Vol. 38, Supplement B (2022)

17.

Ammonium ion-selective electrode using nonactin (before and after exercise test) were evaluated by GCIB-TOF-SIMS and SEM-EDX analyses. From the result of GCIB-TOF-SIMS, it was suggested that potassium ions as well as ammonium ions were captured by nonactin and that these ions were uniformly distributed in the bioreceptor layer. SEM analysis revealed that the peeling occurred at the interface between carbon and silver wiring after the exercise test. In addition, a new layer, which was not observed in the new electrode, was created between the bioreceptor layer and the carbon after the exercise test. EDX imaging result indicated that the potassium was present in the new layer. It was suggested that the PEDOT: PSS, which was applied on the carbon, captured the potassium ion when the potassium ion moved to the carbon through the bioreceptor layer. Peeling and new layer formation were expected to cause deterioration of the electrical properties of the electrode. In addition, we also carried out the elution tests and interaction analysis between nonactin and ions.

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清山賞受賞講演1

In this paper, we first introduce one of the studies that won the Seiyama Prize and the studies that we are currently working on. First, we introduce an on-chip graphene biosensor that detects some important proteins such as cancer markers using the surface of monolayer graphene modified with fluorescently labeled aptamers. Next, we report on the electrochemical analysis in a bicontinuous microemulsion solution using the β-cyclodextrin modified monolayer graphene electrode. Lastly, we report the characteristic properties of monolayer graphene electrodes in electrochemical detection, which depend on the potassium ion concentration in the sample solution.

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特別講演

It has been more than 50 years since the biosensors were first created, and during this time, significant advances in underlying technologies, such as artificial design and synthesis of biomaterials using genetic engineering, and the development of transducers and information technologies, have led to the development of biosensing and even biomimetic sensing. The present paper describes the progress of underlying technologies and future prospects for biosensing, focusing on the research of mine and collaborators. In this presentation, I would like to introduce several topics such as synthesis and application of artificial antibodies incorporating a nonnatural fluorescent amino acid, monitoring of intracellular reactions by surface plasmon resonance imaging, and cell-viability sensing using electric field orientation phenomena, etc.

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18.

The human sense of smell discriminates different odors by mirror-image isomers of aromatic compounds. The distinction between mirror isomers is important for physiological activity of molecules (human biological responses) because mirror isomers interact differently with biomolecules. However, there is no rapid method that identify the chirality of trace amount of gas components. In this work, we develop semiconductor gas sensors that can detect chirality of gaseous molecules by composing asymmetric environment in sensing materials. We use CsCuCl₃ as a chiral material. CsCuCl₃ is composed of helical crystal structure and is easily obtained by dissolving cesium chloride and copper chloride in water and their evaporation. However, the crystals obtained simply by evaporation are racemic twins, resulting in non-chiral materials. Homo-chiral CsCuCl₃ crystals are synthesized by adding tartaric acid. Since CsCuCl₃ is not conductive, 10 wt% Pt-SnO₂ isused as the sensing material that are operated at a low temperature, and CsCuCl₃ is used as an adsorption layer. The responses of the devices to 1-phenylethylamine and pinene are measured. The sensor showed a selective response to (R)-1-phenylethylamine when (S)-CsCuCl₃ is used as an adsorption layer, while the sensor using (R)-CsCuCl₃ showed a selective response to (S)-1-phenylethylamine. Similarly, the sensors show chiral-selective responses to (R)- and (S)-pinene.

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The purpose of this study was to identify high-entropy cation sources useful for gas detection by focusing on high-entropy oxides (HEOs) as gas sensor materials based on spinel-type composite oxides. The response of HEOs to the test gases (7 ppm NO₂, 5000 ppm H₂, 3 ppm NH₃, and 3 ppm H₂S) was investigated. The results showed that (CrFeMnNiZn)₃O₄ exhibited a high sensor response to 3 ppm H₂S. This sensor response was higher than that of Ni ferrite with two cationic elements and Ni-Zn ferrite with three cationic elements reported previously, suggesting that high-entropy oxides with near equimolar combinations of five cations from six elements are useful for increasing the sensitivity of spinel-type composite oxide gas sensors.

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20.

Nano-sized SmFeO₃ particles are prepared by the pyrolysis of heteronuclear cyano-complex, Sm[Fe(CN)₆]･4H₂O at a temperature of 600℃ in ozone. The low temperature decomposition in ozone flowing successfully yielded fine particles with a high specific surface area of 20.0 m²/g (sample A). The fine particles were classified into further smaller particles with a unimodal size distribution and this process yielded the higher specific surface area of 26.0 m²/g (sample B). Sensor electrodes consisting of those particles were formed by electrophoretic deposition (EPD) and tested on their sensing properties to the VOCs of ethanol, toluene, hexane, and toluene. The sensors with sample A and B both showed good responses to ethanol at 285 and 320℃. The sensor with sample B showed extraordinarily good selectivity of ethanol for toluene at 320℃. This could be because the detection film of sample B with moderately grown particles selectively reduced the reaction activity of toluene. The sensor with sample B also exhibited good selectivity of ethanol for hexane and dichloromethane.

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21.

Tin oxide-based semiconductor gas sensors detect inflammable gases by the change in their electroconductivity under exposure to a reducing gas. The gas sensitivity of SnO₂ increases by the addition of noble metals (Pt and Pd) owning to the activation of their reactivity to gases or an increase in the number of adsorbed oxygen due to the spillover effect. However, the relationship between gas sensitivity and the effect of noble metal loading on a sensing mechanism has not been fully understood. In this work, we elucidate the effect of the amount of Pt on the ethanol-sensing mechanism of Pt/SnO₂ by in situ spectroscopy (IR and UV-Vis). Pt/SnO₂ (0-20 wt%) is prepared by a liquid-phase synthesis method. Pt exists as atomic and particulate Pt in SnO₂ depending on the amount of Pt. Pt/SnO₂ (10 wt%) shows the largest sensor response (r.t.-400℃). The intermediates of ethanol oxidation are different depending on the amount of Pt. Reduced Sn²⁺ is confirmed during EtOH/N₂ flowing for SnO₂ while Pt/SnO₂ does not proceed with surface reduction, indicating that gaseous oxygen is responsible for ethanol oxidation on a Pt surface and a surface adsorbate affects a sensor response.

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22.

Multivariate analysis and machine learning can perform using sensor signals (resistances) obtained from a semiconductor gas sensor array to classify and identify gas species. When target gases are generated and their concentration increase and become constant, resistances of sensors also become constant. Response values of sensors are obtained from the resistances at this time, and the response values are used to determine for gas species and gas concentrations. Since a waiting time is required until the resistances change sufficiently, if the gas type can be discriminated during the waiting time, it can be expected to be applied to ventilation system for rapid ventilating before reaching odor filling, for example. In this presentation, we report a method for early discrimination of gas species using linear discriminant analysis (LDA).

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23.

Yttria-stabilized zirconia (YSZ)-based potentiometric sensors using an Au-added Pt sensing electrode (SE) and a Pt counter electrode were fabricated, and their sensing properties to CO and H₂ balanced with base gas (3% O₂ in N₂) were examined. The output voltage, E, of all sensors negatively shifted upon exposure to CO and H₂, and their responses (ΔE) increased with increasing the SE thickness. In addition, the H₂ response of the sensors was larger than the CO response in the examined SE thickness range. The electrochemical reactions at triple-phase boundaries (TPBs) of the SE of the sensors were also discussed on the basis of the electrochemical impedance properties. The introduction of CO and H₂ into the base gas decreased and increased the charge-transfer resistances at the TPBs of the SE of the sensors using the thinnest and the thickest SEs, respectively.

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24.

Electrochemical gas sensors using solid electrolytes are promising devices because of their compact structure, simple detection mechanism, and high selectivity to combustible gases. However, the conventional electrochemical gas sensors such as yttrium stabilized zirconia, and CeO₂ etc, needs high power consumption because of their high working temperature. To overcome these drawbacks, we report proton conductive graphene-based electrochemical sensors that operate at room temperature. We synthesize graphene oxide by the Tour’s method, and fabricated the membrane. Pt-SnO₂ is used as the sensing electrode and a conductive carbon is utilized as the reference electrode. The sensor device shows a sensor response of 125 mV to 200 ppm CO at room temperature.

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25.

An electrochemical gas sensor using a proton-conducting polymer membrane (Nafion) attached with Au and Pt (Au/Pt) electrodes (Au/Pt sensor) was fabricated and its CO-sensing properties were examined in this study. The current at ca. +0.16 V and in the range of −0.2 V to −0.8 V in the cyclic voltammogram largely increased upon exposure to CO and increased with an increase in CO concentration at 30°C. The Au/Au sensor also showed an increase in the current at ca. +0.16 V upon exposure to CO, while the Pt/Pt sensor showed an increase in the current in the wide range of +0.2 to +0.8 V upon exposure to CO. This behavior indicates that CO is oxidized at the Au and Pt electrodes at the different applied potentials. On the other hand, the Au/Pt sensor showed a significant increase in the current at ca. +0.29 V upon exposure to H₂, whereas the current increase was observed at ca. +0.16 V for CO. The electromotive force of the Au/Pt sensor positively shifted upon exposure to CO and H₂, and it was linearly correlated with the logarithm of concentration of CO and H₂.

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26.

Ammonia gas in exhaled breath is important biomarker of liver and renal diseases. We previously reported the use of polystyrene (PSt)@PANI core-shell spherical particles as a sensing material characterized by high sensitivity. However, reducing the response time was the problem to be solved. In this study, effects of dopant molecules on the characteristics of PSt@PANI sensors were investigated. Four different dopants such as poly(2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS), sulfosalicylic acid(SSA), poly(sodium 4-styrenesulfonate)(PSS), and sulfuric acid were used for this purpose. When doped with PAMPS or PSS, the response value was reduced to less than half compared to the sensor doped with sulfuric acid, but the response time, which was more than 20 min, was successfully shortened to several minutes.

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27.

Nonanal has been reported to be detected at higher concentrations in the exhaled air of lung cancer patients than of in healthy individuals. Therefore, it is attracting attention as a non-invasive biomarker for lung cancer. In this study, we focused on the reaction between triphenylmethane (TPM) dye and nonanal, and developed a nonanal detection chip that combines TPM dye and porous glass. The reaction products were decomposed in solution system, on the other hand, they were stable in the porous glass. The nonanal concentration could be calculated from the absorbance difference at 620 nm of the detection chip. The detection limit was calculated to be 2 ppb, which was at the same level as the cut-off value of nonanal concentration in exhaled breath of lung cancer patients and healthy subjects.

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28.

Poly(N-isopropylacrylamide) (pNIPAM) has the property of reversibly adsorbing large amounts of HCl gas. We have chosen pNIPAM as sensing films for a mass-sensitive HCl gas sensors operable at room temperature. However, the response time and recovery rate still needed to be improved for practical use. In this study, porous pNIPAM gel thin films were prepared by using bicontinuous microemulsions (BME). A BME has nanosized three-dimensional continuous networks composed of water and oil phases. By using water phase in BME as a reaction field for cross-linking polymerization, porous pNIPAM gel thin film having smaller pores with 100 nm in diameter was obtained. The HCl gas adsorption properties of the fabricated porous pNIPAM gel thin films were investigated. Compared with the pNIPAM gel film prepared in water, the amount of adsorption of the porous gel film prepared in BME increased about twice. Furthermore, the response time was reduced from 28 min to 1 min as expected.

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清山賞受賞講演2

This article reviews our recent progress in developing solid electrolyte-type and semiconductor gas sensors. We found that toluene response of YSZ-based potentiometric sensors was improved by the addition of CeO₂ to a Au sensing electrode (SE) due to an increase in the electrochemical activity of toluene oxidation. The toluene response of the sensors attached with a 24 wt% CeO₂-added Au SE increased with an increase in the SE thickness, which is an opposite trend for the sensors attached with an 8 wt% CeO₂-added Au SE. In addition, we reported that NASICON (Na₃Zr₂Si₂PO₁₂)-based potentiometric gas sensors using a Bi₂O₃-added Pt SE showed a large CO response to a positive direction at 30°C as well as that to a negative direction of the sensor using a CeO₂-added Pt SE. We also demonstrated that the introduction of porous structure into Au-added In₂O₃ and Ru-loaded WO₃ improved the gas diffusivity of these materials as well as the dispersion of Au and Ru in these oxides to enhance the sensing properties of NO₂ and methyl mercaptan, respectively.

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29.

New catalytic combustion-type H₂ gas sensors were devised by applying 7 wt% Pt / Eu₁₀(Si_1−xMn_x)₆O_27−δ as the H₂ oxidizing catalyst. By applying Eu₁₀(Si_1−xMn_x)₆O_27−δ solids as the promoter for catalyst, oxygen species were efficiently supplied to Pt activator, which realized H₂ combustion at low temperatures. Among the catalysts prepared, the 7 wt% Pt loaded Eu₁₀(Si_0.90Mn_0.10)₆O_27−δ catalyst showed the highest H₂ oxidizing activity and the sensor with this catalyst detected H₂ gas concentration with an excellent linearity between sensor output and H₂ gas concentration changes even at room temperature. Furthermore, the present sensor showed rapid 90% response of ca. 13s at room temperature.

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30.

The catalytic combustion type micro gas sensors utilizing 15wt%M/γ-Al₂O₃ (M = Pt, Pd, Rh, Ru, Au) were fabricated and response properties to carbon monoxide have been investigated. Among the sensors prepared, the sensor utilizing 15wt%Pt/γ-Al₂O₃ showed a large response peak (adsorption/combustion peak) on the pulse-driven heating for 0.1 seconds with a cycle of 30 seconds, while other sensors did not show such a response peak.　The height of adsorption/combustion peak increased with increasing the amount of Pt in Pt/γ-Al₂O₃ and the sensor utilizing 40wt%Pt/γ-Al₂O₃ showed the largest response peak. According to the measurement of specific surface area and　metal surface area of Pt/γ-Al₂O₃, the metal surface area of Pt/γ-Al₂O₃ increased with increasing the amount of Pt, while the specific surface area decreased. This result indicates that the adsorption/combustion peak to CO based on the CO adsorption to Pt metal. The present micro gas sensor realized higher sensitivity and selectivity to CO by optimizing the catalyst material, the operating condition such as the temperature and the period of the pulse heating.

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31.

In this study, a Bayesian optimization approach to determining an optimal parameter set for temperature modulation is proposed. Two parameters of heater voltage for temperature modulation to classify six gas mixtures were optimized. Bayesian optimization was carried out to minimize Davies-Bouldin index (DBI), an objective function. After successful reduction of DBI through nine trials, it was revealed that the classification accuracy overall increased with decreasing DBI, indicating that DBI acted as a good objective function. Consequently, it was demonstrated that the proposed method was promising with improved classification accuracy from 59.2 % to 76.3 %. Furthermore, the applicability of the method to selective gas detection was also suggested.

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32.

We demonstrated adaptive discrimination of odors in various categories by a single metal oxide gas sensor based on optimizing the modulated waveform for sensor temperature modulation. The parameters of modulated waveform for discriminating six mixed gases and five spices were optimized by Bayesian optimization. The data matrices were constructed based on the sensor conductance, and the discrimination accuracies for mixed gases and spices were evaluated. The results show that high discrimination accuracies were achieved for both mixed gases and spices, with different optimal parameters. These results indicate that we can adaptively discriminate various odors with a single metal oxide gas sensor by optimizing the parameters of the modulated waveform depending on odor categories to be discriminated.

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33.

Polymerase chain reaction (PCR) and antigen tests are performed for infection with the new coronavirus. These methods are useful as tests when infection with the new coronavirus is strongly suspected. However, since these methods need to be performed by operators with specialized skills, it is desired to develop novel method that can be easily performed on a daily screening application for respiratory. Since the semiconductive gas sensors can perform on real-time monitoring, gas species would be able to be discriminated immediately by applying the obtained sensor signal to machine learning. In this presentation, we selected 7 kinds of VOCs by referring to the reports of VOCs contained in exhaled breath of respiratory disease patients, and report applying sensor signals to a neural network for outputting VOC species and their concentrations.

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