Vol. 34, Supplement A (2018)

17.

To develop on new stress-sensing devices for stress science study, we have investigated ISFET (ion-selective field-effect transistor) based biosensors for measurement of several salivary stress-marker candidates and also have studied organic semiconductor based ISFETs, OFET based biosensors. During the fundamental studies on the prototype of stress-sensing devices, such as electrophoretic microfluidics and ISFETs for real salivary samples of healthy volunteers, we found salivary nitrate will be a biomarker candidate on the autonomic nervous system response to stress. To make a scientific study on the acute stress response mechanism of salivary nitrate, we investigated simultaneous monitoring for healthy volunteers of a ship handling using wearable heart rate monitor and salivary nitrate sampling measurement by prototype of salivary nitrate checkers based on NO₃^--ISFETs using direct potentiometry. We will introduce the several results of acute stress subject-experiments for healthy volunteers from the point of view from the behavior of salivary nitrate for mental workload of events.

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18.

Flexible devices have many potential applications in wearable electronics, robotics, health monitoring, and more. Mechanically deformable devices and sensors such as flexible devices enable conformal coverage of electronic systems on curved and soft surfaces. Sensors utilizing liquids confined in soft templates as the sensing component present the ideal platform for such applications, as liquids are inherently more deformable than solids. Here we demonstrate microfluidic environmental sensors using liquid metal, highly sensitive pressure sensor based on tactile diaphragm pressure sensor, and temperature/humidity/oxygen sensors with mechanically robust liquid-liquid “heterojunction”. This report will present an important advancement towards the realization of liquid-state electronic systems

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To improve detection sensitivity of a microdevice based on coulometry coupled with metallization, a metal wire was used to connect two flow channels to cause redox reactions as an alternative to a liquid junction. Three methods were tested. First, a wire with Ag/AgCl on both ends was used. Next, to increase overpotential, one end of the wire was replaced with nickel or zinc. Alternatively, potential difference was applied directly to solutions in the flow channels. Each of these methods had an effect and the charge or the amount of silver deposited on the platinum electrode could be increased by increasing the potential difference between the solutions in the two flow channels. With the third method, the achieved lower detection limit for H₂O₂ was 2.4 nM (3σ).

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20.

Phosphorous is one of three major nutritional elements for plants and usually exists as phosphate in nature. For wastewater treatment, the development of a high-performance phosphate sensor would be very helpful. A novel phosphate ion-selective electrode was constructed using a molybdenum electrode coated by a molybdenum phosphate complex. The sensor exhibited a linear response to HPO₄^2- in a concentration range from 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ mol L^-1 with a slope of −29 mV dec^-1. The response was unaffected by common anions in nature, such as chloride, carbonate, and sulfate. The electrode was stable for at least 4 weeks.

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21.

In this research, we fabricated a screen-printed reference electrode using poly vinylidene di fluoride (PVdF) binder and silica gel. We newly prepared fine KCl particles of 15 m diameter, and changed component and preparing process of ink to improve a long-term stability of the reference electrode. The reference electrode indicated 2 minutes set-up time and 20 days lifetime. These performance were from the fine structure of liquid junction layer and electrolyte layer. Moreover, the inner structure of the reference electrode was analyzed by electrochemical impedance spectroscopy. Three semicircles and finite diffusion impedance appeared on the Nyquist plot. The parameters related to the lifetime and set-up time of the reference electrode were estimated by curve fitting using an equivalent circuit.

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22.

A reference electrode used for electrochemical measurement generally has a liquid junction to allow the ion transport between an internal electrolyte and a test liquid for electrical conduction between the reference electrode and the test liquid. However, the liquid junction often causes troubles such as clogging and test liquid contamination. Previously, we have developed a chip type device integrating a reference electrode without liquid junction using a close bipolar electrode system. In this research, we fabricated a probe type amperometric sensor integrated with liquid-junction free reference electrode system based on the knowledge obtained by the previous study. This compact device demonstrated to be used for ferrocenemethanol quantification. We also examined the apparent equation potential of the voltammogram. From this examination, we found the method expected to lead the improvement of the stability of the reference potential of the probe type device.

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23.

Hydrogen peroxide is one of products for many enzymatic- and electrochemical- reactions, then simple and highly selective detection methods for H₂O₂ are strongly required. As some metal complex catalysts have high selective catalytic properties and chemical stability, we focused on the metal phthalocyanines (MPc) and their family for electrode material of hydrogen peroxide sensor. In this study, various MPc thin-films were prepared on ITO electrode by electrochemical and drop-coating methods, and their potentiometric and amperometric detection properties to H₂O₂ were evaluated. Among the tested MPc based sensors, the CoPc thin-film electrode showed good potentiometric response from micro molar concentration revel. In these sensor responses, an electrochemical 2-electron H₂O₂ reduction reaction was proposed. As for the amperometric sensing, the cobalt naphthalocyanine and the cobalt hexadeca-fluoro phthalocyanine-based sensors showed high sensitive amperometric responses to H₂O₂.

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特別講演1

Electrochemical impedance spectroscopy (EIS) has been applied to evaluations of various electrochemical devices because time constants in electrode response can be discriminated by the measurement of transfer function in the wide frequency range. The application of EIS allows the information regarding electrode structure and electrochemical reaction mechanisms and enables highly sensitive detection of a sensor. In this presentation, the theory of EIS is introduced firstly. And some topics related to impedance analyses on electrochemical sensors are explained, for example, 1. Equivalent circuit and Faradaic impedance, 2. Impedance of porous structure, 3. Diffusion impedance of micro-electrode, 4. Sensing by resistmetry, 5. Corrosion sensor for infrastructure, and 6. 3D impedance to analyze battery electrode.

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特別講演2

This report describes three kinds of conductometric sensors using semiconductor thin-films. The first one is a sensor for detecting organic airborne particles such as pollen, mold spores, PM2.5 and house dust. The sensor is fabricated by MEMS technology. The sensing film is a multi-layered one composed of SnO₂-based and Fe₂O₃-based films. The sensor resistance changes toward these particles depending on their sizes and constituents. The kind of particles can be identified from its resistance change. The second one is a sensor made of WO₃-based multi-layered thin-films with interspaces. The sensor is selective and sensitive to H₂ gas. The Ag addition to the sensing film increases the sensitivity and selectivity to NO gas, while the deposition of Pt nanoparticles on the sensing film enhances the sensitivity to NH₃ gas. The third one is a sensor equipped with an adsorption/desorption layer made of activated carbon supported on a rotation mechanism. The sensor identifies isovaleric acid and ethanol gases from its resistance change.

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24.

A new catalytic combustion-type C₂H₄ gas sensor was fabricated by using Pt-loaded Ce_0.76Zr_0.19Zn_0.05O_1.95 (CZZn) solid solution as the C₂H₄ oxidizing catalyst. The sensor employing 10 wt.% Pt / CZZn catalyst responded to C₂H₄ gas smoothly and reproducibly with linear response to C₂H₄ gas concentration change at the temperature as low as 85 °C. The 50 % response time of the sensor at 85 °C was 2.0 s. The sensor also exhibited the high C₂H₄ selectivity without showing meaningful response to other VOCs. Furthermore, the present sensor was found to be able to detect C₂H₄ even in a wet atmosphere whose humidity was 90 %.

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25.

H₂-sensing properties of diode-type gas sensors using　an anodized TiO₂ film and Pt electrodes coated with or without Au have been investigated, and the effects of Au coating on the Pt electrodes on the H₂-sensing properties have been discussed in this study. The Au coating on the Pt electrode greatly improved the response to 8000 ppm H₂ in dry air, to reduce the O₂-concentration dependence of the H₂ response. On the other hand, the Au coating on the Pt electrode largely reduced the catalytic combustion behavior of H₂ over the Pt electrode in dry air. These results probably indicate that a decrease in the number of oxygen adsorbates on the electrode increased the number of dissociatively adsorbed and dissolved hydrogen species and then enhanced the H₂ response. In addition, the addition of moisture into the target gas improved the H₂ response in air, whereas it was ineffective in improving the H₂ response in N₂. They are probably because the water molecules adsorbed on the electrode surface interrupted the adsorption of oxygen molecules under the operation in air, leading to reduction of the H₂-oxidation activity on the electrode.

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26.

Oxygen adsorption state of Inn₂O₃ nanoparticles was investigated based on the depletion depth model. According to the relationship between oxygen partial pressure and the relative resistance, which is ratio of the electric resistance in atmosphere with and without oxygen (R/R0), it was found that the Inn₂O₃ nanoparticles are in the volume depletion state in dry and wet atmospheres. Additionally, oxygen adsorption equilibrium constants for O- and O²- were well related to the depletion depth (Rair/R0). The sensor responses to 8 ppm CO and H₂ are also strongly attributed to the depletion depth in the Inn₂O₃ nanoparticles.

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27.

In this study, Au nanoparticles were added on the ZnO nanoparticles using co-precipitation method to obtain the highly selective toluene sensor. Au loading amount was set at 0.15 mol%. Particle size of the Au nanoparticles on the ZnO was about 2 nm, and Au nanoparticles were highly dispersed. The sensor responses to 100 ppm ethanol, acetone, and toluene for ZnO NPs were 980, 1430, and 840, respectively, while those of Au-ZnO NPs were 7, 7, and 92, respectively. Such strong reduction on the sensor response seems to be caused by the catalytic oxidation on the surface of sensing films. Nevertheless, sensor response to toluene using Au-ZnO NPs was more than 10 times higher than those to ethanol and acetone. It is considered that catalytic activity as well as electronic sensitization gives high gas splitting effect, and allows to provide highly selective gas sensors.

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28.

Sensing properties of SnO₂-based semiconductor gas sensors to acetone and ethanol have been investigated under UV-light irradiation (peak wavelength: 365 nm) at 30°C in dry air. The responses of a pristine SnO₂ sensor showed small responses to both acetone and ethanol even under strong UV-light irradiation of 590 mW cm⁻², but the loading of Pd onto SnO₂ was effective in enhancing sensing properties to both gases. The acetone response was smaller than the ethanol response, but the response behavior was quite different between them. The mixture of ethanol into dry air definitely decreased the resistance of all the sensors, and the magnitude of ethanol response monotonically increased with an increase in the amount of Pd loaded onto SnO₂. On the other hand, the response behavior to acetone was really dependent on the amounts of Pd loaded. The small amount of Pd loaded (0.05 and 0.1 wt%) especially resulted in an abrupt increase in the resistance in mixture of acetone into dry air and a subsequent intermittent decrease in the resistance in acetone balanced with dry air. This specific behavior probably indicated that the products of partial oxidation of acetone were negatively adsorbed on the Pd-loaded SnO₂ surface first, and then they reacted with oxygen adsorbates.

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29.

The role of nonstoichiometric tungsten oxide with the composition of WO_2.72 and WO_2.90 on gas detection was investigated by using interface length effect of interdigitated Au electrodes. The long interface length of 1.5 mm was used for amplifying sensor response to 1% hydrogen. The sensor responses (S) of WO2.72, WO2.90 and WO3 showed 24.3 4.0 and 2.2, respectively. Especially, the sensor response of WO_2.72 was about ten times higher than that of WO₃. The sensor response of WO_2.72 with short interface length of 0.5 mm was 1.6. The sensor responses of WO_2.72 per both interface lengths of 1.5 mm and 0.5 mm showed same value of 1.6 /mm, suggesting that this value was related to amplifying the sensor response by increasing interface length.

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30.

In this study, the CO₂ sensors based on La₂O₃/SnO₂ stacked structures were fabricated with controlling the of deposition condition of the La₂O₃-sensitization layer. The La₂O₃ and a 100-nm-thick SnO₂ sensing layer were deposited on Pt inter-digitated electrodes. A precursor of La₂O₃ was spin-coated with the rotational velocity in the range of 1000 - 2000 rpm. The sensing area was 110 × 110 μm². CO₂ response of the devices changed with the rotational speed for spin-coating of the La₂O₃. From SEM and AES analyses, it was revealed that the La₂O₃ has porous structure and it was found that CO₂ adsorption on La₂O₃ itself is linked to the CO₂ response.

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31.

In this study, we tried to improve the sensor response of the MEMS-type gas sensor to ethanol using pulse type heating and its specific sensing characteristics. Thin (10 μm) and thick (50 μm) SnO₂ sensing films were prepared on the MEMS device, and their sensor response to ethanol and hydrogen were measured based on the two types of the determination on the sensor response; one is the sensor response at initial term in pulse heating (Si) and another is the sensor response at end term in pulse heating (Se). As a result, Si was strongly higher than Se, especially in the response to ethanol regardless of the thickness of sensing film. Additionally, high sensor response value, Si, was achieved using the thick SnO₂ sensor not only to the ethanol but also to hydrogen.

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32.

Since the accident of Fukushima Daiichi Nuclear Power Station caused by the Great East Japan Earthquake, higher safety has been required for the nuclear power plants.　In order to prevent hydrogen explosion, we need to monitor the oxygen concentration in the PCV (Primary Containment Vessel) during the severe accident.　We considered that the limiting current type　oxygen sensor is promising as a measurement device that can be used under the condition inside the PCV at the severe accident.　We evaluated the properties of a sensor using platinum or gold as the electrode material. We verified that the sensor with platinum electrode indicated low value when hydrogen and oxygen coexist. On the other hand, this phenomenon did not occur for the sensor with gold electrode. From this result, we verified the possibility of measuring the oxygen concentration in the environment of PCV where hydrogen and oxygen coexist by setting the limiting current type oxygen sensor with gold electrode.

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33.

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

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34.

A novel optical sensor using platinum-loaded tungsten oxide (Pt/WO₃) and silicon microring-resonator (MRR) for detection of hydrogen gas at room temperature was proposed and tested. The sensing principle is mainly based on the resonant wavelength shift caused by the catalytic combustion reaction of hydrogen. In the previous study, it was found that Pt/WO₃ film could not be deposited uniformly on the surface of the MRR. In order to solve this problem, acetylene glycol surfactant was used and mixed with Pt/WO₃ precursor solution. Field emission electron probe micro analyzer (FE-EPMA) images of the device surface showed that the Pt/WO₃ layer successfully covered the target part of the MRR. A 580 pm resonant wavelength shift was observed with exposure to hydrogen gas. The sensitivity of the developed device was about 4 times larger than that of the previous one.

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35.

Human breath from lever and renal disease patients are known to increase to 15 ppm or higher. Therefore, exhaled NH₃ can be a biomarker in a non-invasive breath test for such diseases. We reported that the Pt sensing electrode covered with the bead-milled hexagonal boron nitride (h-BN) increased the EMF response. However, the smaller size (0.15 m) of h-BN than the bead-milled ones was not effective for EMF enhancement. The FT-IR observation of the bead-milled h-BN suggested the formation of B-OH group in the h-BN crystal by the mechanical cleavage of the B-N bond. We concluded that the formed B-OH groups acted as a Brønsted acid site for the ammonia adsorption.

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36.

As nitrogen oxides (NOx) are one of the causatives of air pollution as well as markers of medical diagnosis, needs of high performance NOx sensors are increasing for these gas monitoring. Zeolites are known as porous materials having a good molecular sieve function, but it is difficult to apply electrode materials for gas sensors due to their high electric resistance. Then, we applied new sensor structure with solid electrolyte and zeolite as a transducer and receptor, respectively, in which the high resistances of zeolites are not significantly influence to the sensor device. In this study, the effects of the kinds of cations in zeolite on the NOx response properties were also investigated. It was found that the impedance response of the potassium doped Y-type zeolite / Na₅DySi₄O₁₂ device showed high sensitivity and sensitivity to NO at 400ºC, 50 Hz.

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