Vol. 34, Supplement B (2018)

17.

Discrimination of fungi Aspergillus species is important in food-contamination testing as well as clinical diagnosis. Conventionally, microscopic observation of cell morphology, genetic analyses and immunoassay are employed for this purpose. However, these methods are time-consuming and labor-intensive. We have proposed a rapid and simple method for discrimination of microorganisms called “colony fingerprinting”. In colony fingerprinting, discrimination was carried out based on multivariate analyses of the colony images, called “colony fingerprints”, which were obtained by a wide-field of view lens-less imaging system. The imaging system is composed of a complementary metal oxide semiconductor (CMOS) sensor and LED light, and enables to visualize microcolonies with the size of sub-millimeter scale. Therefore, the assay time can be short as compared to conventional methods. In our previous study, we demonstrated that colony fingerprinting was useful for discrimination of bacteria. In this study, we applied this method for discrimination of four closely related Aspergillus species (A. oryzae, A. niger, A. nomius, and A. flavus). Using support vector machine (SVM) as a classifier, discrimination of these fungi was successfully demonstrated with 95% of accuracy. This result suggests that the colony fingerprinting is a promising method for fungal discrimination.

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18.

The rapid and easy detection of biomolecules is a very important technique for early detection of disease and prevention of the spread of harmful microorganisms. Molecular recognition by hybridization of DNA is often used for biomolecule detection. The method has high selectivity and is also versatile. So far, we have developed a sensing system that captures targets DNA and electrochemically detects them with nanoparticles modified with base chains complementary to target DNA1). This system provided selective detection of pico-mol level against targets. However, this system requires apparatus for electrochemical measurement, and B / F separation step is necessary. Therefore, in this research, we focused on a technique that analyzes the diffusion behavior of particles in liquid2). We　designed a system to quantify DNA from its diffusion behavior by forming a complex with probe particles (Fig. 1). We expect that when the target DNA forms a complex with nanoparticles, the diffusion rate will decrease due to the increase in particle size. It is considered that the size of DNA complex increases with increasing DNA concentration and diffusibility decreases.

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A simple detection system based on dielectrophoresis (DEP) of particles modified with aptamer has been investigated in the presentation. The aptamer for thrombin (model target in this presentation) was immobilized on the surface of particles (500 nm diameter) via crosslinking agent (sulfo-SMCC). The suspension of the particles modified with aptamer was mixed with solutions containing different concentrations of thrombin, and injected into the channel of devices for the DEP manipulation. The interdigitated array of microband with the shape of the teeth of a saw was arranged in the channel for the particle manipulation based on the DEP. The particles were broadly accumulated above the band electrode by applying AC voltage with high frequency region due to the effect of negative DEP. In contrast, the particles were trapped at the region between the teeth of a saw with low frequency region by the effect of positive DEP. This, we can easily find the cross-over frequency which is the frequency without forces of both positive and negative DEP. The cross-over frequencies for the particles in different concentrations of thrombin were estimated. The cross-over frequency decreased with increasing the concentration of thrombin. The decrease of the cross-over frequency could be due to the decrease of the surface conductivity of particles by capturing of thrombin to the immobilized aptamer. The present procedure is absolutely simple because of the needless of the separation step for unreacted thrombin.

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20.

M-added (M = Al, La) and pure MgFe2O4 powders were prepared from a malic acid complex, and the CO sensing properties were examined in the temperature range of 250 to 500 °C in dry air. In the XRD measurement, when M atoms were added to MgFe2O4, the crystallite growth of MgFe2O4 was suppressed remarkably in comparison with the pure material. The CO sensitivity of pure MgFe2O4 was confirmed only at 500 ºC. On the other hand, for 5 mol% La-added MgFe2O4, the CO sensitivity was improved in comparison with pure material and was estimated to be 2.9 times higher than that of pure one at 400 °C. Furthermore, 10 mol% La-added MgFe2O4 showed a higher CO sensitivity than that of 5 mol% La-added MgFe2O4 at 350 ºC.

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21.

Determination of ethanol concentration in breath air is important to avoid drunk-driving incidents. Hence, compact gas sensors are required to detect ethanol concentration accurately, quickly, and highly sensitively. For such applications, semiconductor gas sensors are promising; they can detect combustible gases at low concentrations. In this study, we focused on layered transition metal dichalcogenides (LTMDs) as new sensor materials, which are two-dimensional materials with semiconductor properties. The two-dimensional nature of these materials allows for the miniaturization the device and highly sensitive detection of gases. Indeed, there has been literature reporting that molybdenum disulfide (MoS2) binds strongly to volatile organic compounds. Here, we show that MoS2 nanosheets synthesized by a new liquid phase method exhibited a good sensing response to ethanol.

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22.

Cerium oxide possesses high diffusion coefficient for oxygen. Oxygen vacancies in surface of cerium oxide, which depend on oxygen pressure, can diffuse into its bulk. The electric resistance of cerium oxide is affected by its oxygen vacancies. The cerium oxide thick films can be used as resistive oxygen sensors. Ten percent of zirconium-doped cerium oxide (CeZr10) possesses the same oxygen sensing property as the cerium oxide and resistance level of the CeZr10 is around one-tenth of that of cerium oxide. However, the oxygen vacancies of cerium oxide and CeZr10 sensors are also developed by oxidation of combustible gases, so the cerium oxide and CeZr10 sensors cannot monitor to oxygen concentration in atmosphere with the same or more concentrations of combustible gases. In this study, we have developed catalytic layers on the CeZr10 sensor thick films for consumption of interference combustible gases.

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23.

Effects of surface modification of a SnO2 sensor with hexamethyldisiloxane (HMDSO) at 400°C on the sensing properties to hydrogen (H2) and methane (CH4) have been investigated in this study. The resistance and the magnitude of CH4 response of the SnO2 sensor monotonically decreased with an increase in the amount of HMDSO modification. On the other hand, the small amount of HMDSO modification enhanced the magnitude of H2 response of the SnO2 sensor, probably because H2 molecules easily diffused through a resultant SiO2-based layer into the SnO2 surface in comparison with O2 molecules, while the further increase in the amount of HMDSO modification decreased even the magnitude of the H2 response. In addition, the HMDSO modification decreased both H2 and CH4 sensitivities of the SnO2 sensor, and the decrease in H2 sensitivity by the HMDSO modification was significant, in comparison with that of the CH4 sensitivity.

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24.

Hot wire semiconductor type high sensitive gas sensors for the detection of volatile organic compounds (VOC) have been developed. The VOC sensor consists of platinum wire and sintered SnO2 carrying specific metal oxides. The fabricated sensor showed high sensitive to the VOC, and　it showed excellent poisoning durability against siloxane gas. The addition of the metal oxide caused a change in the oxidation activity of SnO2, and the sensor characteristics were improved. VOC sensors fabricated by micro electro mechanical systems (MEMS) technology have been also developed. The power consumption of this sensor is about 300μW. The MEMS type gas sensor showed high sensitive to the VOC.

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25.

In this study, a gas-sensitive SPIM sensor using SnO2 as sensing element is proposed, to detect local impedance changes on the sensing surface in response to ethanol vapor. This gas-imaging sensor has a field-effect structure with an air gap to form a suspended-gate structure. The local impedance changes due to the interaction between ethanol vapor and SnO2 film are observed by monitoring the photocurrent signal induced by a scanning laser beam. Furthermore, the photocurrent signal is captured in a spatially resolved manner and converted into images thanks to the light-addressability of SPIM, which can be used for visualization of the gas-concentration distribution in the gas channel.

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26.

We investigated the ion-sensitive field-effect-transistors (ISFETs) based on the AlGaN/GaN heterostructures for the chemical-sensor application. In order to improve the transconductance (gm) of open-gate ISFETs, the photo-electrochemical (PEC) etching was applied on AlGaN surface for the formation of the recessed-gate structure. The etching depth of AlGaN layer was precisely controlled by optimized PEC condition, where very smooth etched-surface was obtained with a RMS roughness of 0.6 nm. The Ids-Vds characteristics of AlGaN/GaN ISFETs were measured in a PBS electrolyte by applying the gate voltage using an Ag/AgCl electrode. The current saturation and pinch-off behavior were clearly observed. This indicates the current transport in AlGaN/GaN heterostructures was modified by the surface potential changed at open-gate area. As expectedly, the threshold voltage, Vth, was changed with the AlGaN thickness, where the normally-off operation (Vth > 0V) was obtained in the recessed-gate ISFETs with AlGaN thickness of 7.6 nm. The Ids-Vds curves of the recessed-gate ISFET showed a strong dependence on the pH value of the electrolyte. The pH-sensitivity was roughly estimated about 65µA/pH, corresponding to the gm value of 1.1 mS. The values were 1.3 times larger than those of the planar-gate ISFET.

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27.

Poly(N-isopropylacrylmide–co-Butyl methacrylate)s (P(NIPAM-BMA)) with the composition of NIPAM:BMA=10:1 and 20:1 were synthesized via free radical polymerization. A lower critical solution temperature (LCST) of these copolymers in aqueous solution were 19℃ for NIPAM : BMA = 10:1 and 14℃ for 20:1. By dropping these copolymer dispersion solutions below LCST to a quartz resonator surface and drying it, P(NIPAM-BMA) nanoparticle films were easily fabricated at room temperature. Surface observation of the nanoparticles film with SEM revealed that nanoparticles had the diameter of ~200 nm for both copolymers. Adsorption/desorption characteristics of the fabricated nanoparticle films were measured. The adsorption amount of the NIPAM-BMA copolymers to HCl gas was proportional to the loading amount on the resonator surface. The adsorption amount for the copolymer (20:1) was larger than that for the copolymer (10:1) and homopolymer, however, the recovery characteristic for the copolymer (20:1) was slightly poor compared with that of other polymers.

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清山賞受賞講演2

The development of compact sensors that can detect volatile organic compounds (VOCs) is extremely important to address air quality issues and to avoid health risk associated with VOCs. This article reviews our recent progress in developing solid electrolyte and semiconductor gas sensors for highly sensitive detection of VOCs. An overview of the exploration of a mixed-potential-type VOC sensor using oxide ion-conducting BiCuVOx (Bi2Cu0.1V0.9O5.35) fitted with perovskite oxide electrodes is provided. The importance of designing its electrode structure is discussed. Other successful development of ultrasensitive VOC sensors using SnO2 nanocrystals and nanorods is also introduced.

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28.

A new catalytic combustion-type ethanol (C2H5OH) gas sensor was devised by applying Pt-loaded La10Si5.7Co0.3O27 solid solution as the C2H5OH oxidizing catalyst. The sensor showed the superior sensing performance of smooth and rapid response to C2H5OH gas at 150°C. Moreover, since the present sensor exhibited linear response to the C2H5OH gas concentration change, it is expected that the sensor can detect C2H5OH quantitatively at the operating temperature of 150°C.

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29.

Catalytic combustion behavior of ethanol over mesoporous γ-alumina loaded with 10 wt% metal oxide (MO) and/or 1.0 wt% Pt (A/mp-Al2O3, A: 1Pt, 10MO, or 1Pt/10MO (MO: CeO2 or Bi2O3)) and temperature-programmed desorption (TPD) and temperature-programmed oxidation (TPO) characteristics of ethanol adsorbed on these mp-Al2O3-based catalysts have been investigated in this study, to clarify the ethanol-sensing mechanism as the adsorption/combustion-type gas sensors. The loading of only MO improved the ethanol conversion of mp-Al2O3. However, the magnitude of ethanol response of the 10MO/mp-Al2O3 sensors was quite small, probably because of extremely slow rate of ethanol oxidation at elevated temperatures (450°C). On the other hand, the co-loading of Pt and CeO2 onto mp-Al2O3 was the most effective in improving the oxidation activity of ethanol among all the sensor materials, and the large magnitude of ethanol response of the 1Pt/10CeO2/mp-Al2O3 sensor probably originates from the quite rapid rate of ethanol oxidation.

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30.

We have developed SiC-FET-type NOx sensor and SAW-type PM sensor for exhaust gas. SiC-FET-type NOx sensor utilizes SiC substrate and the gate layer made of yttria-stabilized zirconia, nickel oxide and platinum. The gate layer has catalytic effect for NOx and therefore the threshold voltage of the FET is sensitive to NOx. NOx concentration in the exhaust gas can be derived from the threshold voltage shift of the sensor FET. By virtue of SiC and the gate materials, the sensor has heat resistance at least up to 900ºC. SAW-type PM sensor utilizes langasite substrate and platinum electrode. The quantity of the PM adhering to the SAW device can be estimated from the frequency shift or delay time shift of SAW device. The PM sensor also has strong heat resistance and suitable for exhaust gas. The sensing principle of the FET and the SAW sensors make it possible to realize higher sensitivity compared to the conventional sensors.

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31.

We have developed SiC-FET-type NOx sensor and SAW-type PM sensor for exhaust gas． SiC-FET-type NOx sensor utilizes SiC substrate and SAW-type PM sensor utilizes langasite substrate． Both sensor electrode made of titanium layer and platinum layer． By Au stud bump on the top of platinum electrodes，SiC-substrate NOx sensor and langasite- substrate PM sensor connect ceramics substrate electrodes to assemble into an exhaust gas sensor module． The sensor modules need heat resistance at least up to 700 ºC， and also need strong gas corrosion resistance at 700ºC gas atmosphere． Joint material of those sensors has good resistance for non-methane organic gas， SO2， NO， NO2， SO2/NO/NO2　 mixed gas at 700ºC． The novel metal joint materials， Pt metallize and Au stud bump， connect SiC and langasite to ceramic substrates realize excelling connecting as a high temperature corrosion gas resistance sensor．

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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 directly in the Primary Containment Vessel (PCV) environmental condition during the severe accident. We considered that the limiting current type　oxygen sensor is promising as a direct measurement device that can be used under the condition inside the PCV at the severe accident. We confirmed a possibility that the limiting current type oxygen sensor that used gold for the electrode material could be adapted for the PCV in case of a severe accident.1) In order to improve the adaptability during a severe accident, we examined the operating condition of the oxygen sensor with which any chemical species other than oxygen do not interfere in an oxygen sensor measurement result.

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33.

Limiting current type oxygen sensor is compact and detects oxygen in a wide concentration range1. However, this sensor is required to be operated at high temperature because of insufficient oxide ion conductivity in Y2O3 stabilized zirconia (YSZ) and so, low temperature operation of limiting current type sensor is required at present from low temperature of exhaust gas from engines. The objective of this study is to develop limiting current type sensor operating at decreased temperature for achieving the high selectivity. The limiting current type sensor was prepared by using LaGaO3 based oxide for electrolyte. For electrode, Co based oxide was mainly prepared by screen printing method. Al2O3 plate with pin hole, 0.2～0.5mm in diameter, was mainly used for oxygen diffusion layer. I-V curves of the prepared limiting current sensor using LaGaO3 electrolyte is observed at temperature from 300～500℃. With decreasing operating temperature, limiting current became smaller, however, limiting current was increased with increasing oxygen partial pressure. Therefore oxygen partial pressure can be estimated from limiting current. As a result, low operating temperature limiting current type oxygen sensor is realized by using LaGaO3 fast oxide ion conductor.

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34.

Liver and renal diseases increase in ammonia concentration in human blood. Along with this, the concentration of ammonia in expiration increases. Therefore, detection of ammonia in breath exhaled from a human has a large potential to be a noninvasive pathological diagnosis. In this study, potentiometric ammonia sensors were prepared based on yttria-stabilized-zirconia (YSZ) electrolyte and Pt electrode. In our previous result, covering the Pt sensing electrode with hexagonal boron nitride (h-BN) ball-milled increased EMF response. In this study, the h-BN was mixed with Al2O3 to yield h-BN dispersion, h-BN/Al2O3. Sensor response was tested for ammonia, acetone, ethanol and hydrogen. Acetone, ethanol and hydrogen showed good responses. On the other hand, ammonia showed remarkably small response. We concluded that using Al2O3 as an auxiliary electrode selectively decreased ammonia response.

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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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