Vol. 39, Supplement B (2023)

17.

The investigation into SnO₂ rod-like particles (nanorods) aimed at enhancing sensor response to ethanol, as the impact of SnO₂ particle shape on Pd-loaded SnO₂ sensors had not been elucidated. In order to assess the influence of different SnO₂ particle shapes on the ethanol sensing properties of Pd-loaded SnO₂, SnO₂ nanoparticles (NPs) and nanorods (NRs) were employed. Through Ethanol-Temperature Programmed Reaction, it was observed that both Pd-loaded SnO₂ NPs and NRs exhibited heightened activity towards ethanol, although this effect was particularly pronounced for SnO₂ NPs. Further analysis using X-ray photoelectron spectroscopy indicated that Pd tended to exhibit a higher oxidation number on SnO₂ NPs compared to NRs, which could potentially contribute to the observed increase in activity.

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18.

Using Au-loaded SmFeO₃ p-type semiconductors, sensor responses to ethanol and toluene were investigated. 0.5wt% and 3.0wt% Au was loaded on the surface of SmFeO₃ by the impregnation method. Au was found to be homogeneously dispersed on the SmFeO₃ surface. Using 0, 0.5 and 3.0wt% Au-SmFeO₃, sensor responses to 1, 3, 5 ppm ethanol and toluene at 250℃ were investigated. Response to ethanol was significantly enhanced by the Au-load. On the other hand, the effect of Au-load on a response to toluene was negligible. The difference of sensor responses can be explained in terms of reactivity of ethanol and toluene on SmFeO₃. The VOCs adsorb on the Au particles to increase the surface VOC concentration, which may promote diffusion of VOCs in the electrode. The reaction of ethanol is diffusion controlled and shows high concentration dependence, whereas toluene has low reactivity on SmFeO₃ and is expected to have little concentration dependence.

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Microparticles dielectric materials polarized in an electric field to induce a dipole moment. In the rotational electric field, the microparticles were rotated by the interaction, between the induced dipole moment and the rotational electric field. This phenomenon is called electrorotation. The rotational rate depends on the surface conductivity of the dielectric material. In this presentation, we evaluated the rotation rates of microrods modified with peptide nucleic acids (PNA) that was used as a recognition element. The rotation rate of microrods modified with DNA decreased, compared to the microrods without modification, while the rate of the microrods modified with PNA almost correspond to the original rate. The result indicated that the induction of the negative charge to the surface led to the decrease of rotation rate. Furthermore, the rotation rate decreased when the PNA modified microrods were treated with complementary DNA, while the rotation rate is constant after treating with non-complementary DNA. Thus, the use of the rotation rate as a signal output would allow to, developing the non-labeling detection method for complementary DNA.

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20.

The non-enzymatic glucose sensor has the advantages that it can be used in an environment different from in vivo and that it can be easily extended its life by regeneration of the surface by an appropriate treatment. On the other hand, substrate specificity is often inferior to enzymatic sensors. In our previous study, an electrochemical sensing of glucose with a mesoporous platinum which has a lot of high index surface, is shown to exhibit not only high sensitivity but also selectivity against interferents such as ascorbic acid and acetoamidophenol, in an alkaline solution. In this study, the glucose sensing performances of the electrode in human serum solutions were investigated. As a result, glucose oxidation peak current density linearly increases with the concentration in diluted solutions of human serum at a concentration between about 0.1 and 0.5 mM of glucose. However, the peak current density decreased nearly to zero after multiple uses of the electrode, and the active surface area of the Pt was decreased at the same time. Alternatively, it was confirmed that peak current density remains after several measurements as the film thickness of the mesoporous Pt increases, and as the dilution ratio of the human serum increases. The regeneration of the electrodes is considered to be a next issue.

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21.

In the course of our research for enzyme biosensors, we considered the possibility that the activity of enzymes may change under an electric field due to their structural characteristics. One of the structural features of enzymes is that the protein that structures the enzyme is charged. Another feature is that the active center is composed of metal ions and organic substances. In this study, we compared the enzyme activity under electric and non-electric fields to verify the above hypothesis. The results suggest that the enzymatic reaction was activated when glucose dehydrogenase, which was used as a model enzyme, was exposed to a negative electric potential. In this study, the activity of the enzyme reaction was confirmed in the range of -0.3 V to -0.1 V. The possible reasons for this are the charge of the protein and the involvement of Ca²⁺, a metal ion, in the active center of glucose dehydrogenase.

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22.

In recent years, there has been a growing demand for RNA detection methods in the diagnosis of cancer and viral infections. In particular, amperometric sensors are expected to be a quick and simple biosensing device. In this study, we attempted to apply the signal amplification by a ternary initiation complex (SATIC) to amperometric sensor for the RNA detection. As a result, reduction current of hydrogen peroxide was specifically increased in the presence of target RNA by the amplification of DNAzyme strand, which has peroxidase-mimicking activity. Furthermore, amperometric sensors with SATIC system were enabled to quantitatively detect RNA in the range of 1 pM to 1 nM.

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清山賞受賞講演2

This article reviews our achievements of cell-based biosensors for the detection of low molecular weight compounds. Two topics are presented in this review. First, the development of artificial cells expressing olfactory receptors, chimeric G-proteins, and potassium ion channels for sensing low molecular compounds is presented. Furthermore, in order to detect various types of VOCs, we developed comprehensive screening of olfactory receptors that bind to the target VOCs using olfactory sensory neuron arrays. Finally, we introduce simultaneous and non-invasive single-cell analysis microelectrode devices based on electrorotation. These innovative microelectrode devices have the potential to pioneer cell-based biosensors for the detection of low molecular compounds such as odorants and VOCs.

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特別講演

Miniaturization of sensing devices is required in various fields such as clinical analysis, environmental monitoring, food science, and cell engineering. Depending on the situation, miniaturized sensing devices are desired. To this end, various bio/chemical sensing devices have been developed by semiconductor and MEMS related microfabrication techniques. Not only independent microsensors but also devices with integrated sensors were fabricated including those based on bipolar electrochemistry. Furthermore, electrochemical sensors were coupled with microfluidics aiming for efficient on-chip solution processing. Trials to realize autonomous solution processing have also been made. In addition, auxiliary techniques were developed to realize highly functional devices. These include switchable hydrophobic valves, a pH-stat, and metal connections as alternatives to liquid junctions. In this presentation, our trials to realize microfabricated electrochemical sensing devices will be introduced.

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23.

The incidence of hyperuricemia, which causes pain syndrome and nephritis, is becoming a serious problem due to the increasing age of onset at younger ages. Therefore, we believe that there is a need for a measurement device that is closely related to daily life and can be easily used at home or in the workplace. Therefore, the purpose of this study is to develop a uric acid biosensor that is easy to operate, selective, and accurate like blood glucose level sensors that are already in widespread use. In this study, we focused on ascorbic acid as a foreign substance. The oxidation potential of ascorbic acid is similar to that of uric acid. In this study, we decided to use the double pulse potential step (DPPS) method, which is one of the electrochemical methods, to measure uric acid with high accuracy.

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24.

Reactive oxygen species (ROS), when generated in excess, cause serious diseases such as cancer and lifestyle-related diseases. Among them, superoxide (O₂ ^−•) is a precursor of ROS with high oxidative capacity, and quantitative measurement of O₂ ^−• is important for preventive medicine. In our group, we have developed an electrode modified with an iron porphyrin complex for the quantitative measurement of O₂ ^−•. In this study, in order to investigate the effect of the number of thienyl groups on the current response, electrodes modified with iron porphyrins (trisubstituted), in which three of the four meso-substituted groups are thienyl groups and the remaining one is ethyl group, were prepared and the current response to O₂ ^−• was examined. Compared to the tetrasubstituted and monosubstituted modified electrodes in previous studies, the current response to O₂ ^−•/ was evaluated, and the results showed that the response of the trisubstituted electrode was comparable to that of the tetrasubstituted electrode. It is suggested that this difference in responsiveness may be related to the membrane structure.

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25.

Salivary cortisol is often used as a biomarker of psychological stress and disorder. In this study, we employed a molecularly imprinted polymer (MIP) as the detection scaffold for the chemical sensing of cortisol in human saliva. The MIP optimized by density functional theory (DFT) possesses a three-dimensional recognition network through hydrogen bonds, which was combined with an extended-gate-type organic field-effect transistor (MIP-OFET). The MIP-OFET sensor exhibited a sensitive response to cortisol with a limit of detection of 0.72 µg/L, indicating the applicability of the MIP-OFET to the quantification of salivary cortisol. Moreover, the selectivity test of MIP-OFET over similar steroids (i.e., progesterone and prednisolone) and interferents in human saliva showed a highly selective response to cortisol. Importantly, the spike-and-recovery test results for cortisol in human saliva demonstrated the potential of MIP-OFET as a diagnostic tool for salivary cortisol levels, given its precise recovery rate of 102-110%.

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26.

5-Fluorouracil (5-FU) is widely used for cancer treatment because it is an effective and inexpensive anticancer agent for various cancers. However, as there are large individual differences in efficacy and side effects due to resolution in the liver, few patients are administered within the optimal blood concentration range for cancer treatment. In this study, we demonstrated the detection of 5-FU using a field effect transistor (FET) biosensor with competitive method. Voltage shifts in transistor characteristics were obtained due to the adsorption of unbound antigen binding fragment (Fab) remaining after mixing with target 5-FU on 5-Fluorouracil acetate (FUAc)-immobilized FET surface. As a result, the sensor responses derived from negative charges of Fab molecules were decreased depending on the 5-FU concentrations in buffer solution. Therefore, the FET biosensor system with competitive method was expected to lead the monitoring the 5-FU dosage.

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27.

We have developed a novel electrochemical imaging method using a closed bipolar electrode (cBPE) array coupled with electrochemiluminescence (ECL) named “bipolar elec-trochemical microscopy (BEM)". In this study, we investigated a low-cost and easy method to fabricate a cBPE array generating uniform ECL. First, we employed a method (PPP method) in which conducting carbon paste is applied to the pores of the track-etched mem-brane with 8-µm pore diameter by applying 20 MPa using a desktop press. From almost all the points ECL was observed after one-time filling of carbon paste with PPP method, but after two-times filling, the ECL was disappeared. This disappearance is because air was sandwiched between the carbon filled in the first and second times. From this result, "one-time filling by PPP method" was confirmed to be useful. PPP method was also applied to track-etched membrane with pore diameters of ~0.6 µm, but the locations and timing of ECL were non-uniform. For uniform light emission, densely filling of the paste without air containing to the pores might be important.

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28.

Histamine (Hm) contamination in histidine-rich foods poses a significant food safety challenge. Current detection methods rely on complex and costly immunoassays, limiting accessibility and efficiency, especially in regions with high raw fish consumption. This study introduces an innovative histamine detection approach to overcome the limitations of current methods. A disposable electrochemical sensor chip was made using molecularly imprinted polymers (MIPs) on a polyethylene terephthalate (PET) substrate. The sensor incorporated molecularly imprinted carbon paste with redox monomers (vinyl ferrocene or allylaminocarbonylpropionic-3-ferrocene), eliminating the need for external reagents. The MIPs were grafted onto graphite particles via radical polymerization. Cyclic voltammetry was used to accurately measure Hm concentrations. The sensor exhibited notable sensitivity and a strong linear relationship with histamine concentrations. High selectivity against histidine was demonstrated. The results show that this sensor has the potential to significantly improve the real-time detection of histamine.

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29.

We have recently proposed and examined surface plasmon-enhanced fluorescence (SPEF) imaging based on the surface plasmon resonance (SPR) sensor principle. The resonant excitation of SPR provided an enhanced intensity of the electromagnetic field, which was directly translated to an increased SPEF intensity of fluorescent probe (FITC-BSA membrane, Calcein-AM in RBL-2H3 cells, and ruthenium complex (Ru(phen)3) in Nafion membrane) at the surface of sensor chip by using laser diode (LD) or LED as a short wavelength light source. In this study, an EMCCD camera was used to demonstrate the above approach for detection of SPEF signal and SPEF imaging, and a long-range SPR (LRSPR) sensor chip was used to enhance SPEF intensity. As a results, it was found that our SPR-SPEF imaging system could be captured SPEF images of FITC in FITC-BSA membrane, Calcein in RBL-2H3 cells, and Ru(phen)₃ in Nafion membrane for sensing of dissolved oxygen.

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30.

Temperature and oscillation frequency directly affect the dynamics of soft matters under dynamic-mechanical conditions. Namely, temperature influences stiffness, and oscillation frequency changes the molecular response region. In MHz-oscillating region, the resonant length of a soft matter, which means the molecular length moving with an oscillating solid-liquid interface, shows the dynamics of its main chain. Here, we investigated the dynamics of a linear soft matter against temperature and oscillating frequency. The examination was carried out using a quartz crystal microbalance (QCM) with a chemisorbed soft matter. As a soft matter, the self-assembled monolayers (SAMs) formed from six types of mercapto oligo(ethylene oxide) methyl ethers were employed. The novel analysis based on the Debye process has revealed that the logarithmic value of the resonant length linearly decreased with that of the QCM angular frequency in the present temperature range and converged into the single point independent of temperature. Especially, the evaluation from the point of the resonant molecular weight led to the appearance of the convergence point independent of chemisorption, physisorption, molecular conformation, and temperature.

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