude of the negative H₂ response decreased with a decrease in oxygen concentration in the atmosphere. Therefore, the oxidation reaction of CO and H₂ with O₂ seems to influence the electrode potential of Au and Pt in the air, but other reactions may also contribute to the change in the electrode potential of Au and Pt in N₂.

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15.

In our previous study, sensing properties for CO in various gas atmospheres were studied with amperometric sensor using 10wt%Au-In_0.95Sn_0.05O_1.5 cathode, RuO₂-La_0.6Sr_0.4CoO₃ anode and La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ electrolyte. In this study, planar type CO sensor which was consisted of anode and cathode on the same side was prepared and it was found that high sensitivity and selectivity was also exhibited on the planar type element. In particular, sensor is highly selective to CO and so selective detection of CO in exhaust gas from small boiler is expected by using this amperometric CO sensor. Effects of additives on active electrode was also studied and it was found that Ce(Mn,Fe)O₂ is effective for improving sensitivity.

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16.

La_0.8Sr_0.2AlO₃ was synthesized by spray pyrolysis method as a stable sensing-electrode (SE) material in high-temperature reduction condition for the zirconia-based amperometric type NOx sensor.　The X-ray diffraction pattern of the oxide powder after stability test was the same with the one of prepared oxide powder. From the I-V curve measurement, reduction current in 500 ppm NO₂ was larger than the current in the base gas. The sensitivity to 500 ppm NO₂ of the sensor was 1.3µA. The response and NO₂ concentration had a linear relation in the concentration range of 50-400 ppm. We concluded that La-Al based perovskite oxide has a possibility as an electrode material for the zirconia based NOx sensor.

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17.

New type solid electrolyte impedancemetric NOx (NOx ; NO, NO₂) sensor devices were designed by using nickel oxide (NiO) as a receptor, YSZ plate as a solid electrolyte transducer, respectively. The sensing performance of the impedancemetric NOx sensor was investigated for the detection of NOx in the range 10 ～ 150 ppm at 300 ~ 500 ℃. Nyquist plots of this sensor were measured at various concentrations of each NOx gases in range of 50 ~ 5 MHz. The sensitivities of these sensors were influenced by the ability of receptor materials to detect the gas at different NOx concentration. Here, we report the NOx sensing performance and the effect of receptor material of the impedancemetric solid electrolyte NOx sensor.

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18.

Anion-conducting polymers (ACP) are quite promising as an electrolyte of solid-polymer membrane fuel cells, because of their large OH^- conductivity. In this study, we have attempted to develop electrochemical H₂ sensors using ACP as an electrolyte. 10 wt% noble metal-loaded carbon black (M/CB, M: Au, Pd or Pt) or SnO₂ was mixed with an 5 wt% ACP isopropanol solution and the resulting paste was coated on the surface of both sides of an ACP membrane as sensing and counter electrodes. Among all sensors, an electrochemical sensor equipped with Pd/CB or SnO₂ as an electrode material for sensing and counter electrodes showed relatively large H₂ response.

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19.

Although the threshold voltages (Vth) of the as-processed Pt(15nm)/Ti(5nm)-gate Si-MOSFETs under same channel ion dose conditions show a large variation such as 0.846 V among several wafers, the air-annealing and succeeding hydrogen post-annealing procedure for the FETs hydrogen gas sensors leads to excellent uniform Vth distributions and large sensing amplitude ΔVg. The oxygen invasion process through Pt grain boundaries to amorphous Ti layers at 400℃ air-annealing for two hours is not a simple dopant diffusion process but super-heavily oxygen-doped process partly to grow nano-crystalline TiOx. The oxygen-invaded Ti layers change to a kind of new materials; novel mixing layers of nano-crystalline TiOx and super-heavily oxygen-doped amorphous Ti formed on SiO₂/Si substrates. The Ti mixing layers change from metals to semiconductors or insulators. As the Ti layers are so thin like 5 nm, the total amount of oxygen invaded into Ti layers will be saturated and stabilized. From the device operation point of view, it is crucial to control the Vth precisely that the Ti novel mixing layers are thin and fully depleted. This is supported by the facts that the Vth change before and after air-annealing procedures can be well explained by the difference of vacuum work function between Pt and Ti.

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20.

A clean energy system using hydrogen has been paid much attention. However, hydrogen is hazardous material because of its explosive nature. Therefore, the leakage detection of hydrogen is very important. The coloring reaction of noble metal, such as platinum supported WO₃ thin films with the exposure to hydrogen gas is well-known, and called gasochromism. In this research, gasochromic response of Pt/WO₃ thin films at wavelength of 1.3 μm as a hydrogen gas sensor was quantitatively evaluated. The optical transmittance measurements were conducted in airtight chamber at different temperature and humidity conditions. It is found that Gasochromic reaction was seriously inhibited in low temperature region and humid environment.

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21.

A fiber-optic biochemical gas sensor (bio-sniffer) for evaluation of indoor formaldehyde (FA) was fabricated and tested. Recently, chronic exposure of low level formaldehyde is associated with the risk of childhood allergy. Therefore, a high-sensitive and continuous sensor for formaldehyde vapor is required to maintain the healthy environment (< 20 ppb FA). For this purpose, fluorescence of reduced nicotinamide adenine dinucleotide (NADH) produced by reaction of formaldehyde dehydrogenase was utilized. The sensing probe consists of optical fiber probe, flow-cell and FALDH immobilized membrane. In order to prevent the FALDH immobilized membrane from deactivation in the gas phase, the enzyme membrane was fixed in a flow-cell in which phosphate buffer solution was circulated. The flow-cell also enabled to rinse reaction products and supplying NAD⁺. Therefore, the continuous measurement of formaldehyde vapor was achieved. As a result of characterization, a fluorescent signal increased immediately when FA vapor was applied and decreased to the initial value by the effect of buffer circulation when FA vapor was eliminated. 3.0 ppb to 500 ppb of formaldehyde vapor was detected. Consequently, the bio-sniffer was sufficiently sensitive and highly selective for application in indoor formaldehyde monitoring.

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外国人特別講演

An overview on different approaches for the construction of fully electro-active protein multilayers is given. The assembly is based on the layer-by-layer deposition of the redox protein cytochrome c and a negatively charged second building block on electrodes, which can be sulfonated polyanilline, carboxy-terminated gold nanoparticles or dsDNA. The unique property of these systems is the defined increase of electro-active protein amount with the number of deposited cyt c layers. These layered assemblies of a redox protein can be combined with enzymes in order to construct sensing electrodes for the enzyme substrate. Signal transfer can be achieved by direct protein-protein electron transfer without the need of external shuttle molecules. This can be shown for billirubin oxidase, laccase and sulfite oxidase.

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清山賞受賞講演1

Biomolecules, such as enzymes, are an efficient incomparable catalyst. The functionalities have been combined with electrochemical reaction to be bioelectronic devices. In the cases of the bio-macro-molecular interfaces, there are two interfaces on an electrode; a solution phase-enzyme layer interface and an enzyme layer-electrode interface. The interfaces act as a chemical reaction interface and a physicochemical reaction interface respectively. Efficient design and functionalization of the interfaces may elevate sensor ability and fields of applications. The author has studied the functional and physical structures of macromolecular interfaces in bioelectronics properties and others. The designed molecular interfaces also have been applied for new types of sensors, such as seamless cellular biosensor. The article has summarized current development about molecular interface and its application for biosensor designing.

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清山賞受賞講演2

High stability and robustness against sterilization are required for biosensors for artificial organs. However it is difficult for conventional biosensors using enzymes or antibodies to satisfy the requirements. So I have paid attention to the gate effect of molecularly imprinted polymers as a principle of new biosensing. I have succeeded in sensing of amino acids, glucose, alkaloids and anti-coagulant (heparin) using the gate effects. I believe that the gate effect is promising for actualization of monitoring many kinds of chemical signals for controlling artificial organs.

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23.

We have developed glucose oxidase (GOx)-based microelectrodes for glucose sensing with wide detectable range (0.01 – 20 mM). The modification of microelectrodes with PDMS and GOx layers allows to the detection of oxygen consumption by the enzyme reaction. Oxygen consumption by the enzyme reaction was detected cathodically by the microelectrode modified with permselective membrane for oxygen. The reduction current decreased with increasing the glucose concentration and reached at almost zero over 2.5 mM glucose. The sensing for glucose with high concentration regions was achieved with the oxygen regulation produced by the water electrolysis at another electrode which was positioned near the microelectrode. The current responses increased with increasing the oxygen concentration near the enzyme electrode. Detection range was improved and found to be up to 20 mM. Our approach will improve detectable range to higher concentration of glucose.

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24.

In order to improve the stability of Pt thin film electrode prepared on the surface of polyethylene terephthalate (PET) film, three types of binder, Nafion, polyethylene imine (PEI) and silica formed from perhydropolysilazane (PHPZ), were introduced on the surface of PET film prior to Pt sputtering. The strength and stability of obtained Pt-coated PET electrodes were evaluated by pencil scratch test and the observation of surface after 40℃ water immersion test. By the use of Nafion and PEI, both pencil scratch hardness and stability in water improved compared with that without the binder, while silica did not perform as a useful binder. Glucose oxidase (GOx) was immobilized on the surface of Pt-coated PET electrodes using electrodeposition and electropolymerization technique and their glucose sensor properties were examined. Glucose sensors prepared using Nafion and PEI as binder provided good response to glucose while the background current were somewhat high. Althoug! h the glucose sensor prepared using Nafion as binder showed poor response after 20 days of use, the sensor with PEI binder provided clear glucose response with lowered background current.

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25.

A novel immobilization method of enzymes with use of carbon fibers was tested. Ascorbate oxidase from cucumber was applied to immobilization onto the fibers and its performance characteristics as the enzyme sensor were investigated.

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26.

Carbon nanotube (CNT) showed the attractive properties for biosensor application, however, heterogeneity of as-synthesized CNTs was still limitation in order to get the designate and excellent characteristics. For example, about one-third of all possible single-walled CNTs exhibit metallic properties and the remaining two-thirds act as semiconductors. Recently, as-synthesized CNTs were sorted by metallic and semiconducting, using the technique of density-gradient ultracentrifugation. We report an amperometric biosensor based on the metallic CNTs. The configuration of the sensor was a nanocomposite of CNTs, glucose oxidase (GOx), and a nano-thin plasma-polymerized film (PPF). A mixture of the GOx and a CNT film is sandwiched with 6-nm-thick acetonitrile PPFs. It showed the more than excellent sensor performance than that with semiconducting CNTs.

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27.

In this study, we investigated the use of lysine oxidase (LO) immobilized on the gate of field effect transistor (FET) for the detection of L-lysine (L-Lys). LO was covalently attached to the SiO₂ gate modified with self-assembled monolayer of 3-aminopropyltrimethoxysilane (APS) through cross-linking by glutaraldehyde. LO catalyses the oxidation of L-Lys to 2-keto-6-aminohexanoate, NH₃, and H₂O₂, in which the production of NH₃ is expected to bring about an FET response by change in pH. Influence of solution pH on response for L-Lys was studied, and an optimal pH was determined to be 8.0. At pH 8.0, the response of LO-immobilized FET showed a linear dependence on the logarithm of concentration of L-Lys at the range from 1 μM to 100 μM with a slope of 1.8 mV/decade.

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28.

We have developed a new carbon film electrode material with thornlike surface nanostructures to realize efficient direct electron transfer（DET）with enzymes, which is very important for various enzyme biosensors. The nanostructures were fabricated using UV/ozone treatment without a mask, and the obtained nanostructures were typically 2-3.5nm high as confirmed by AFM measurements. XPS and TEM results revealed that these nanostructures could be formed by employing significantly different etching rates depending on nanometer-order differences in the local sp³ content of the nanocarbon film, which we fabricated with the electron cyclotron resonance sputtering method. With physically adsorbed bilirubin oxidase on the nanostructured carbon surface, the DET catalytic current amplification was 30 times greater than that obtained with the original carbon film with a flat surface. This efficient DET of an enzyme could not be achieved by changing the hydrophilicity of the flat carbon surface, suggesting that DET was accelerated by the formation of nanostructures with a hydrophilic surface.

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29.

Phenylalanine (Phe) and branched chain amino acids (BCAA) consisting of valine, leucine, isoleucine are important essential amino acids and have been currently noted as　biomarkers of phenylketouria or maple syrup urine disease. Blood amino acids are usually detected by HPLC analysis or enzymatic analysis, but they are still not rapid. We have previously shown that pre-electrolysis for 60sec with automatic monitoring system for sample fill-up was very useful to decrease the interference current from ascorbic acid and to measure precise enzyme-catalytic oxidation current for Phe with the Phe sensor using PheDH and DI (Chemical Sensors, Suppl. A, 58-60, 2011). This sensor might be applicable to monitor Phe in blood samples. In this study, we directed the next target toward practically available BCAA sensor that could eliminate the interference from ascorbic acid by applying pre-electrolysis using the automatic monitoring system.

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30.

Myoglobin (Mb) was adsorbed on a carbon-felt (CF) surface, and the resulting Mb-adsorbed CF (Mb-CF) showed a large cathodic wave in the potential range from 0 to －0.45 V vs. Ag/AgCl at pH 5.0 in the presence of dissolved O₂, based on the bioelectrocatalytic activity for the reduction of O₂. Ferrous-Mb [Mb-Fe(II)], which is electrochemically generated from met-Mb [Mb-Fe(III)], reacts with O₂, and the produced oxy-Mb [Mb-Fe(II)-O₂)] was electrochemically reduced back to ferrous-Mb: during this catalytic scheme, O₂ is reduced to H₂O₂. This bioelectrocatalytic activity of the adsorbed Mb was reversibly inhibited by cyanide, which binds to the heme-iron of Mb. When the Mb-CF was used as a flow-through bioelectrocatalytic detector at applied potential of －0.2 V vs. Ag/AgCl, the steady-state background current, due to the Mb-catalyzed reduction of dissolved O₂ in carrier, was reversibly changed by the injection of cyanide, resulting in peak-shape current responses. The magnitude of the inhibition peak current linearly increased with increasing concentrations of cyanide (from 0.5 to 3 μM). Apparent inhibition constant K^'_i was estimated to be 9.12 μM.

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31.

Silver thin film has good SPR characteristics, but it is unstable in buffered saline. Silver-bismuth (Ag-Bi) alloy shows good stability to halide ions. In this study, Ag-Bi alloy thin film was first applied to SPR measurement. By using Ag-1%Bi alloy film as sensor film, a good SPR curve was obtained and SPR sensitivity was approximately the same as silver or gold film. The sharpness of SPR image for 8.5μm i.d. microwell array obtained with Ag-1%Bi film was much higher than conventional gold film. Ag-1%Bi alloy film was stable in saline. SPR signal showed no changes for over two hours even in saline. By using indium tin oxide as an adhesive layer, Ag-1%Bi alloy film showed strong adhesion to glass substrate. Protein immobilization onto Ag-Bi alloy film was also possible via dithiobis (succinimidyl propionate).

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32.

Gold and silver are common metals for the SPR sensor chip, but their thin films show weak adhesion to a glass substrate. Therefore titanium or chromium are often used for an adhesive layer. We found that indium tin oxide (ITO) was good adhesive layer between silver-bismuth alloy film and a glass substrate. In this study, ITO film was used as an adhesive layer between gold (or silver) thin film and a glass substrate, and SPR characteristics were investigated. As for SPR curves and sensitivity, Au-ITO film showed similar results to conventional Au-Ti film. But the sharpness of SPR image for 8.5μm i.d. microwell array obtained with Au-ITO film was much higher than that obtained with Au-Ti film. ITO layer showed much stronger adhesion between gold (or silver) thin film and a glass substrate comparing with titanium or chromium. As an application, the sharper SPR image for a single lymphocyte could be obtained by the use of ITO as an adhesive layer.

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33.

In this study, we fabricated a flow-though measurement cell which can be easily installed and uninstalled to the CCD pH image sensor previously reported [1]. The flow-though sensor with a Ag/AgCl reference electrode functionalized also as the drain tube allowed examining a time-response property of the CCD pH image sensor. Unless using the cell, it had been difficult to exchange analyte solutions instantly without a break, so that a reference electrode had interfered with the time-response measurement. The successful time-response examination indicated that the pH response of each sensing pixel was almost completed within 0.2 s which was the readout time limited by the CCD operation. In addition, using a syringe pump and an injection valve, a flow-through measurement system also was developed. The flow-though measurement system continuously monitored a change of pH in the analyte solution, and visualized such the conditions as a movie.

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34.

In this study, a fast chemical imaging sensor system was developed and applied to fast imaging of chemical and enzyme reactions. The chemical imaging sensor, which is based on light-addressable potentiometric sensor (LAPS) is capable of visualizing the ion distribution on the sensor surface. The need of mechanical movement, however, has limited the speed of the conventional chemical imaging sensor system. In the developed system, the mechanical scan was replaced by a 8 x 8 LED matrix array. LEDs on a line of the LED matrix were modulated by the oscillator array which consisted of eight phase locked loop circuits. By switching the line of the LED matrix, fast chemical imaging at 10 fps was achieved.

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35.

A cobalt-iron alloy thin-film electrode-based electrochemical hydrogen-phosphate-ion sensor was prepared by electrodepositing an aqueous solution of metal-salts. The use of a cobalt-iron alloy electrode greatly improved the hydrogen-ion sensor response performance, i.e., the sensor worked stably for more than 7 weeks and showed a quick response time of several seconds. The Co₅₈Fe₄₂ thin-film electrode showed a linear potentiometric response to hydrogen-phosphate ion at the concentration range between 1.0 × 10⁻⁵ and 1.0 × 10⁻² M with the slope of -43mV/decade at pH 5.0 and at 30℃. A sensing mechanism of the Co-based potentiometric hydrogen-phosphate ion sensor was proposed on the basis of results of instrumental analysis.

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36.

To develop high performance nitrate ion-selective field-effect transistors (ISFETs) to detect a human salivary nitrate, we have investigated sensing materials and also polymer membrane materials. We prepared highly sensitive and selective prototype of FET NO₃^- checkers based on NO₃^--ISFETs using the suitable copper(I) complex as a nitrate-sensing material, 2-nitrophenyldodecylether (NPDDE) as a liquid membrane material (plasticizer) and poly(vinyl chloride) (PVC) as a conventional membrane material using the commercialized FET pH checker. We studied the sensor characteristics of prototype of FET NO₃^- checkers in detail. FET NO₃^- checkers showed linear characteristics from 10^-5.5 M to 10^-0.5 M with a response time of less than a few seconds. FET NO₃^- checkers also showed almost identical with the corresponding ion-selective electrodes as expected. FET NO₃^- checkers showed specific NO₃^- selectivity against coexisting major Cl^- in human saliva. So, we challenged to apply human saliva without pretreatment using direct potentiometry. Though we have only 10 human samples, we obtained relatively good correlation with the advanced ion chromatography.

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37.

A microfluidic device for the measurement of the K value was developed for on-site freshness check of raw fish. The K value calculated from the concentrations of the products in the degradation process of ATP is an effective indicator for fish freshness. The concentrations were measured using four enzymes and two pairs of three-electrode systems. Solutions were handled in the form of liquid plugs formed in a network of flow channels. To simplify structure and procedure for handling the plugs, hydrophobic and hydrophilic patterns were formed at the bottom of the flow channel and a wider portion were formed at a part of the flow channel to prepare plugs of predetermined lengths and merge plugs, respectively. Bypasses for air were formed in the flow channel to split plugs at predetermined positions. The plugs were ejected from each of reservoirs, split at the first sensing area, merged at the wider portion, and transported to another sensing area located in the lower stream. The current observed with solutions of different Inosine concentrations showed distinctly different values.

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38.

Coulometric detection of an analyte in a solution of the nL order was conducted by using redox reactions on a platinum electrode. The analyte was oxidized on the electrode on the electrode, whereas silver was deposited simultaneously on the other part of the electrode in another flow channel. Coulometric detection of the deposited silver showed a step change of generated charge. As a result, the value of the charge could be measured within 2 s, which is a marked contrast to the conventional methods which took more than 60 s to achieve the same sensitivity. The small background could also lower the detection limit. The lower detection limit achieved with this device and method was 49 (3σ). The device could also be used for biosensing of various substrates of oxidases.

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39.

We have recently developed a single digitated micro-electrode for microchip analytical systems using polystyrene as a substrate. Polymers offer cheap and easy to fabricate devices, however, polymer substrate has a rather rough surface, compared with glass substrate. The surface roughness of polymer substrates suggested that it possibly affects the electrochemical properties of metal-deposited electrodes on polymer substrates, such as sensitivity. We therefore studied surface roughness and response characteristic of Au- and Au/Ti-electrodes fabricated on polystyrene and pyrex glass substrates, respectively, employing AFM and continuous flow analysis. The AFM images showed that the electrode surface on the polystyrene substrate had the same roughness as on the glass although the surface of the polystyrene was rougher than that of the glass. In addition, current measurement was performed at various concentrations of ferrocyanide using a flow-through cell device with the electrodes fabricated on the two substrates. The results showed the same sensitivity and noise level for the two electrodes. In this study, we also studied the size, geometry, and arrangement of electrodes including the single digitated electrode as well as counter and reference electrodes fabricated on the polystyrene substrate for further improvement of the sensitivity in microchip analysis.

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40.

In microscopic analysis, the throughput is limited by the field of view magnified by an objective lens. Especially to measure precise cell concentration, suspension containing target cells in appropriate density range is required. Therefore,　counting cells in low density or in limited volume precisely is difficult for conventional microscopy. Toward high-throughput cell profiling, 2D photosensor-based analysis of cell populations has been proposed. Furthermore, it has been presented that a cell microarray technique, "microcavity array", enables cell entrapment with high efficiency. In this study, the 2D photosensor was integrated with microcavity array. Cell introduction, entrapment and detection were demonstrated in the integrated device. In this format, cell counting in wide dynamic range of 1 ~ 10⁴ cells was successfully performed. It will provide a novel platform to count and analyze cells in low density or in limited volume.

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41.

Photo-exited current can be generated through a molecular interface between a photo-excited molecules and a semi-conductive electrode in appropriate physical structure. Photo-excited current is totally dependent on the interfacial energy reaction which may fluctuated interfacial (molecule/semi-conduction) environment. The authors have developed site-specific electrochemical molecular immobilization method "EC tag method" for a preparation of ordered molecular layer on any of electro conductive material surface. Taking advantages of the EC tag method, synthesized sensor molecules were immobilized on a semi-conductor; fluorine doped tin oxide (FTO) surface. Output current can be obtained from the sensor molecule immobilized FTO when it was irradiated with laser light. The photo-excited current was clearly decreased when a ligand molecules were co-exist which was specifically bound to the affinity region of sensor molecule on FTO. The reason of the current decreasing is based on a occurring of steric hindrance by bound ligands which inhibit current transduction from photo-excited region to the FTO. The sensor can perform prompt and high sensitive affinity assay.

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42.

G-protein coupled receptors (GPCRs), which can recognize various extracellular compounds, including hormones, neurotransmitters and chemical molecules, represent the largest superfamily of cell surface receptors. Moreover, it was estimated that the 25 % of the 100 top-selling drugs targeted GPCRs. For these reasons, it is desirable to develop a robust, reliable, and cost-effective functional screening technique for compounds related to the GPCR in pharmaceutical industry. We have developed a new platform to detect chemical compounds binding to a GPCR by using a chimera G-protein which could transmit the signal from the G_s/olf-coupled GPCRs to the inward rectifier potassium channels (Kir 3). To improve the receptor profile, chimera G-proteins were designed by swapping C-terminal domain of G_αi protein to corresponding amino acids of G_αs or G_αolf protein. For evaluation of signal transduction from GPCR to ion channel, the chimera G-protein was heterogeneously expressed in HEK-293T cells with mutated potassium channel (Kir 3.1 (F137S)) and β1 adrenergic receptor. By utilizing of the chimera G-protein dramatically change of inwardly rectifying K⁺ current was occurred in the presence of β1 agonist (30 nM isoproterenol). Thus, this new sensing platform based on a chimera G-protein might provide a powerful method oｆ screen drug compounds targeting for GPCR.

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43.

An autonomous drug release system based on chemo-mechanical energy conversion was fabricated and tested. The system consists of two elements: pressure-reduction unit so-called "organic engine" and drug-release unit. Glucose oxidase (GOD) immobilized membrane was utilized in "Organic engine" for converting chemical energy of the glucose to pressure changes by the oxygen consumption in the GOD catalysis. The resulting pressure changes of the pressure-reduction unit showed sufficient relationship with the glucose concentrations. Afterward, the drug release unit which utilizes the output pressure change of the pressure-reduction unit was fabricated and evaluated by recording its release actions. The system was then fabricated by combining the both units. As a result of the evaluation test, the system showed the feasibility of autonomous glucose control in closed loop feedback setting as a natural pattern of the insulin secretion on feedback of blood sugar levels.

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44.

Change of local refractive index on the sensor chip surface is sensitively observed by using two-dimensional surface plasmon resonance (2D-SPR) sensor. Therefore 2D-SPR sensor has been applied to multi-sensor arrays which detect simultaneously a lot of antibody-antigen binding reactions and DNA-DNA hybridization reactions etc. On the other hand, we have successfully applied the 2D-SPR sensor to observe the response of individual mammalian cells adhered on a sensor chip without any probe reagents. We consider that the translocation of activated PKC to cell membrane adhered on a gold chip is observed by refractive index change. In this study, we tried to observe the response of rat pituitary GH3 cells for thyrotropin-releasing hormone (TRH) simulation by using 2D-SPR sensor.

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