Vol. 28, Supplement A (2012)

1.

We report on an amperometric biosensor that is based on carbon nanotubes (CNT) and plasma-polymerized film (PPF) for lower potential detection. The CNTs were sandwiched with 2 nm-thick acetonitrile PPFs. Under PPF layer was deposited onto sputtered gold electrode. We examined the three kinds of electron transfer mediator, Dimethylaminomethlferrocene (DMAMFc), Iron(III) ferrocyanide (Prussian blue; PB), Pottasium ferricyanide (Prussian red; PR). The electron transfer mediator was positioned between under PPF layer and CNT layer. It plays an important roles for lower potential detection; the polarized potential vs Ag/AgCl was reduced from +0.6V down to +0.4V. In those mediators, the DMAMFc showed the most valuable property. It is probably attributed to the good affinity between enzyme and DMAMFc for effective electron transportation. We also optimized the CNT and electron transfer mediator concentration for casting formation onto the under PPF layer. This high performance is attributed that CNTs offer excellent electrocatalytic activity and enhance electron transfer.

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2.

Freshness is an important factor that determines the quality of rice. In this study, we have developed an electrochemical microdevice that can measure the freshness of rice based on the measurement of the activity of peroxidase. In the existence of hydrogen peroxide and hydroquinone, the enzymatic reaction produced benzoquinone, which was reduced on a gold working electrode electrochemically and generated current was detected. The measurement on the chip showed larger currents with fresh rice, suggesting the accumulation of benzoquinone in the solution. The observed current clearly reflected harvest years and the condition of storage. The same tendency was observed by other conventional methods. The results demonstrated that on-site rapid measurement of freshness of rice can actually be carried out using our device.

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3.

We have previously developed the electrochemical enzyme sensors for several amino acids with our originally designed gold electrode chip on which amino acid dehydrogenase　and diaphorase are co-immobilized, and the automatic measurement system using pre-electrolysis. For example, developed Leu sensor system was successfully detected only branched chain amino acids by elimination of the interference from ascorbic acid (Chemical Sensors, Suppl. B, 95-97, 2011). Detection range of this Leu sensor was from 50 to 400 M. In this study, The Leu sensor was applied to measure Leu concentration in human blood plasma (HBP). However, Leu concentration in HBP, which was calculated from the calibration curve with PBS as a medium was significantly lower than expected value from HPLC analysis. Therefore new calibration curve for the Leu sensor was made with HBP as a medium on a trial basis.

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4.

　Use of carbon fibers as supports for immobilizing enzymes was investigated. Ascorbate oxidase was applied to immobilization onto the fibers chemically modified and their characteristics as the enzyme sensor were tested.

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5.

We report an amperometric NADH sensor based on the semiconductor-related CNTs. Although carbon nanotube (CNT) showed the attractive properties for biosensor application, 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. The configuration of the sensor was a nanocomposite of CNTs and a nano-thin plasma-polymerized film (PPF). A CNT film is sandwiched with 15-nm-thick acetonitrile PPFs. Under PPF layer was deposited onto a sputtered gold electrode. It showed the more than excellent sensor performance than that with metallic CNTs.

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6.

The wavelet transformation (WT) has been shown a powerful tool for the deconvolution of the electrochemical signals. The WT can decompose a signal as a function of the frequency in time domain. In the present study, the authors applied the WT to the amperometric response of a lactose biosensor to eliminate the interfering substance such as ascorbic acid. A power spectum density (PSD) signal related to the response of lactose was detected in low frequency range around 0.125 Hz. On the contrary, the PSD signal related to the response of ascorbic acid was detected in high frequency range around 0.05 Hz. The concentrations of lactose and ascorbic acid in the sample solution were estimated separately by the WT since the time constants of lactose and ascorbic acid of the biosensor are considerably different.

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清山賞受賞講演1

Biosensors are devices that use a biological reaction for detecting target analytes by generating a quantifiable electronic signal. They are powerful tools used in medical diagnostics, food quality control, and environmental monitoring. A typical biosensor is an integrated product incorporating biological elements and transducers. It has been consistently shown that dry process, plasma-polymerized thin films (PPFs), have potential for use as the interface between the two components of biosensors. To date, transducers have been amenable to miniaturization, and the concept of biochips has concomitantly expanded to encompass interdisciplinary fields such as microchips, arrayed sensors, nanotechnology, chemistry, and materials science. The roles and advantages of plasma-polymerized films in biochip design are highlighted. The main issues are that (i) plasma-polymerized films play an important role in the control and manipulation of biological components on the spatial region (patterning formation) of biochip surfaces while retaining their activity, and (ii) dry-process-based plasma-polymerized films are compatible and continuous with whole biochip processes.

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特別講演1

Microfluidic paper-based analytical devices, generally referred to as µPADs, are recently drawing attention as low-cost and simple to use alternatives of conventional microfluidic analytical systems (e.g. µTAS). The fact that µPADs do not require external pumping and high-tech signal detection systems makes them applicable to low infrastructure settings, such as they are for example encountered in the developing world, in field use or in home healthcare settings. Our group has been able to demonstrate that piezo inkjet printing is a useful method for both the microfluidic patterning of paper substrates and for the deposition of reagents required for (bio)chemical sensing onto the microfluidic system. In our first approach, an inkjet printing device has been used to fabricate three-dimensional hydrophilic microfluidic patterns on filter paper by inkjet etching. These patterned substrates have been used to realize inkjet printed quantitative chemical assays (glucose, pH and total protein in model urine) and lateral-flow immunoassays. Furthermore, the development of polymer nanoparticle-based "chemical sensing inks" has lead to improved quantitative performance of our µPADs. More recently, we have developed an environmentally friendly hydrophobic UV curable acrylate ink composition made of non-volatile and non-flammable compounds. With this ink composition, high-resolution microfluidic structures can now be patterned within less than 5 minutes on the surface of untreated filter paper. What makes inkjet printing technology so attractive is the fact that it is so far the only method allowing fabricating entire µPADs on a single standard manufacturing device, in some cases a device as simple as an off-the-shelf office inkjet printer.

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7.

Electrochemical determination systems of DNA sequence have been developed by a simple electrochemical deposition of chloro-2,2':6',2''-terpyridine platinum (II) chloride dihydrate on a glassy carbon electrode without immobilization steps on solid substrate. The intercalation of platinum complexes with dsDNA, which is formed with the complementary recognition of probe DNA to target DNA, caused to suppress the electroreduction of platinum complexes due to the steric hindrance and decrease of the diffusion coefficient. Thus, the catalytic current for reducing proton by the platinum deposited on the glassy carbon electrode decreased with the increase of the concentration of target DNA. An amplified response for measuring the current for reducing proton as compared with that for reducing platinum complexes itself could provide the highly sensitive measurement of dsDNA.

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8.

Cytosine methylation in DNA was determined by an enzyme linked immunosorbent assay (ELISA) with electrogenerated chemiluminescence (ECL) detection and employed for the DNA methylation assay of a long and real genomic sample for the first time. The developed method employed an anti-methyl cytosine antibody labeled with acetylcholinesterase, which was added to recognize single methylated cytosine in a DNA oligomer. The acetylcholinesterase converted acetylthiocholine (substrate) to thiocholine (product), which was accumulated on a gold electrode surface via gold-thiol binding. This surface accumulated pre-concentration made it possible to observe bright and distinctive ECL by applying a potential to the gold electrode in the presence of a tris(2,2-bipyridyl)ruthenium complex luminophore when the analyte DNA contained a methylation region. Methyl-cytosine was measured quantitatively in the 1 to 100 pmol range, which exhibits sufficiently high sensitivity to achieve real DNA measurements without amplification by a polymerase chain reaction. The proposed ECL method also exhibited high selectivity for methyl-cytosine against non-methylated cytosine, guanine, thymine and adenine nucleotides. Finally, original and methylated DNA samples were clearly distinguished with our method using a real DNA bacteriophage sample (48502 base pairs).

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9.

We have developed highly sensitive electrochemical sensors for endotoxin, potentially toxic compounds inducing septic shock. The endotoxin activates reactions of zymogens contained in the Limulus amebocyte lysate (LAL).　In this study, we used Boc-Leu-Gly-Arg-p-aminophenol (LGR-pAP) as a substrate for the last step of the LAL cascade reaction. To detect a released pAP (signal molecule) with high sensitivities, substitutional stripping voltammetry was employed. We fabricated a chip consisting of two cells: a sample cell containing mixture of 50 L of endotoxin solution and 50 μL LAL regents with 1 mM LGR-pAP, and a stripping cell containing 70 μL of 10 mM AgNO₃. A liquid junction was set between the cells to construct a battery cell like circuit. By connecting the electrodes in the cells, Ag⁺ in the stripping cell was reduced to Ag to be deposited on the electrode only in the presence of endotoxin in the sample cell. By quantifying the deposited Ag by anode stripping, we could detect as low as 0.1 endotoxin units (EU) L⁻¹ within 2 h.

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10.

It is proposed the novel agonist assay for nuclear receptor (NR) using functional peptide modified gold nanoparticles (GNPs: 15nm). GNPs have unique optical property that spectra of GNPs can change drastically depending on close to each other. This screening system employs functionalized GNPs whose surface were modified with 12 amino acid peptide in sequence of co-activator within nuclear system. Due to the affinity of the peptide, the functionalized GNPs are aggregated faster when nuclear receptor and agonist ligand are co-existed. This agonist screening system can recognize improper ligand(s) through simple method in 30 min. It can be systemized as high through-put screening (HTS) with good reproducibility. It is also possible to expand this system for the other NR. Moreover, it is expected that the method can estimate the force of agonist activity to NR and determine quantity of agonist ligand.

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11.

Observation of three-dimensional (3D) morphology changes of a single mammalian cell is very useful to understand cell response for various stimuli. Conventional techniques to evaluate morphology changes with sufficient precision and high temporal resolution are limited. Recently, a novel imaging method based on digital holographic microscopy (DHM) was developed for non-labeling microscopic observation of three-dimensional morphology. In this study, DHM was applied to monitor three-dimensional morphology change of individual PC12 cell, a nerve model cell, subjected to high K⁺ stimulation. Phase images of the rapidly swelling cell were acquired and time-lapse reconstruction of 3D cell morphology was performed from phase images.

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12.

We have previously reported to have developed an electrophysiological biosensor for detecting chemical compounds binding to a GPCR by using a chimera G-protein and the inward rectifier potassium channels (Kir 3). The chimera G-protein has determined the performance of this sensor. To improve the sensor output current, thirteen types of mutated G-proteins were designed by swapping C-terminal domain of Gαi protein to corresponding amino acids of Gαolf protein. For evaluation of signal transduction from GPCR to ion channel, the mutated 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 mutated G-protein dramatically change of inwardly rectifying K⁺ current was occurred in the presence of β1 agonist (30 nM isoproterenol). As a result, the sensor output current increased 1.5 times by using a new chimera G-protein (Gi/olf94) than reported previously c! himera G-protein (Gi/olfC-ter)

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13.

We studied on a method of blood coagulation test by using surface plasmon resonance(SPR). We have already reported that SPR measurement method allows us to measure flow velocity near the bottom face of a microchannel. Microchannels with inlet and outlet were fabricated using polydimethyl siloxane (PDMS). First, coagulation trigger regent was introduced into the microchannel, and then standard human plasma was dropped in the inlet. The plasma was introduced into the microchannel by a surface tension driven pump. After the introduction of the plasma, it was mixed with the coagulation trigger regent at an interface between the plasma and the trigger regent. We succeeded in measurement of flow velocity of the interface in the microchannels whose height were less than 100 μm(width:1.0mm, length: 10 mm). And, we also confirmed that the flow velocity correlates with the coagulation activity of plasma.

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14.

We have developed a disposable and user-friendly microfluidic device that could be used to estimate an appropriate antibiotic and its minimum inhibitory concentration. In this device, a microbial suspension solution was introduced into multiple chambers simultaneously with a very simple procedure. Microbes (Escherichia coli, K-12) introduced into the chambers were exposed to various concentrations of antibiotics (gentamicin) and their growth was quantified using a non-invasive and three-dimensional visualization technique. The length of time required for the determination of the minimum inhibitory concentration was only 12 h after cell seeding.

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15.

A microfluidic device for electrochemical determination of the activity of ATPase, which catalyzes the hydrolysis of ATP into ADP, was fabricated. In a series of enzymatic reactions, one of the final reaction products, hydrogen peroxide (H₂O₂), was used as an indicator for the ATPase activity and was detected by coulometry. Intermediates, pyruvate and ADP, were detected and linear relationships were observed between the output charge and their concentration, which indicated smooth enzymatic conversion by the experimental protocol. The obtained activity of sample ATPase (GroEL) was consistent with that measured by a conventional spectrophotometric method, which indicated that a highly sensitive measurement of ATPase activity in a sample of a small volume (294 nL) could be achieved using the electrochemical microdevice.

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16.

In this study, we have developed a local redox cycling-based electrochemical chip device for high-throughput cell analyses. In the device, two arrays of band microelectrodes were arranged orthogonally to fabricate a 256 (n²) array of crossing points with only 32 (2n) connector pads for external connection. The crossing points can be used as individual sensors by setting potentials at the column and row electrodes to appropriate values. For detection of the secreted proteins from single cells, the cells were trapped into the microwells on the chip device and cultured to immobilize the secreted proteins. After the cells were removed from the microwells, the immobilized proteins were electrochemically detected. The electrochemical images show that the secreted proteins from the single cells were successfully detected, which indicates that the chip device can be used as high-throughput single cell analyses, such as cell screening, reporter gene assay. We believe that the chip device can provide high-throughput electrochemical assays on cell analysis.

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17.

Bisphenol A (BPA) is a major material of polycarbonate, which is used as a food container in our life and known as endocrine disruptor. Animal experiments should be performed to study the effect of BPA on life. To determine the intake of BPA with food in animals, we need a sensing system of BPA with a small amount of biological sample. We have developed a disk-shaped microfluidic device for ELISA with 32 microchannels and chambers. In order to establish a rapid and sensitive assay system of BPA in biological sample, anti BPA antibody was immobilized on micro beads and introduced into microchambers on the microchannels on the device, in this study. Competitive immunoassay was performed using HRP conjugated BPA with a small amount of sample solution with in 20 min.

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18.

Microchips with biological functions now are powerful tools for point-of-care testing. However, the microtechnical production of microchips is very sophisticated and quite expensive. Ink-jet printing technology has developed over recent years into a preferred method of dispensing liquid micro-droplets for the purpose of printing and microfabrication. Advantages offered by this approach include precise volumetric control of dispensed material, data-driven flexibility, low cost, high speed and low environmental impact. In this study, we fabricated multiple single immunoassay chip with the piezoelectric inkjet printing system for the deposition and fixation of the 1st antibody on the microchannel. The microchip determined serum procollagen type I C-peptide (PICP) of a biomarker for bone formation with accuracy, high sensitivity, time saving ability, and low consumption of sample.

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19.

To measure salivary NO metabolites in clinical study and human engineering study, we have investigated sensing materials and also original biocompatible polymer membrane materials for high performance nitrate ion-selective field-effect transistors (ISFETs).

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 a segmented poly(urethane-urea) (KP-13) as a bio-compatible polymer material using the commercialized FET pH checker. The FET NO₃^- checker showed linear characteristics from 10^-5.5 M to 10^-0.5 M with a response time of less than a few seconds.

The FET NO₃^- checker showed specific NO₃^- selectivity against coexisting major Cl^- in human saliva. So, we carried out preliminary application of whole human saliva on a ship handling simulator using direct potentiometry with several salivary sampling. We will report preliminary results of salivary sampling for the FET NO₃^- checker.

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20.

A novel flow-through polymerase chain reaction (PCR) microfluidic system using vapor pressure was developed that can achieve ultra-rapid, small volume, DNA amplification on a chip. The 40cycle amplification can be completed in as little as 120 s, making this device the fastest PCR system in the world. The chip device is made of a pressure sensitive polyolefin (PSP) film and cyclo-olefin polymer (COP) substrate which was processed by cutting work to fabricate the microchannel. The enclosed structure of the microchannel was fabricated solely by weighing the PSP film on the COP substrate, resulting in superior practical application. The vapor pressure in the denaturation zone of the destabilizing flow source was applied to the flow force, and ultra-rapid, efficient amplification was accomplished with a minimal amount of PCR reagents for detection. The flowing rhythm created by vapor pressure minimized the residual PCR products, leading to highly efficient amplification. For field test analysis, airborne dust was collected from a public place and tested for the presence of anthrax. The PCR chip had sufficient sensitivity for anthrax identification. The fastest time from aerosol sampling to detection was theoretically estimated as 8 min.

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21.

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 of bovine whole blood was performed with the grafted electrode. The anodic current was sensitive to the heparin. The result indicates that the electrode grafted with heparin-imprinted polymer can work as a reagentless sensor for heparin in blood.

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22.

We have successfully developed bacterial sensors based on molecularly imprinted polymers using overoxidized polypyrrole. The molecularly imprinted polymer was prepared by electrochemical overoxidation of polypyrrole, which had been doped with bacilli as a template. The sensor was fabricated on a gold-coated quartz microbalance sensor, and the results of dielectrophoretic QCM measurements demonstrated that the greatest responses resulted from template bacilli rebinding.

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23.

We have developed chemical sensors based on alkanethiol self-assembled monolayers. For fabricating the monolayer based sensor, intermixed monolayers consisting of the alkanethiol and cholesterol were formed on both amorphous and single crystal gold electrodes via the self-assembly precess, and the cholesterol was extracted to produce a slot for rebinding. In this report, the responses of the sensors thus assembled are discussed along with some basic characteristics, such as selectivity. Sensor systems developed based on this concept have been recently commercialized from JSK Co. Ltd, and are validated for food cholesterol quantification.

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24.

An amperometric gas sensor based on electrolysis of CO gas has been developed by using gas permeable membrane made of polytetrafluoroethylene (PTFE))modified by ion implantation technology. The ion implantations of several kinds of ion into PTFE membranes with fluenses of 1×10¹⁴ ～5×10¹⁵ ions/cm² was carried out to modify the gas permeable membranes. Gas permeable electrodes were prepared by Au coating on the ion-implanted PTFE membranes. For CO detection, sensors constructed with the ion-implanted gas permeable electrode showed 5.5～38 times higher sensitivity than that used non-ion-implanted one. The selectivity for organic vapor gas such as methanol and iso-propyl alcohol, was improved to more than twice compared with using Pt-Black electrode sensor. In the case of CO detection, the modification of membranes brings an active nature of electrode process of CO oxidation, which improves selectivity of CO. The surface modification of PTFE by ion implantation will be useful method for development of a practical CO gas sensor.

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25.

We obtained a very interesting result of a large electrode oxidation wave of hydrogen molecule appearing after the long-term electrode reduction of the aminated carbon felt electrode in sulphuric acid. The reversible redox waves between the hydrogen ion and the hydrogen molecule can be observed by the introduction of diazo and sulpho groups into the surface of the carbon felt electrode. The introduced diazo group must be stabilised by the introduction of a sulphonic acid group; because an ionic pair (or chemical bond) may form between the positive diazonium ion and the negative sulphonic acid ion. Moreover, we also found that the reduction wave of oxygen appears in the significantly positive potential region after the electrolytic introduction of a sulpho group. In these catalytic electrode reactions, it can be considered that the diazo group and the hydrazino group (or azo group) consist of the catalytic sites for the cell reactions.

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26.

Multielectrolytic modified carbon electrode (MEMCE) was fabricated by using the following electrolytic-oxidation/reduction processes. First, diazo group is introduced by the electrode oxidation of carbon felt electrode in an ammonium carbamate aqueous solution, and next, sulfonic acid group is introduced by the electrode reduction of diazotated carbon felt electrode in sulfuric acid. We found that the reversible redox waves between hydrogen ion and hydrogen molecule at highly positive potential range appear in the cyclic voltammogram obtained by using the MEMCE. A coulometric cell using MEMCE was constructed and was used for the measurement of dissolved hydrogen. The typical current vs. time curve was obtained by the repetitive measurement of the dissolved hydrogen. These curves indicate that the measurement of dissolved hydrogen is finished completely in a short time (~20 s). Hence the present coulometric method could be used for the measurement of the dissolved hydrogen concentration.

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27.

There are Highly-sensitive H₂O₂ detection devices need for bio-sensing devices. Also, industrial processes need the devices as control of H₂O₂ concentration. Metal phthalocyanines (MPc) are known as catalysts for oxygen reduction reaction, and can use as H₂O₂ detection materials. In this study, MPcs with various centered metal thin-film prepared by electrochemical deposition ITO electrodes. XRD patterns shows that unsubstituted MPcs (M=Co, Ni, Cu, Zn) thin films are α forms. The MPcs thin-films were composed with fibrous crystals and the morphologies were largely dependent on the centered metals in MPcs. Among the MPc electrode, only CoPc-ITO showed the potentiometric response for H₂O₂ concentration. On the other hand the fluoro-CoPc-ITO showed amperometric highly-sensing for H₂O₂.

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28.

Manganese oxides can reversibly insert/extract alkali cation, which can be utilized as electrodes for an ion-sensing. Additionally, polycation-containing manganese oxides can reversibly insert/extract anions into/from manganese dioxide inter layers by the electrochemical process. In this study, we examine poly(allylamine)-containing manganese oxides (PAAm-MnOx) for the sensing of chloride ions. The Pt/PAAm-MnOx electrodes show stable potential response to chloride ion in KCl aqueous solution. The PAAm-MnOx electrode, covered with chloride ion selective membrane (Pt/PAAm-MnOx/PVC), exhibits quick and Nernstian response to chloride ion activity, and better potential stability than the electrode without PAAm-MnOx (Pt/PVC). Chronopotentiometric mesurments and AC impedance analysis suggested that PAAm-MnOx as the inner layer effectively reduces the resistance of the all-solid-state electrode, and thus improves the stability for ion-sensing.

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29.

We developed a CCD-type calcium ion image sensor with plasticized poly(vinyl chloride) (PVC) membrane contained a calcium ionophore. The plasticized PVC membrane contained 4,6-Di-N-octadecylcarbamoyl-3-oxabutyryl-1,7,10,13,19-pentaoxa-4,16-diaza cyclohenicosane (K23E1) as Ca²⁺ ionophore was prepared by a solution casting method. The out-put signal of sensing pixels linearly increased with logarithmic concentration of calcium ion from 10^-5 M to 10^-2 M. The sensitivity of calcium ion was high, and the presence of sodium, potassium and magnesium ions little affected the sensor response. The membrane content and the response were comprehensively discussed with our previously reported CCD-type calcium ion image sensor with plasticized PVC membrane contained alkylphosphate exchanger. The CCD sodium ion image sensor displayed real-time images of calcium ion concentration, and can dynamically monitor instant changes of calcium ion concentration.

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30.

We have revealed that the facilitated ion transfer of metal cations, such as K⁺, Li⁺, and Ca²⁺, across the interface between plasticized PVC and water interface is electrochemically quasireversible. The heterogeneous rate constant (k⁰) is estimated in the range of 10^-2-10^-3 cm s^-1. The kinetic information is very important for sensor applications because the response time should depend on the kinetics. For the better understanding, we simulated the effect of kinetics on the hydrodynamic voltammetry. The kinetics affects on the shape of voltammogram. To reach the diffusion-limited steady state current of metal cation from water to PVC, more negative potential is applied. The slower kinetics decrease current response slightly for the flow injection analysis.

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31.

We have reported N₂ gas-diluted 1% hydrogen gas response properties for Pt-Ti-O gate Si-MISFET hydrogen gas sensors. We also reported a stability data of sensing amplitude for 9 repeated hydrogen expose every 7minitutes. The average sensing amplitude is 624.4 mV with standard deviation of 7.27mV.　The rising response time is so fast around 0.4s. The turning off properties of the sensor shows similar tailing like air-dilured hydrogen gas response. According to the logarithm-linear sensor characteristics of hydrogen concentration dependence, the accuracy of the measured hydrogen concentration will be less influenced by this tailing behavior. We also investigated the Pt-Ti-O gate Si-MISFETs as for oxygen gas sensors. The oxygen removing response of the FETs after N₂-gas expose show a long tail behavior which will be approximately described logarithmic linear function of time expected from Elovich (or Roginsky-Zeldovich) equation. The direction of Vth shift is identical to hydrogen gas expose, which is reverse change for the hitherto-developed Si-MIS type oxygen sensors

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32.

Diode-type gas sensors (Pd-Pt/TiO₂) have been fabricated with anodized TiO₂ films and Pd-Pt alloy electrodes and the improvement in the H₂ sensing properties of Pd-Pt/TiO₂ by polytetrafluoroethylene (PTFE) or polyvinyl alcohol (PVA) coating on their electrodes has been performed in this study. The H₂ response of all sensors in wet air was larger than that in dry air. The coating of relatively thin polymer films on the Pd-Pt electrodes was effective for improving the H₂ response of Pd-Pt/TiO₂, but the H₂ response tended to decrease with an increase in the thickness of the polymer films on the electrodes. In addition, O₂ concentration dependence of H₂ response of the sensor was not improved, but the humidity dependence was improved in some cases, by the polymer coating of the Pd-Pt electrodes.

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33.

Stabilized nanoparticles, composed of cross-linked Poly(N-isopropylacrylamide) (PNIPAM) with ethyleneglycol dimethacrylate (EGDMA), were prepared by precipitation polymerization via atom transfer radical polymerization (ATRP). The PNIPAM nanoparticles without crosslinking (P-PNIPAM) were soluble in water below the lower critical solution temperature (LCST) at 32ºC, however, PNIPAM nanoparticles cross-linked with 1.5 mol % EGDMA (SP-PNIPAM) were stable in water below LCST. SP-PNIPAMs were loaded on the quartz crystal and its HCl gas adsorption/desorption properties were investigated. Adsorption/desorption properties were affected by the SP-PNIPAM loads on the crystal. Especially the reversibility worsened and the response time lengthned with increasing the SP-PNIPAM loads, although the P-PNIPAM showed the fast and reversible response even at larger loads.

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34.

Multi-walled carbon nanotubes (MWCNTs) array with about 40 nm in diameter and 500 to 1300 nm in length was directly grown on the Au interdigitated electrodes by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD). The growth catalyst at the tip of MWCNTs array was clarified to be Ni/Ni₃C/MWCNT by transmission electron microscope (TEM) and selected area electron diffraction (SAED). The sensing properties of MWCNTs array to NO₂, H₂S, CH₃SH and C₈H₁₀ were investigated at operating temperature from 100 to 250°C. The resistance changes to sulfur gases were higher than those to NO₂sub and C₈subH₁₀. It was suggested that Ni at the tip was sulfidized to be NiS in sulfur gases and that the p-n junction was formed at the interface between p-type NiO and n-type NiS leading to selectivity to sulfur gases.

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35.

Last time we reported very fast response CO sensors. However we needed to increase response of the sensor to apply for industry. In this study, we prepared cerium oxide thick films which consisted of clustered grains prepared from core-shell cerium oxide / polymer hybrid nanoparticles as a raw material and investigated sensing properties of them. As a result, it is clarified that the response to CO gas of the cerium oxide thick film made from the core-shell nanoparticles are better than that of cerium oxide thick film made from nanoparticles prepared by precipitation. Furthermore, the response increased when Au nanoparticles are added on the surface of the cerium oxide thick films.

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36.

We have been developing a battery driven mini-bead type semiconductor CO sensor using a periodic heater ON/OFF operating method. In this report, we have focused on the mechanism of CO response at room temperature during the OFF period. Using a TPD-MS analysis, we have found that the CO response arose mainly from CO adsorption on Pd loaded SnO₂.

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37.

In the previous work, we reported that the oxygen adsorbs as an O^2- in extremely dry atmosphere over 350^oC. In this study, we aimed to confirm the oxygen adsorption species and sensing mechanism to the hydrogen in dry or wet atmosphere. They were investigated by the relationships between the electric resistance and oxygen partial pressure and between sensor response and hydrogen partial pressure. The obtained results indicated that the oxygen adsorbs as O^- and O^2- by the competitive adsorption below 350^oC in dry atmosphere. Additionally, in wet atmosphere, O^2- adsorption seems to be disturbed by H₂O adsorption which decreases the electric resistance, and thus the oxygen adsorbs as O^-. On the other hand, the sensor response to hydrogen in wet atmosphere was lower than that in dry atmosphere because the O^- adsorption species react with hydrogen after consuming the O^2- adsorption species.

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38.

Based on material designs of receptor function and utility factor, Pd-loaded SnO₂ cluster sols were prepared by hydrothermal treatment. A mixture of stannic acid gel (SnOH₄) and Pd(NO₂)₂(NH₃)₂ solution was hydrothermally treated at 200^oC for 3h at 10MPa. In the process, the pH control in hydrothermal treatment was important for controlling the cluster size. The suitable loading amount of Pd was 0.1 mol%, which was very lower than those of usual Pd-loaded SnO₂ prepared by impregnation method, meaning that the loaded Pd is dispersed finely on SnO₂ cluster. The obtained Pd-loaded SnO₂ cluster was deposited on alumina substrate with Au electrodes by spin coating method to fabricate thin film type sensors. The sensor of Pd-loaded SnO₂ cluster showed higher gas response compared with the devices fabricated from SnO₂ sols, SnO₂ cluster and Pd-loaded SnO₂ sols. Especially the response to toluene gas, large size gas molecule, was enhanced by introducing designs of receptor function and utility factor.

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清山賞受賞講演2

The fundamental sensing mechanism of tin oxide semiconductor gas sensors put to practical use for gas alarms was revealed by the model to clarify the electrical conduction mechanism and the reaction mechanism on the tin oxide surface. By utilizing of this knowledge, we have developed a highly selective methane sensor based on the highly sensitive tin oxide thin film with nano-columnar structure and a selective catalyst layer. By combining the MEMS technology with highly selective methane sensors, ultrashort pulse driving become possible, and a battery-powered micro methane sensor has been developed.

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特別講演2

An odor sensing system using multiple sensors with different characteristics and pattern recognition technique has been studied. Here we focus on the sensing system robust against environmental changes such as concentration, temperature and humidity. We introduced short-time Fourier Transform for preprocessing of sensor responses to odors with irregularly changing concentrations. It was found that short-time Fourier Transform was effective to extract the feature related to sensor-response speed. It was implemented into an odor recognition chip for real-time application. Moreover, the novel preconcentrator without adsorbent will be presented. Another topic is an olfactory display, smell-presentation device. The multi-component olfactory display, the exploration of odor components and its application to a new multimedia platform will be explained at the conference.

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39.

Solid electrolyte type carbon dioxide gas (CO₂) sensor operable at moderate temperature was fabricated by using trivalent aluminum cation conducting (Al_0.2Zr_0.8)_20/19Nb(PO₄)₃ solid electrolyte. The Nd₂O₂CO₃-(0.52Li₂CO₃-0.48Na₂CO₃) solid and Al metal thin film were selected as the auxiliary sensing electrode and reference electrode, respectively, to produce a sensor that exhibits superior sensing performance in terms of a quantitative, continuous and reproducible response with obeying the theoretical Nernst relationship at the temperature as low as 350°C. Since the sensor exhibited stable CO₂ gas detection over 2 months, it is expected to be a practical on-site CO₂ gas detecting tool.

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40.

The CO₂ sensor operative at room temperature was fabricated by applying a solid-state electrolyte (NASICON (Na₃Zr₂Si₂PO₁₂) or LISICON (LiTi₂(PO₄)₃)), ITO (indium tin oxide) and an auxiliary phase (Li₂CO₃-BaCO₃ (1:2 in molar ratio) or Li₂CO₃-In₂O₃ (4:1 in molar ratio)). Their CO₂ sensing properties and the cross sensitivities to NO₂ (2 – 7 ppm) were measured under 30 %RH (relative humidity) between 30 and 100 °C. The NO₂ cross sensitivities of the ITO-attached NASICON sensor with Li₂CO₃-BaCO₃ was estimated to be 29.0 mV at 30 ^oC. In contrast, the ITO-attached NASICON sensor with Li₂CO₃-In₂O₃ demonstrated fairly good CO₂ sensing properties and were not affected much by NO₂ coexisting in the atmosphere. The 90 % response time was within 10 min and the EMF values were proportional to the logarithm of CO₂ concentration. When the sensor was operated in the range of 250 – 2500 ppm CO₂ at 30 ^oC, the EMF (electromotive force) change was 30.4 mV. In addition, when the sensor operated in the range of 2 – 7 ppm NO₂ at 30 ^oC, the NO₂ cross sensitivity was estimated to be 3.7 mV.

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41.

A planar-type zirconia sensor having (Pt/YSZ)/YSZ/(Pt/YSZ) structure was fabricated, and one of the Pt/YSZ electrode was coated with MgAl₂O₄, Au, Au/YSZ powder. The EMF response of fabricated sensors to ethanol and toluene at sub-ppm levels was examined. The coating of the Pt/YSZ electrode with MgAl₂O₄, Au, Au/YSZ powder induced decreasing the oxide ion activity at triple phase boundary and increasing the EMF response. The response behavior depended on the thickness of the over coated layer and material. The use of the Au/YSZ working electrode instead of the Pt/YSZ working electrode resulted in the enhancement of the sensing response.

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42.

The toluene (C₇H₈) sensing behavior for a yttria-stabilized zirconia (YSZ)-based sensor utilizing a NiO sensing electrode (SE) was simulated with a computational model. The developed model considered the following simultaneous phenomenon: gas species diffusion within the microporous NiO electrode, adsorption, desorption and ionization of oxygen on NiO particles at high temperature, as well as the catalytic oxidation of toluene. The sensing signal was expressed with the Butler-Volmer equation, which was applied at the triple-phase boundary of the sensing electrode. Parameters for toluene sensitivity were fit to a mixed-potential sensing model to obtain the electromotive force (emf) of the YSZ-based sensor utilizing NiO-SE exposed to C₇H₈ at ppb levels. Good agreement was observed between simulated and experimental emf values within the concentration range of 50 to 300 ppb. This validated model will be used for future parametised studies.

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43.

Mixed potential ammonia sensors with Au electrode modified by various metal oxides were fabricated, and influences of these metal oxides on suppression effect of interference by C₃H₆ and H₂O were investigated. Also, stability of the metal oxides at high temperature and reactivity with YSZ were examined. As a result of model gas tests, sensors with Co₃O₄ added Au electrode showed favorable property; good gas selectivity and less interference by H₂O. From our experiments, it was suggested that interaction between H₂O and metal oxides was important factor affecting interference by H₂O

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44.

A yttria-stabilized zirconia (YSZ) based mixed-potential-type sensor utilizing SnO₂ (+ 30 wt.% YSZ)-SE has been fabricated, and was found to be capable of detecting H₂ sensitively at 550^oC. In order to enhance the selectivity towards H₂, a selective C₃H₆ oxidation catalyst was employed to minimize unwanted responses from interfering gases. Among the examined metal oxides, Cr₂O₃ demonstrated the capability to oxidize C₃H₆ selectively, with only minimal effect on H₂ sensing performance. Thus, the YSZ-based sensor using SnO₂ (+ 30 wt.% YSZ)-SE coated with a catalyst layer of Cr₂O₃ and Al₂O₃ intermediate layer was constructed and its sensing characteristics were examined. The sensor was found to be capable of generating a sensitive response toward H₂, with only minor responses toward HCs and NOx gases at an operating temperature of 550^oC under humid conditions (21 vol.% O₂ and 1.35 vol.% H₂O). The sensor had a linear response relationship when plotted against H₂ concentration within 20 - 800 ppm H₂ on a logarithmic scale, indicating that the sensing mechanism is in good agreement with mixed-potential theory.

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45.

A possible working mechanism for a Mn-based reference-electrode (RE) used in the yttria-stabilized zirconia (YSZ)-based gas sensors is proposed here. It was observed visually via EDX measurements that after calcination at high temperature, Mn ions diffused into YSZ, forming a solid-solution (Mn-YSZ) with the YSZ. Additionally, the response transients toward different concentrations of oxygen for the sensors comprised of Mn-based (or Mn-YSZ) sensing-electrode (SE) and Pt/air-RE was compared. The similar sensing behavior of these sensors indicates that the Mn-YSZ solid-solution is the primary cause of the gas insensitivity of the Mn-based-RE. Furthermore, it was confirmed that the content of Mn ions in the YSZ reached its solubility limit after calcination. Based on these results, we postulated that, due to the existence of the Mn ions in the YSZ, adjacent oxygen vacanciesⅤo^¨ may be trapped near the manganese ions at operational temperatures ≤550^oC, resulting in insensitivity towards not only O₂ but also to other various gases.

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46.

In our previous study, it was found that CO can be detected sensitively by difference of catalytic activity to CO oxidation. Sensing properties for CO in various gas atmospheres were studied by using 10wt%Au-In0.95Sn0.05O1.5 cathode, RuO₂-La_0.6Sr_0.4CoO₃ anode and La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ electrolyte. In this study, we studied the influence of coexisting gas on CO sensing property. Coexistence of H₂, CH₄ and CO₂ shows almost no influence on CO sensitivity, however, O₂ shows large influence on CO sensitivity. Effects of additives on cathode to O₂ coexistence influence were studied. It was found that addition of oxide to cathode affected the oxygen concentration dependence. In particular, addition of Ce(La,Pr)O₂ to cathode was the most effective for reducing of oxygen concentration dependence.

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