Vol. 37, Supplement A (2021)

9.

Bipolar electrochemistry provides means for promoting multiplexing. In ordinary bipolar electrochemical systems, electrodes are electrically floating and interfacial potential difference between the solution and the electrodes is not controlled. In this study, the potential difference on bipolar electrodes (BPEs) was controlled using ion-selective membranes (ISMs). By placing the ISMs on gold BPEs, the intensity of electrochemiluminescence (ECL) could be modified, as demonstrated by distinct difference in ECL intensity. The effect of the ISM was also confirmed by using folded structures consisting of two connected BPEs with the ISMs placed on either or both ends of the BPEs. The ISM also had an effect to shift the potential of the cathodic and anodic poles in a closed bipolar system in which solutions for both poles were separated.

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10.

Patients with food allergies show mild or severe symptoms including anaphylaxis when they take allergenic substances in food. As a technique to detect food allergens, electrochemical biosensors expect to be developed because they have advantages in simplicity and cost effectiveness. When applying nanosheets as an electrode material, they tend to re-stack and generally align horizontally with respect to the current collector due to their highly anisotropic nature. Here, a vertically-aligned nanosheet electrode was fabricated for electrochemical biosensing of allergenic protein in food. As a nanosheet, two-dimensional titanium carbide, MXene, was selected because it has high electric conductivity and abundant surface functional groups. The vertically-aligned electrode showed higher current density and smaller difference between the oxidation potential and the reduction potential than horizontally-stacked electrode. Furthermore, using the prepared vertically aligned MXene, we examined the changes in the current response of the vertically aligned MXene to food allergen addition.

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11.

The rapid detection of elevated glucose levels after a meal is important for diabetes diagnosis and the assessment of health risks for nondiabetics. Battery-free flexible glucose sensors are a promising tool for intermittent or continuous monitoring with a relatively low burden on biological tissues and living bodies because they are lighter and more flexible than conventional battery-driven glucose sensors. However, existing battery-free glucose sensors are unsuitable for the practical detection of elevated glucose levels after a meal because of their long response time (> 1 h) and response fluctuation. Here, we present a battery-free flexible glucose sensor that integrates phenylboronic acid hydrogel with an inkjet-printed interdigitated capacitor. We achieved a quick response time of 5 min by using the interdigitated capacitor to detect the dielectric transition inside a 200-µm-thick layer of phenylboronic acid hydrogel. In addition, we demonstrated the passive transfer of sensing data and the detection of elevated glucose concentration in mouse serum within 5 min. The proposed approach enhances response speed and can extend the lifetime of wearable glucose sensors.

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12.

Exosomes or nano-sized extracellular vesicles in bio-fluids are emerging clinical tools; therefore, effective interface is a key to design exosome-based diagnostic and therapeutic platforms. In this study, we have developed peptide-functionalized nanowires as a biorecognition interface for capture and release of cancer-derived exosomes. A peptide binding to CD9, an exosome marker, was screened from EWI-2's amino acid sequence using peptide array technique. The screened peptide showed an affinity to CD9 surface protein, and preferentially bound to CD9 rather than other two well-known exosome membrane proteins (EpCAM and integrin beta 5). Due to a higher expression of CD9 in cancer exosomes than in healthy or normal exosomes, the screened peptide likely bound to cancer exosomes in comparison to healthy exosomes. Linkage of the screened peptide with a ZnO-binding sequence offered self-assembly modification of ZnO nanowire array within a microfluidic channel. The peptide functionalization significantly improved the exosome-capturing efficiency of the nanowires, and thus allowed the captured exosomes to be released from the nanowires by 1 M NaCl solution. This engineered surface would be beneficial to develop the controlled microfluidic platforms for exosome-based analytical and medical devices.

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特別講演1

The application of microfluidic disc shaped devices to biological sensing has been investigated. On these devices, solutions including samples are introduced and transported into microchannels by centrifugal force without using any pump and where micro analyses can be conducted. These powerful aspects of such devices have enabled them to be used for simple and high-throughput analyses. We have developed microfluidic disc shaped devices that can be used as a biosensor for various applications. Three applications are reported here: to single cell isolation and detection of a cell-specific gene, discrimination of an entrapped cell by staining, and high-throughput analyses based on the enzyme linked immunosorbent assay (ELISA). In this paper, we summarize the applications of biosensors performed on the devices such as gene analysis of isolated cells based on a specialized polymerase chain reaction (PCR), cell staining for nonadherent cells, and rapid ELISA.

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特別講演2

Stress is defined as the adaptive defense response against changes in the environment as the stress theory. The stress might be evaluated by measuring neurotransmitters in the brain and blood stress hormones. The invasive sampling becomes a very large stress stimuli, and therefore, accurate stress cannot be evaluated especially for healthy persons. Saliva has been attracting attention as an alternative blood sample. The science of saliva secretion mechanisms for the stress defense response as well as the R&D on measurement tool can be visualized for the stress biological response. Using advanced biosensor & biochip technologies, we have made several R&D on single drop analysis for saliva stress marker candidates for ergonomics and clinical research field for 20 years. Here, we will introduce research strategy and results on some topics of the prototype of biosensor and microfluidics among the R&D.

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13.

The ability of a semiconductor gas sensor to detect gas-phase chemicals depends on the interaction of gas molecules with the sensing layer surface. Hence, optimizing the material structure is important to maximize the amount of adsorbed oxygen, gas diffusivity, and reactivity with gas. In this study, we focused on ZnO nanorods as n-type semiconductor materials for the detection of volatile organic molecules (VOCs). ZnO nanorod arrays were vertically grown on a substrate under hydrothermal conditions using ZnO nanocrystals, which were synthesized by a hot soap method, as seed crystals. The synthesized ZnO nanorods showed an extremely high response to acetone and ethanol even under humid conditions. The reason for the high response is due to the improvement of gas diffusion in the sensing layer and the effective formation of electron depletion layers over the ZnO nanorod surface.

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14.

In this study, we propose gas discrimination by a single semiconductor gas sensor based on novel heater-voltage modulation for realizing a compact and low-power consumption electronic nose. The modulation signal in which amplitude and frequency were periodically varied was use. Thereby, the sensor conductance was measured under exposure to ethanol, acetone, and butyl acetate with various concentration. Based on analysis by PCA and the discrimination model by k-NN method, the discrimination accuracy achieved to be 100 %, which was sufficiently higher than that by sinusoidal heater signal. As a result, the promising properties of the proposed modulation technique was demonstrated.

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15.

A novel catalytic combustion-type methane gas sensor was devised by applying the 11.3wt%PdO / 20wt%Gd₁₀Si₆O₂₇ /γ-Al₂O₃ catalyst possessing the high CH₄ oxidation activity of which can completely oxidize CH₄ as low as 300°C. The present sensor applying the 11.3wt%PdO / 20wt%Gd₁₀Si₆O₂₇ /γ-Al₂O₃ catalyst exhibited the quantitative response to CH₄ with linear relationship between the sensor output and the CH₄ gas concentration at 290°C with the 50% response time of 4−16 s.

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16.

Nitrogen monoxide (NO) contained in exhaled breath is a marker of asthma, and it is used in medical institutions worldwide as a test method for confirming the diagnosis and treatment effect of asthma. We developed a NOx detection chip (i.e., NO/NO₂ conversion chips and NO₂ detection chips), in which a porous glass substrate was impregnated with NO or nitrogen dioxide (NO₂) detection reagents, and have devised a simple analysis method for NO. In this study, the NOx detection chip was combined with an active method to measure low concentrations of NO within 30 min. The NO/NO₂ conversion chip had a NO conversion rate of 64% at a flow rate of 0.05 L min1, and the converted NO₂ reacted in the NO₂ detection chip. There was a linear relationship between the change in absorbance at 525 nm of the NO₂ detection chip and the NO concentration in the range of 10 – 205 ppb, with a maximum error of ± 22 ppb. In addition, it was found that the amount of change in absorbance at 525 nm of the NO₂ detection chip was not affected by flow rate and was constant in the range of 0.05 – 0.50L min^-1.

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