Vol. 41, Supplement A (2025)

清山賞受賞講演

Microfluidic rapid sensing technology addresses the limitations of traditional sensing methods, which require large equipment and are time-consuming. This innovation is gaining attention in biomedical and environmental monitoring fields. In medical diagnostics, ultra-fast PCR technology proved its efficacy during the COVID-19 pandemic, completing 40 cycles in just five minutes and enabling rapid anthrax detection. Additionally, Smart ELISA combines the high detection performance of ELISA with the simplicity of immunochromatographic methods, completing tests within 5 to 20 minutes. It has shown high performance in detecting SARS-CoV-2 neutralizing antibodies and food allergens. Industrial applications must meet regulatory "analytical validity" and gain approval from the Ministry of Health, Labour and Welfare. In the realm of industrial applications, it's imperative to foster collaboration with industry partners to effectively implement these technologies.

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1.

Sweats contain various organic substances involved in the metabolism of organisms. A typical indicator is lactic acid. As it is secreted in sweat during sustained high-intensity exercise, real-time monitoring can help recognize the degree of physical fatigue and prevent overwork. Because electrolytes are present in sweat, they are an effective target for electrochemical measurements. Furthermore, because the electrode itself does not need to be injected into the human body as a microneedle, it is a noninvasive measurement method that is less burdensome for the user. I In this study, we combined the electrochemical measurement of sweat with elemental analysis and conducted a study to better understand the electrochemical measurement of sweat. The two sweat analysis methods were performed in real time using a sweat collection microfluidic channel connected to an elemental analyzer and a flow system electrode for sweat analysis.

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2.

This study presents a histamine sensor chip utilizing molecularly imprinted carbon paste (MIP-CP) for real sample measurements. Histamine, a biogenic amine found in fish, can cause food poisoning if its concentration exceeds safe limits. Conventional methods such as immunoassays and enzyme-based techniques are time-consuming and impractical for real-time monitoring in fish processing. Therefore, this research aims to develop a disposable sensor for rapid and simple histamine detection. The sensor was fabricated by grafting molecularly imprinted polymers onto graphite particles using radical polymerization. These particles were mixed with silicone oil to form MIP-CP, which was applied to a disposable electrode structure. The sensor was tested using minced bigeye tuna spiked with histamine, and cyclic voltammetry was performed to establish a calibration curve. Additionally, histamine concentration in naturally stored tuna samples was measured and compared with a commercial enzymatic kit. The results showed that the sensor's readings closely matched those obtained using the enzymatic method. While the commercial kit required approximately 30 minutes for analysis, the MIP-CP-based sensor provided results in under 60 seconds. These findings demonstrate the sensor’s potential for fast and efficient histamine detection in fish products, supporting food safety and quality control efforts.

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3.

This study presents the development of a disposable molecularly imprinted carbon paste (MIP-CP) sensor chip for measuring vancomycin (VCM) concentration in human serum. Antibiotic resistance is a global issue, and precise therapeutic drug monitoring (TDM) is essential to ensure effective treatment while avoiding toxicity. However, conventional TDM tools are expensive, limiting their accessibility in developing countries. To address this, a sensor was fabricated using MIP-CP, where graphite particles were coated with a polymer imprinted with VCM. The sensor was tested using differential pulse voltammetry on human serum samples, showing stable calibration curves when a portion of the electrode wiring was replaced with Ag/AgCl ink. Compared to carbon-only wiring, this modification improved measurement stability over three months. The results demonstrate the feasibility of this sensor for rapid and cost-effective VCM monitoring, potentially enhancing antibiotic management in clinical settings, particularly in resource-limited regions.

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4.

Chiral analysis techniques are crucial for pharmaceutical development and metabolic research. To date, various chiral recognition materials have been developed considering complementarity with analytes, whereas the practical implementation of chiral sensors has often been hindered by synthetic efforts. Molecular imprinting methods stand out as promising techniques for obtaining three-dimensional recognition scaffolds allowing selective detection of specific analytes. In particular, molecularly imprinted polymers (MIPs) can be easily fabricated on solid substrates using electrochemical methods, which allow the construction of chiral cavities with minimal synthetic effort. In this study, we employed a solution-processable organic field-effect transistor (OFET) as a chiral sensor platform owing to its switching property. In this regard, an extended-gate structure was selected as the sensor structure to detect a chiral amino acid (i.e., L-histidine) in aqueous media. The MIP layer was electrochemically polymerized using a monomer in the presence of templet (i.e., L-histidine). The molar ratio of the monomer and the template was optimized by density functional theory calculations. The MIP-attached OFET selectively detected the target chiral analyte and displayed quantitative responses correlated with changes in the enantiomeric excess of L-histidine

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5.

This study presents a novel genosensor based on magnetic bimetallic-organic frameworks (MBOF) for detecting oncogenic miRNAs, specifically miRNA-21 and miRNA-3960. The synthesis approach emphasizes environmental sustainability via a simple electrochemical method by using recyclable zinc electrodes, non-toxic materials, and mild reaction conditions. The presence of zinc and copper ions in the framework was verified using Anodic Stripping Voltammetry (ASV) and ICP-AES, while structural properties were characterized using TEM, FESEM, EDS, and XRD. The sensor was modified with toluidine blue to improve conductivity and eliminate the need for enzyme-labeled probes, simplifying the design. The MBOF-based sensor achieves high sensitivity and selectivity for miRNA detection in complex biological samples with a dual-mode detection via square wave voltammetry and electrochemical impedance spectroscopy, providing a robust platform for point-of-care diagnostics and environmental RNA/DNA monitoring.

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6.

Beta lactam antibiotics are a diverse group of antimicrobial agents. Taste sensors with lipid/polymer membranes have been utilized as a method to evaluate the taste of pharmaceuticals. For example, BT0, a commercially available bitterness sensor for pharmaceuticals, has demonstrated the ability to detect bitter compounds such as quinine hydrochloride. However, it showed limited sensitivity to non-charged bitter substances. Novel taste sensors utilizing surface modification methods have demonstrated the capability to detect non-charged bitter substances, including caffeine. In this study, referencing the surface modification approach, the authors develop a taste sensor with 3-bromo-2,6-dihydroxybenzoic acid, enabling it to detect beta lactam antibiotics such as amoxicillin and cefalexin. The results of concentration-dependent detection demonstrated the feasibility of using the sensor for detecting amoxicillin and cefalexin.

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7.

Identification of pathogenic microorganisms is essential in food manufacturing and clinical settings. The conventional method relies on expert observation of culture plates, which is labor-intensive and subjective. To improve efficiency and accuracy, we developed a color colony fingerprint (CFP) system, integrating high-resolution imaging and machine learning for bacterial species identification.　The system successfully captured colony color information, which was previously unavailable in CFP imaging system. Evaluation using 13 bacterial species demonstrated that classification accuracy increased with colony growth, reaching 98.0% accuracy at 7.0 mm². Notably, several species with closely related appearances, such as Klebsiella and Enterobacter species, as well as Bacillus cereus and Bacillus thuringiensis, were distinguished with high accuracy. These results indicate that the color CFP method enables high-accuracy, automated bacterial identification, reducing reliance on expert analysis.

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8.

Gene delivery methods, which are commonly used for genome editing, include viral vector delivery and electroporation. However, these approaches present several challenges, such as limitations on the types of substances to be introduced and high cellular invasiveness due to electrical stress. To enable more efficient and versatile genome editing, there is a strong need for injection techniques that minimize cellular damage while allowing the delivery of a broad range of substances. In this study, we aimed to establish an injection method utilizing a nanopipette controlled by electroosmotic flow to facilitate efficient genome editing. As a preliminary investigation, we introduced polysaccharides, proteins, and DNA into human cell lines and assessed the feasibility of applying the nanopipette technique to mammalian cells.

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9.

Dielectrophoresis (DEP) enables label-free cell separation based on electrical properties. However, it is hard to separate cells with similar dielectric properties. To address this, we modified non-B cells with antibody-coated magnetic beads to alter their electrical properties, facilitating DEP-based separation and arraying B cells. Non-B cells in suspensions of mouse spleen cells were conjugated to anti-CD43 magnetic beads. The cells were resuspended in a sucrose-PB solution and introduced into a microwell device with an applied AC voltage (20 Vpp). B cells exhibited positive DEP (p-DEP) at ≥570 kHz and negative DEP (n-DEP) at ≤420 kHz, while modified cells exhibited p-DEP at ≥800 kHz and n-DEP at ≤500 kHz. Application of 700 kHz to a mixed cell suspension allowed to capture B cells selectively. After 10 minutes, 70% of the wells contained B cells. Immunofluorescence analysis confirmed that over 90% of the captured cells were B cells. This method allows efficient B cell isolation without labelling, supporting further applications such as hybridoma production.

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10.

We developed a microdialysis-integrated HPLC system with a dual-electrode detector utilizing track-etched membrane electrodes (TEMEs) for in vivo dopamine (DA) monitoring. The high electrolysis efficiency of TEMEs enabled calibration-free coulometric detection, simplifying quantitative analysis by directly determining DA recovery through a dialysis probe. This system was applied to real-time DA monitoring in the right striatum of a mouse brain. Following probe implantation, DA levels exhibited an initial exponential decay, likely due to tissue damage and neurotransmitter diffusion. Stimulation with a high-potassium solution induced significant DA release, validating the system’s responsiveness to neurochemical changes. Additionally, intraperitoneal administration of mirtazapine did not elevate DA levels in the right dorsal striatum, suggesting no acute dopaminergic activation. The dual-electrode detector enhanced DA peak identification by leveraging anodic and cathodic peak pairs, indicative of DA’s reversible redox behavior. The consistency between DA recovery from standard solutions and brain dialysate confirmed minimal interference from electroactive substances, ensuring high analytical reliability. By enabling continuous and selective in vivo DA monitoring, this system provides a robust tool for neurochemical investigations. The integration of microdialysis, capillary HPLC, and dual-electrode detection improves measurement accuracy, eliminates external calibration, and enhances peak identification. These advantages make the proposed method a valuable asset for studying neurotransmitter dynamics and their roles in neurological disorders.

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11.

Microbiological testing is an essential component of quality control in food and pharmaceutical manufacturing. Conventional culture-based methods require extended incubation time to obtain results. This delay prevents manufacturers from shipping their products promptly, leaving to challenges in inventory management and opportunity losses. To address these limitations, there is a need for rapid and user-friendly microbial detection methods. In response to this need, we have developed a novel microbial testing system using signaling probe-based DNA microarray. This system enables efficient microbial gene detection without requiring specialized technical expertise, making it a promising solution for rapid microbiological testing. In this study, we have established a multiplex detection method for microorganisms associated with contamination incidents. Furthermore, we investigated the application of this method for microbial detection from beverage.

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12.

We prepared organic salts composed of terephthalic acid and n-alkylamines with alkyl chain lengths greater than 8 as scavengers for OH radical (·OH). Single crystal X-ray structural analysis revealed that the alkyl chains were arranged parallel to each other and the zero-dimensional voids were adjacent to terephthalate (TA). Due to the presence of the zero-dimensional voids, ·OH penetrated into the crystal and reacted with TA to form fluorescent hydroxyterephthalate (HTA), allowing OH to be detected. In addition, the organic salt nanocrystals were successfully immobilized uniformly on a membrane filter by a simple dipping and drying process. We have also demonstrated an application example in which the two-dimensional distribution of ·OH generated on the surface of titanium oxide photocatalysts is visualized using the organic salt-immobilized sheet.

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13.

Electrochemical gas sensors have several advantages over other types of sensors including their wide tunable target gases, high sensitivity, low cost, and easy fabrication. Other desirable requirements for gas sensors include chemical stability, high gas selectivity, and no temperature dependence. In particular, electrochemical gas sensors using solid electrolytes are promising technipue due to their simple detection mechanism and high gas selectivity. In this study, graphene oxide (GO), which is inexpensive and abundant in material, was adopted as this solid electrolyte. In addition, metal-organic frameworks (MOF) are attracting attention for their application to gas sensors because ligands, conductivity, charge transfer reactions, etc. can be freely designed by selecting organic cross-linked ligands and metal connection points. The purpose of this study is to develop a highly gas-selective electrochemical sensor that can operate at room temperature.

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14.

This study investigates the acid-base properties and adsorption characteristics related to receptor functions. By introducing the acidic oxide WO₃, the sensing response of SnO₂-based gas sensors was significantly enhanced, enabling the selective detection of ethanol and acetone at different operating temperatures. These findings highlight the importance of WO₃ loading, distribution, and dispersity in tailoring gas selectivity and sensitivity, providing critical insights for the design of highly sensitive SnO₂-based gas sensors.

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15.

Semiconductor gas sensors detect low-concentration gases using changes in electrical resistance caused by gas adsorption and reaction on the material surface. Although acetone detection using semiconductor gas sensors is a non-invasive way, accommodations of their high operating temperatures, low selectivity, and the elucidation of the sensing mechanism are the task. Since acetone adsorbs to Lewis acid sites, improving the detection performance is expected by increasing the number of Lewis acid sites on p-block metal oxides. In this study, we compare amorphous Ga-In-Sn-Zn oxide (GITZO) nanoparticles with amorphous In-Sn-Zn oxide (ITZO) nanoparticles, which we previously reported. GITZO was synthesized using the hot soap method. GITZO exhibited superior sensor sensitivity and gas selectivity compared to ITZO. This result suggests that an increase in Lewis acid sites contributes to the improvement of the sensor performance.

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16.

To identify the most suitable noble metal catalysts for propane detection at low concentrations, we evaluated catalytic combustion activity and sensor response to 20–100ppm propane using Pt-loaded SnO₂ (Pt/SnO₂) and Pd-loaded SnO₂ (Pd/SnO₂). No catalytic combustion was observed for neat-SnO₂ at 250°C, but increasing trend was noted about 300°C. The loading of Pt or Pd significantly enhanced catalytic combustion, with Pt exhibiting greater catalytic activity for propane combustion than Pd. Conversely, the sensor response of Pd/SnO₂ was higher than that of Pt/SnO₂. This opposite trend can be attributed to both the redox properties of Pd with PdOx and the combustion mechanism of PdOx which follows the Mars–van Krevelen mechanism. Consequently, Pd exhibited a strong electron sensitization effect on the SnO₂ sensor, making it a more effective catalyst for propane detection at low concentrations.

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