Vol. 38, Supplement A (2022)

1.

Semiconductor VOC gas sensors with SmFeO₃ detection layer were fabricated by the electrophoretic deposition (EPD). SmFeO₃ powder was deposited on an alumina substrate with Au comb-shaped electrodes with different thicknesses. Homogeneous SmFeO₃ films were formed with deposition time of > 5min at an applied voltage of 5 V. Base resistance of the sensor elements decreased with the increase in film thickness. The sensors with deposition time of 5 min and 7 min at 300°C were examined in ethanol, hexane, toluene and dichloromethane. The sensor of 5 min showed larger response to ethanol than hexane (R_gas / R_air = 4.5 for 5 ppm ethanol and 2.0 for 5ppm hexane). On the other hand, the sensor of 7 min exhibited larger response to hexane than ethanol (R_gas / R_air = 3.0 for 5 ppm ethanol and 4.7 for 5 ppm hexane). Since the surface of SmFeO₃ is rather basic, ethanol with acid property strongly adsorbs on SmFeO₃ and reacts on the surface of the detection film, which decreases sensor response in the case of a thick film. On the other hand, hexane probably weakly adsorb on SmFeO₃ and more easily diffuse into the bulk of the film. The sensors showed low response to both toluene and dichloromethane regardless of deposition time.

To Japanese Contents　／　To English Contents

2.

Spherical porous (pr-)SnO₂-based particles (pr-SnO₂, 2.0 wt% CuO-added pr-SnO₂ (pr-2.0CuO-SnO₂), and w wt% Au-added pr-2.0CuO-SnO₂ (pr-wAu-2.0CuO-SnO₂, w: 0.5–5.0), were prepared by ultrasonic spray pyrolysis employing home-made PMMA microspheres (typical particle size: 70 nm in diameter). Besides, an appropriate amount (w wt%) of Au was loaded on pr-2.0CuO-SnO₂ particles (wAu/pr-2.0CuO-SnO₂) by a conventional impregnation method. Their VOC-sensing properties were examined at 300–500°C in air. The pr-2.0CuO-SnO₂ sensor showed a larger acetone response than the pr-SnO₂ sensor in a temperature range examined. Furthermore, the addition of Au to the spherical pr-2.0CuO-SnO₂ particles improved the acetone response, and the pr-3.0Au-2.0CuO-SnO₂ sensor showed the largest acetone response at 350°C among the sensors tested. The pr-3.0Au-2.0CuO-SnO₂ sensor prepared by ultrasonic spray pyrolysis showed a larger acetone response than the 3.0Au/pr-2.0CuO-SnO₂ sensor prepared by a conventional impregnation method. The pr-3.0Au-2.0CuO-SnO₂ sensor showed an almost linear relationship between the response and the acetone concentration (2.5‒100 ppm) in double logarithmic scale, with the capability of ppb-level acetone detection.

To Japanese Contents　／　To English Contents

3.

We are investigating a simple simultaneous detection method for acetone and NO in exhaled air using a porous glass-based gas detection chip. In this study, we evaluated the reactivity of acetone and NO when the acetone detection chip and NOx detection chip were used in combination. As a result, in the simultaneous analysis, acetone was adsorbed on the NOx detection chip, and NO₂ converted by the NO/NO₂ conversion chip was adsorbed on the acetone detection chip; The slopes of the calibration curves for the combined detection chips were 1.33 and 1.59 times for the acetone and NOx detection chips, respectively.

To Japanese Contents　／　To English Contents

4.

A CO sensor using c-axis oriented oxyapatite lanthanum silicate (c-LSBO) as a solid electrolyte, which exhibits oxide ion conductivity about 190 times higher than that of YSZ at 400°C has been investigated. The CO detection properties of electromotive force (E.M.F.) and short-circuit current as sensing signals were examined using Au and Pt + La_0.6Sr_0.4Co_0.78Fe_0.2Ni_0.02 (LSCFN) as a sensing electrode and a counter electrode, respectively. As results, it was found that the E.M.F. and short-circuit current values quickly change and scale linearly with the logarithm of CO concentration in the range of 0-800 ppm at 500℃.

To Japanese Contents　／　To English Contents

5.

Human exhaled breath contains various volatile organic compounds, some of them can be closely related to the particular diseases. Especially, acetone is included in high concentration in the exhaled air of patients with diabetes and expected as a non-invasive biomarker for diabetes. We had developed an acetone analytical chip using 2-nitrophenylhydrazine (2-NPH) and porous glass to detect acetone gas, and the developed chip exhibited new absorption peak at 446 nm after exposure to acetone. In this study, we assembled a real-time measurement device using a blue laser with a wavelength of around 450 nm and two photodiodes (PDs). The absorbance could be calculated from the PDs’ voltage ratio. There was a linear relationship between the absorbance measured by the spectrometer and the absorbance calculated by the voltage ratio, and it was found that the acetone concentration (1.82~10.01 ppm) could be calculated using the voltage ratio with the flow velocity of 0.05 L min-1. By using the developed device, the acetone concentration could be measured every 4 minutes.

To Japanese Contents　／　To English Contents

6.

In this study, a thin-film temperature and humidity sensor with transparency, flexibility, and high gas permeability was realized by using ionic liquid gel as the sensing material. This sensor can selectively detect temperature and humidity by introducing ionic liquids with different hydrophilicity into two ion gels. The sensor was fabricated by spray coating carbon nanotube electrodes and ion gel on a silicone elastomer substrate. The temperature sensor using hydrophobic ion gel showed high output stability (±5 % in impedance) against humidity change. In contrast, the humidity sensor using hydrophilic ion gel showed high sensitivity to temperature and humidity changes (2.5 %/ relative humidity in impedance). By calibrating the output value of the humidity sensor using the temperature sensor, selective detection of temperature and humidity was realized.

To Japanese Contents　／　To English Contents

7.

Nonanal has been reported to be detected at higher concentrations in the exhaled air of lung cancer patients than 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 Schiff's reagent and nonanal, and developed a nonanal detection chip consisting of Schiff's reagent and porous glass. In order to detect nonanal at ppb level, we compared the reactivity of two types of detection chips fabricated using different acids, and investigated the composition that enables more sensitive detection. The developed detection chip showed that the Schiff reagent showed absorption at 534 nm (citric acid) and 540 nm (acetic acid), and the reaction product showed absorption at 600 nm. There was a positive correlation between absorbance difference at 600 nm and nonanal concentration. The difference in absorbance between 534 nm (or 540 nm) and 600 nm could be used to calculate the concentration of exposed nonanal when the samples were allowed to stand for 24 hours after 3 hours of exposure. The lower limit of detection of the developed nonanal detection chip was 16 ppb.

To Japanese Contents　／　To English Contents

8.

Hydrogen sensing performances of Pt/WO₃-SiO₂ composite film and Pt/WO₃ film were compared and evaluated. The films were prepared by sol-gel and spin-coating method on quartz glass substrate, and annealed at 200℃ and 500℃. Both films were exposed to 4 vol.% H₂/Air gas and the transmittance changes during coloring and bleaching process were measured. Pt/WO₃-SiO₂ composite film annealed at 200℃ showed remarkable response kinetics; the sensitivity declined, but bleaching time was much shorter than that of Pt/WO₃ film annealed at same temperature. Furthermore, bleaching rate was maintained for 1 month after the film preparation. Comparing with response behavior upon exposure to 4 vol.% H₂/Ar gas, it was considered that the coloring reaction of composite film was impeded by oxygen in the air due to the existence of SiO₂, leading to declined sensitivity and promoted bleaching reaction.

To Japanese Contents　／　To English Contents

9.

We proposed a flexible ammonia gas sensor using polyaniline graft film. The sensor had a three-layer structure consisting of a flexible polyethylene terephthalate (PET) film, a polydopamine thin film, and the grafted polyaniline doped with H₂SO₄. The sensor showed a great and reproducible response toward NH₃ gas. Furthermore, the hydrophilization treatment of the PET film was effective in increasing the response value. The obtained magnitude of the sensor response (△R/R_N2) was 35 for 250 ppm dry NH₃ gas at 50 °C.

To Japanese Contents　／　To English Contents

10.

Catalytic combustion-type CH₄ gas sensors were devised by applying 11.3 wt% PdO / 16 wt% Ce_0.8(1−x)Zr_0.2(1−x)NixO_2.0−δ / γ-Al₂O₃ as the CH₄ oxidizing catalyst and their CH₄ sensing performance were investigated. By combining CeO₂-ZrO₂-NiO solids showing the high oxygen storage and release ability as the promoter with PdO, oxide ions in the CeO₂-ZrO₂-NiO solids can be supplied to PdO, which realizes CH₄ combustion reaction even at low temperatures. Among the catalysts prepared, it was revealed that the 11.3 wt% PdO / 16 wt% Ce_0.68Zr_0.17Ni_0.15O_2.0−δ / γ-Al₂O₃ catalyst possessed the highest CH₄ oxidizing ability and the sensor using this catalyst can detect CH₄ gas concentration stably and quantitatively with the 90% response time of ca. 10s even at 290°C.

To Japanese Contents　／　To English Contents

11.

To improve the sensor response to low concentration methane in high humid atmosphere, Pd nanoparticles were loaded on the SnO₂ nanoparticles via two different processes: one is an impregnation-based process to prepare an IM-Pd/SnO₂, and the other is a colloidal protection method-based process to prepare a CP-Pd/SnO₂. According to the TEM-EDX results, Pd nanoparticles size and dispersity of the CP-Pd/SnO₂ were larger and higher, respectively, than these of IM-Pd/SnO₂. The CP-Pd/SnO₂ exhibited a higher sensor response to methane than that of IM-Pd/SnO₂ at low operating temperature (250°C) in humid atmosphere. Such difference in the sensor response was caused by methane oxidation activity in different particles size and dispersity of Pd nanoparticles.

To Japanese Contents　／　To English Contents

12.

ZnO nanorods have been attracted much attention as a gas sensing material owning to their anisotropic morphology and gas diffusibility. However, high temperature (>300oC) is required for their operation and it causes deterioration of sensing materials. In this work, we consider the sensitization of ZnO nanorod gas sensors by light-irradiation and Pt deposition. ZnO nanorods are hydrothermally grown on alumina substrate and Pt nanoparticles are supported on ZnO nanorods from Pt-phosphoethanolamine complexes. The sensitivity of Pt/ZnO (50 ppm EtOH/air, S = 843) is 119 times higher than that of ZnO nanorods (S = 7) at 150°C under light irradiation (AM-1.5G). The oxidation ability of Pt/ZnO nanorods to ethanol is the most active under light-irradiation at 150oC, leading to high sensitivity.

To Japanese Contents　／　To English Contents

13.

Porous (pr-)In₂O₃ spherical particles loaded with and without Au were prepared by ultrasonic spray pyrolysis (typical particle size: 70 nm in diameter), and effects of the Au loading onto pr-In₂O₃ on the NO₂ sensing properties were discussed on the basis of gas adsorption properties of their sensors at 100°C by using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The resistance of the Au/pr-In₂O₃ sensor in dry air was lower than that of the pr-In₂O₃ sensor. The DRIFT spectra of both the sensors showed broad positive bands between 1600 cm⁻¹ and 1000 cm⁻¹ in dry air at 100°C (reference: dry N₂), which originated mainly from oxygen adsorbates and/or lattice oxygen, and that the bands were much larger for the Au/pr-In₂O₃ sensor than for the pr-In2O3 sensor. The Au loading also increased the adsorption amount of H2O on the pr-In2O3 surface. In addition, the absorbability of NO₂ onto the pr-In₂O₃ surface was enhanced by the Au loading even in the coexistence of O₂, which contributed to the large NO₂ response of the Au/pr-In₂O₃ sensor.

To Japanese Contents　／　To English Contents

14.

Semiconductor gas sensors using SnO₂ as a base material are required to have higher sensitivity and selectivity to VOC gases due to recent requirements in medical and environmental measurements. In this study, we focused on the acid-base property of the material surface and investigated the effect of the addition of oxides to the SnO₂ particle surface on the VOC gases detection properties. SnO₂ was modified using MoO₃, which is more acidic than SnO₂, as a receptor, and the effects of the acidity of the material surface on the VOCs response properties and the response mechanism were investigated.

To Japanese Contents　／　To English Contents

15.

In order to clarify the correlation between the driving pleasure felt by the car driver and the exhaled breath, a commercially available spirometer and a semiconductor sensor that detects volatile organic compounds (VOC) are used to detect the exhaled breath of the subject driving the drive simulator. Fluctuations in each parameter of oxygen consumption, carbon dioxide excretion, respiratory rate, etc. and VOC concentration in exhaled breath during driving were monitored. After driving, participants assessed "enjoyment" and "difficulty" of courses on a scale of one to seven. We examined whether there was a correlation between the questionnaire results and the mean and standard deviation of each parameter of breath.

To Japanese Contents　／　To English Contents

特別講演1

From 2008 to 2013, we performed the “Human Sensing Fusion” project supported by Japan Science and Technology Agency. This research project aimed to realize a human activity monitoring system that can be attached directly to the human body without any restrictions in daily life. In order to realize such a device, it is essential to make it small in size and low in power consumption. We used MEMS technology, and studied a wide range of fields including many kind of sensors, power generators, flexible electronics, low-power radio, and demonstration system. After the project was completed, some of the project members established a venture company and started commercial production of monitoring systems based on the results of the project. In this paper, after a brief description of MEMS technology, the specific human activity monitoring system delivered by the venture company will be described.

To Japanese Contents　／　To English Contents

特別講演2

A variety of odor sensors have been developed in the world. Some of them reveal the components of odor, some of them detect specific odor molecules with ultra-high sensitivity, and some of them monitor various phenomena from a group of odor molecules in a specific category. We have developed a human olfactory receptor cell array sensor that can comprehensively detect all odors (from simple to complex) perceived by humans using all human olfactory receptors, which are sensing molecules of human olfaction. In this talk, we will introduce the development process of this sensor and examples of social implementation that can only be achieved with this sensor.

To Japanese Contents　／　To English Contents

16.

Lipid membranes have been used in a taste sensing system for a long time. Among the lipids, phosphoric acid di-n-decyl ester (PADE) has been widely used in the membranes for sensing bitterness and saltiness. However, the dissociation degree dependent on pH has caused the results of measurements neither accurate nor stable enough. To solve this problem, tetrakis [3,5-bis (trifluoromethyl) phenyl] borate sodium salt dehydrate (TFPB) was selected because it is completely dissociated. It was expected that membranes composing of this substance can behave both sensitively and stably; however, the strong selectivity to univalent ions and much lower electrochemical impedance occurred to be problems. In this study, the electrical properties of two kinds of lipids used in membranes of taste sensor have been explored in-depth. Experiments on univalent cation (Li⁺, Na⁺, K⁺, Cs⁺) selectivity and electrochemical impedance have been carried out. As a result, the membranes using PADE sustained a low selectivity on univalent cations and a high electrochemical impedance at all the PADE concentrations. Those using TFPB tended to show low selectivity and high impedance at extremely low TFPB concentrations, and high selectivity and low impedance being decayed over 103 times lower at the higher concentrations. It is expected that the results in this study can contribute to improvement of membrane components.

To Japanese Contents　／　To English Contents