Vol. 31, Supplement B (2015)

1.

We have developed non-enzymatic glucose oxidation electrode composed of electrolytic manganese dioxide (EMD). By using the EMD modified electrode, glucose is electrochemically oxidized in analyte with near neutral pH (pH 8.0) due to its electrocatalytic ability. In order to study its detailed electrochemical properties, effects of temperature and pH of analyte on the glucose oxidation were investigated for an application to glucose sensor. Furthermore, we also prepared polyion complex (PIC)-coated EMD electrode to improve electrochemical stability and sensitivity for detecting glucose. From these results, we will discuss detailed mechanism of glucose oxidation at EMD modified electrode.

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2.

Glucose oxidase (GOx) and Horseradish Peroxidase (HRP) were physically adsorbed onto porous carbon felt (CF), which is a microelectrode ensemble of micro-carbon fiber and possesses a three-dimensional random structure. HRP and thionine (TN) were firstly adsorbed onto the CF, and then, the GOx was further adsorbed onto HRP/TN-adsorbed CF (step-wise adsorption). The resulting GOx/HRP/TN-adsorbed-CF was successfully used as an amperometric detector for FIA-type biosensor for glucose. Enzyme-adsorption conditions and operational conditions were optimized. The developed biosensor showed the sensitivity (2.076 μA/mM), the limit of detection (0.014 mM), and linear range (0.03 ～ 3 mM). Interference by ascorbic acid was able to cancel by the control of applied potential. The RSD for 63 consecutive injection of 10 mM glucose was 3.71 %. The resulting GOx/HRP/TN-CF-based FIA biosensor was applied for the determination glucose in various beverages, and the analytical results obtained by the sensor was fairly good agreement with those by the conventional spectrophotometry.

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3.

A fine needle type glucose sensor, which has sensing region on the tip of a fine tapered electrode, was prepared using tapered PEEK tube with platinum-iridium alloy wire. Glucose oxidase was immobilized on the surface of Pt-Ir electrode using the combination of electrodeposition and electropolymerization procedures. The obtained sensor showed good response with sufficient linear relationship between response current and glucose concentration. Long-term stability of the obtained electrode was evaluated for 35 days. After initial change of response current for a week, constant response current was obtained for 1 month and approximately 80% of the initial sensor response remained. In vivo measurement evaluation of the electrode was performed using rabbit. Considerable glucose sensor response change due to the trend of glucose concentration was observed.

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4.

Alzheimer's disease ( AD ) is one of the type of dementia. -Secretase is known as one of a key enzyme for development of therapeutic agent to AD because the amyloid plaque causing AD was produced by the catalysis of the enzymes. Several inhibitors to -secretase was known and the effects of the inhibitors are also known as a reversible and competitive inhibitors. In the previous study, we already developed the system to evaluate properties of the inhibitors whether its effect is reversible or irreversible. In this study, we developed evaluation system for activity of -secretase by using immobilized recombinant -secretase in combination with a FIA (Flow Injection Analysis) system. On the other hand, conventional method for enzyme immobilization cannot control enzyme orientation. Hence we investigated orientation of immobilized enzyme by using specific binding of biotin and streptavidin. And also we tried to miniaturize to system for minimize of material and reduce assay time by micro flow channel.

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5.

A carbon screen–printed disposable microchip as a microstructured two-electrode system was used for the establishment of a chronoamperometric total antioxidant capacity (C-TAC) assay of foods and drinks. The electrochemical response to an antioxidant was indirectly determined through mediator, and was strongly affected by the solubility of both the mediator and the antioxidant in the measurement solution. By intensive investigation, it was found that methanol was the best solvent for the measurements and food extraction. Under optimum conditions for the C-TAC assay, micro-volume measurement of 30 µL was realized using the present microchip, and calibration curves for representative antioxidants were successfully obtained with excellent determination coefficients. Finally, the conventional DPPH test using foods and drinks was applied for comparison with the present C-TAC method, and the obtained results showed good correspondence.

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6.

Currently, vancomycin is primarily used to treat serious infections caused by gram-positive bacteria which are known or suspected to be resistant to other antibiotics. But vancomycin has a serious nephrotoxicity, and then the monitoring of the level of vancomycin in serum is most strongly proposed. The purpose of the present study is a development of reagentless sensor for monitoring vancomycin using molecularly imprinted polymer. Vinylferrocene, methacrylic acid, acrylamide and methylenebisacrylamide were copolymerized with grafting onto indium-tin oxide (ITO) electrode in the presence of vancomycin as a template. Differential pulse voltammetry was performed with the grafted electrode in buffered saline solution. The current at 0.8 V vs. Ag/AgCl was sensitive to the vancomycin concentration between 0-50 µM however was unstably sensitive to teicoplanin which has similar structure to vancomycin. The electrode prepared without template (non-imprinted electrode) was insensitive to vancomycin. As a result, an electrode grafted with vancomycin-imprinted polymer including ferrocenyl group can work as a reagentless sensor for vancomycin. It would be helpful for monitoring of vancomycin.

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7.

A real-time heparin sensor is required to optimize dosage of heparin for extracorporeal circulation and its antidote protamine. Then, we are trying to develop a heparin sensor using a molecularly imprinted polymer (MIP). In the present work, we studied the method to stabilize measurement of heparin concentration in whole blood by using the MIP-grafted electrode. An initiator of radical polymerization was introduced on an indium-tin oxide (ITO) electrode. Heparin sodium, methacryloxethyltrimethoxysilane, and acrylamide were dissolved in water. Methylenebisacrylamide was dissolved in dimethylformamide. Mixture of the both of the solutions was introduced into the gap between the surfaces of quartz crystal plate and the treated ITO electrode. Ultraviolet was irradiated to the surface of the ITO to graft copolymer of the monomers. The ITO was washed with aqueous solution of 1 M sodium chloride to remove the template and to obtain the MIP-grafted electrode. Cyclic voltammetry was performed with the MIP-grafted electrode in physiological saline or bovine whole blood including 0-8 unit/mL heparin and 5 mM ferrocyanide as a redox marker. As the result, the current intensity was decreased by the increase of heparin concentration either in the saline or the whole blood. However, the sensitivity to heparin in the blood was approximately 50% of that in the saline. The heparin-sensitivity of the electrode coated with SEC-1® (Toyobo) in the blood was 74% of that in saline. As another approach, uncoated-electrode was washed at the interval of measurement in blood with protease-containing detergent. The heparin-sensitivity in the blood with the washed electrode was 77% of that in the saline.

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8.

We developed an absolute determination method of residual chlorine using an electrolytic modified carbon felt (EMCF) electrode as a working electrode. The EMCF electrode was fabricated by stepwise electrolysis in ammonium carbamate solution and sulfuric acid. The electrochemical behavior of the EMCF electrode was measured by using cyclic voltammetry. The reduction wave of residual chlorine began from 0.8 V vs. Ag/AgCl in a neutral medium. A good linear relationship was obtained in the concentration range of 0.13 to 788,000 mg L-1 Cl residual chlorine. The relative standard deviation for tenth successive measurements was less than 1.3 % for 130 mg L-1 Cl. The measurement of residual chlorine was finished completely in a short time(~60 sec.). The electrical charge obtained by measurement of residual chlorine was not dependent on the pH region from 2 to 8. This indicated that our proposed method can be used for the measurement of the residual chlorine concentration.

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清山賞受賞講演1

Our recent developments of fiber-optic hydrogen gas sensors based on evanescent-wave absorption and Bragg wavelength shift are introduced. A platinum-loaded tungsten trioxide (Pt/WO₃) thin film as a hydrogen sensitive material for the evanescent-wave type sensor was successfully immobilized on the periphery of optical fiber core by sol-gel method. The sensor could respond to hydrogen gas and the reproducibility was good. A distributed sensing performance using optical time domain reflectometry were demonstrated. Secondary, the fiber-Bragg grating (FBG) hydrogen gas sensor based on catalytic-heat is described. The sensor device where a platinum-loaded silica (Pt/SiO₂) film was immobilized on the periphery of the FBG portion exhibited rapid response. These sensor devices would have a great potential for applying to distributed monitoring of hydrogen leakage from equipment related to hydrogen energy system.

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清山賞受賞講演2

Electrical and electrochemical sensing systems have been employed in biosensors due to the ease of integration of electrodes and control circuits on the miniaturized devices.　In contrast, usage of photo-sensing systems developed with advanced optical components (e.g., condensing lenses and optical filters) has been hampered duet to the difficulties in miniaturization and cost-cutting. However, recently, those limitations are going to be overcome owing to the diffusion of digital cameras and cell phone, in which two-dimensional (2D) photosensors are equipped as imaging devices. Consequently, novel biosensors using 2D photosensors with microfabrication and microfluidic technologies are emerging. Those sensors are free from bulky optical systems (e.g., objective lenses), instead, improve light condensing efficiency on the photosensors to complement low detection sensitivity. Those technologies can contribute to miniaturization of photosensing-based biosensors. In this article, biosensing technologies using 2D photosensors for single-nucleotide polymorphism (SNP) detection based on DNA microarray and cell analysis are introduced.

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9.

We have recently developed an electrochemical endotoxin (ET) detection system by using a combination of an ET-affinity microparticle (CellufineTM ETclean), a zinc complex-based probe for ET detection (ET probe), and an ultraflat nanocarbon film electrode. We have used cetylpyridinium molecule as an ET recognizing part of the ET probe and achieved highly sensitive ET detection (LOD=0.2 ng/mL) by the anodic stripping voltammetry of zinc ion from the captured ET probes. In this report, we applied the already reported ET recognizing peptides (Li5-025 and Sushi peptide) for this ET detection system. We have confirmed ET-affinity of these peptides by surface plasmon resonance measurement. The poly-ε-lysine modified sensor chip captured ET molecules in sample solution and the peptides recognized the adsorbed ETs. However, it was found that ET probes containing these peptides tended to adsorb non-specifically to the poly-ε-lysine membrane and the surface of ETclean microparticle, and therefore, high background signal (noise) was observed. We used the detergent (Tween20) and blocking reagent in the measurement solution to reduce noise and achieved higher S/N ratio in the ET detection system.

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10.

Circulating tumor cells (CTCs) are defined as tumor cells circulating in the peripheral blood of patients with metastatic cancer. The number of CTCs has prognostic value in patients and can be used to evaluate therapeutic effects. Recently, we have developed a microcavity array (MCA) (6 mm × 6 mm, Hitachi Chemical Co. Ltd.) system for highly efficient enrichment of CTCs based on differences in cell size and deformability. However, microscopic scanning is required to observe the entire area of a MCA, resulting in lower throughput of image analysis. If the CTCs trapped on microfluidic devices are imaged by one-shot, rapid detection of CTCs is possible. In this study, a wide-field imaging system using two dimensional (2D) complementary metal oxide semiconductor (CMOS) photosensor was developed and combined with the microcavity array system.

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11.

A gold nanoantenna structure was used to enhance the electric field in a gap region between two connected gold nanorods (GNRs) for fluorescence analyses. The position and orientation of the GNRs could be controlled by taking advantage of the properties of crystal structure of the GNR and by solid phase synthesis to improve detection sensitivity of molecules for many biochemical analyses. To obtain nanoantenna structures consisting of GNRs of predetermined numbers, the GNRs were sequentially coupled to the growing GNR chain immobilized on microbeads, which was confirmed by SEM observation. Fluorescence from a dye in the gap of the nanoantenna was enhanced significantly even with weak excitation light compared with the vicinity of single GNRs.

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12.

To carry out research and development on new stress-sensing devices for stress science study, we have investigated several microfluidic POCT (point of care testing) systems and FET biosensors for measurement of salivary stress-marker candidates. During the fundamental studies on the prototype of stress-sensing devices, such as electrophoretic microfluidics and ISFETs (ion-selective field-effect transistors), for real salivary samples of healthy volunteers, we found salivary nitrate might be a biomarker candidate on the autonomic nervous system response to stress. To make a scientific study on the stress response mechanism of salivary nitrate, we investigated simultaneous monitoring for healthy volunteers on mental workload for events of a ship handling using wearable heart rate monitor and salivary nitrate sampling measurement by prototype of salivary nitrate checkers based on NO₃--ISFETs using direct potentiometry. We preliminary discussed the secretion mechanism of salivary nitrate for autonomic nerve system response to stress.

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13.

An amplification method for surface plasmon resonance (SPR) signal has been studied in this research. Since our target clenbuterol (CLB) is a small molecule, indirect competitive inhibition method is employed. However, the signal change was very small because this method monitored the initial process of immunoreaction. In order to enhance the signal change, a use of Au nanoparticle is devised in the sensing. As known, Au nanoparticle causes the further electromagnetic wave oscillation at the interface. It is so-called localized surface plasmon resonance (LSPR). In this study, we compared the sensing performance between the primary and the secondary antibody (Ab) labeled with 40 nm Au nanoparticle (NP). It was noticed that Au NP bonded to the primary Ab caused 400% signal amplification. Furthermore, the secondary Ab-Au conjugate provides tremendous signal amplification (1200%) and further improvement in the limit of detection of 29 fg/mL (ppq).

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14.

Environmental water such as moisture, mist, steam rain drops, etc gives critical effect on manufacturing of products, growing of plants, their logistics and storage, infrastructure corrosion, mold generation and so on. In order to develop environmental water sensor superior to conventional humidity sensors, a new sensor based on galvanic action, which electric current flows through the condensed water or dew as an electrolytic solution between different metals, was made by using a semiconductor microfabrication technology involving the photolithography, the metal deposition and the lift-off processes in this study. This sensor showed a high-speed response, high sensitivity and low power consumption.

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15.

We conducted a basic study to construct an arrayed amperometric measurement method using closed bipolar electrode system (cBPES). In a limiting cell and an excess cell of cBPES, 0.5 mM p-aminophenol (pAP) and 1 mM ferrocyanide /1 mM ferricyanide mixture solution were prepared, respectively. As a bipolar electrode, electrically connected two Au electrodes with 1.6 mm in diameter were inserted into each cell. A driving electrode in the excess cell was connected to a connector of a potentiostat for working electrode (WEc). Another driving electrode and an Ag/AgCl reference electrode in the limiting cell were connected to a connector for a counter (CEc) and a reference electrode, respectively. Using this cBPES, we obtained a cyclic voltammogram reflecting a redox reaction of pAP on the bipolar electrode. Next, we connected two cBPES in order to test a primitive arrayed cBPES. Even if two driving electrodes of two cBPES were connected each other with one electrical lead connected to the WEc, only pAP reaction proceeding in one cBPES was monitored. This indicates that by switching the driving electrode connected to the CEc, amperometric measurements in multiple cBPES can be performed with one electrical lead for WEc.

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16.

In recent years, it has been reported that apoptosis of cancer cells is induced by the inhibition of intracellular lactate dehydrogenase (LDH). Therefore, the development of rapid screening sensors for LDH inhibitors is required. Here, an electrochemical sensor which can quickly and easily evaluate the ability of a LDH inhibitor is proposed. LDH catalyzes the reduction of pyruvate to lactate in the presence of NADH in neutral pH solution. Then the consumption of NADH by this enzymatic reaction was measured by differential pulse voltammetry (DPV) with a glassy carbon disk electrode (GCE). The rate of enzymatic consumption for NADH was investigated in the presence and absence of oxamic acid, which was already known as a LDH inhibitor. The results suggested that the electrochemical enzyme sensor measurement was available to screen LDH inhibitors.

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17.

Immobilization of biocatalysts onto carbon fibers modifiedchemically was investigated. Each of a disk type of theimmobilized enzymes was applied to a flow sensor and then,the performance characteristics of the systems were performed.

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18.

Photoelectrochemical sensing has become a promising analytical tool for the detection of biomolecules owing to its high sensitivity with low background noise. The physiological glutathione concentrations are an excellent indicator of various disease risks. Here, we report Au nanoparticles decorated TiO₂ nanocomposites show higher sensitivity and selectivity towards glutathione detection by the unique catalytic activity of Au nanoparticles. Electrospun nanostrucure of Au-TiO₂ nanocomposites were coated on FTO substrates followed by annealing at 500C. Upon glutathione addition to phosphate buffer, significant increase in current density was observed for Au-TiO₂ electrode than without glutathione. The photocurrent response of Au-TiO₂ electrode shows selectivity towards glutathione over ascorbic acid and glucose at 0.33 V (vs. Ag/AgCl) than TiO2 electrodes. The Au-TiO₂ nanocomposite electrodes showed a higher sensitivity with linear range between 0.0125 mM and 0.5 mM, which can be ascribed to the higher catalytic activity and strong interactions of Au nanoparticles with glutathione.

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19.

Efficient bidirectional microfluidic transport was achieved through the reversible electrochemical production and shrinkage of hydrogen bubbles. A three-electrode system with a platinum black working electrode, a Ag/AgCl reference electrode, and a platinum auxiliary electrode was incorporated into a poly(dimethylsiloxane) structure with the flow channels and compartments. The influence of the electrode and flow channel structures on the operation of the system was investigated. The production and shrinkage of bubbles was achieved by applying appropriate potentials to the working electrode, which minimized the influence of spontaneous shrinkage resulting from the oxidizing effect of dissolved oxygen. Device performance depended on the structure of the working electrode, meaning that further optimization will be necessary. The device was shown to withdraw solution through a minimally invasive needle and to process liquid plugs in a microfluidic system.

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29.

Polymethylmethacrylate (PMMA) microspheres were synthesized in distilled water by ultrasonic-assisted emulsion polymerization. The morphology of PMMA microspheres obtained was relatively uniform and their sizes were controlled within a range of 28 nm to 70 nm by adjusting the additive amount of sodium lauryl sulfate into the emulsion. Porous In₂O₃ spherical particles (In₂O₃-p(d), d: the size of the PMMA microsphere (nm) used) were prepared by ultrasonic spray pyrolysis of In(NO₃)₃ aqueous solution containing the PMMA microspheres. The NO₂ response of the In₂O₃-p(d) sensors, which were fabricated by screen printing, increased with a decrease in the size of the PMMA microspheres at lower temperatures ( 250°C). In addition, reduction in the size of the PMMA microspheres accelerated the response speed of In₂O₃-p(d) sensors.

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30.

We examined the sensing behavior of metal-doped SnO₂ semiconductor gas sensors to ethanol. Metal-doped SnO₂ films were prepared from mixed solutions of Tin (Sn) and zinc (Zn) or lead (Pb) or titanium (Ti) or molybdenum (Mo) ICP standard solutions. The sensitivity of all fabricated metal-doped SnO₂ sensors, Sn/Zn=1, 2, Sn/Pb=1, 2, Ti/(Sn+Ti)=0, 0.01, 0.05, 0.1, 0.2, 0.4, 0.6, 1.0, Mo/(Sn+Mo)=0.01, 0.1, 0.2, 0.4, to 0.64ppm ethanol were higher than that of metal-doped SnO₂ gas sensors prepared from SnO₂ powders. The highest sensitivity was observed for the Sn/Zn=1 sensor at 700oC, 0%RH, but the sensitivity of the Zn-doped SnO₂ sensor decreased in humidified environment. Scanning electron microscopy (SEM) images show that films prepared from mixed solutions composed of fine particle.

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31.

We have investigated monitoring of lung cancer-related volatile organic compounds (VOCs) (nonanal, n-decane, and acetoin) and sugar diabetes-related VOCs (acetone and methyl i-butyl ketone) in simulated room air. We have used 300 ?g/m³ of 31 kinds of VOCs as simulated contaminated room air, as this has been proposed to resemble an indoor air-like gas. We have collected sensor signals from a sensor array comprising four commercially available sensors (Figaro TGS 2600, 2602, 2610, and 2620) and our laboratory-developed sensors (Pt, Pd, and Au loaded SnO₂ (Pt,Pd,Au/SnO₂)). The signals from sensors array have been analyzed using principal component analysis (PCA). It was found that the four TGS sensors were insufficient for discriminating VOC gases, whereas both TGS and Pt,Pd,Au/SnO2 sensors could successfully discriminate between lung cancer- and sugar diabetes-related VOCs in contaminated room air as well as synthetic clean air.

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32.

Acetaldehyde is produced in the body after drinking alcoholic beverages and is certified as an evident carcinogen of esophagus and head and neck. Acetaldehyde carcinogenicity caused by alcoholic beverages is associated with the genotype of ALDH₂ that eliminates acetaldehyde. Thus it is important to research the genotype from the aspect of Preemptive medicine and preventive care. Patch testing and genetic testing are used for identifying the genotype, but patch testing has low accuracy and genetic testing is expensive, time-consuming and having ethical questions. Then we developed an analyzer which can measure breath acetaldehyde and ethanol with high stability, non-invasiveness, and rapidity by applying semiconductor sensor gas chromatograph. Using this analyzer, we developed a method of esophageal cancer risk assessment with high accuracy. The method achieved a sensitivity of 100% and specificity of 92.0% for identifying carriers of inactive ALDH₂ genotypes.

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33.

We have investigated the chemical state of the PdO in catalyst layer on MEMS-gas sensor by the florescence X-ray absorption fine structure analysis of μm order. We found that the PdO in gas sensor was reduced to Pd metal as the gas selectivity decreased. Based on this result we have modified the form of catalyst layer and achieved a long life time of gas selectivity.

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34.

We have developed the MEMS methane gas sensor which has high sensitivity and selectivity with low power consumption. Recently we tried to expand the application for another gas sensing based on the MEMS processing technique in methane gas sensor. It was found that liquefied petroleum (LP) gas, hydrogen or volatile organic compounds (VOCs) can be detected with lower power consumption than that of methane gas sensor by optimizing the heater temperature and driving condition. Moreover, acetone and ethanol can be detected even in a low concentration less than 1ppm.

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35.

In an action for the realization of the hydrogen society of these days, it is important issue using hydrogen more safely. Especially, a sensor detecting a hydrogen leak quickly and precisely is necessary. The contact combustion-type gas sensor is generally used from the viewpoint of linearity with respect to concentration and superior performance to ambient temperature and humidity. However, the sensor needed the response time to hydrogen from several seconds to several ten seconds for this reason, the significant downsizing of the sensor element was necessary for the high-speed sensor response. Therefore, we developed the hydrogen sensor using the MEMS technology in this study. As a result, the response of the micro-gas sensor could be reduced to 40 msec by micro-miniaturization of the sensor element. In additionally, the durability of the sensor was maintained at the same level as that of the conventional-type sensor by attaching a filter to the micro-gas-sensor in atmospheric conditions with poisons substances such as silicon compounds. The hydrogen selectivity of the sensor was controlled by driving at relative low temperature of 300℃ and attaching filter.

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36.

Sensing properties to volatile organic compounds (VOCs) of adsorption/combustion-type micro gas sensors have been examined at an operation with a mode of pulse-driven heating. Among all the sensing materials tested，mesoporous (mp-)Al₂O₃ co-loaded with Pt (1.0 wt%) and CeO₂ (10 wt%) showed the largest dynamic response to 1000 ppm ethanol，while the co-loading with Pt (1.0 wt%) and Bi₂O₃ (10 wt%) to mp-Al₂O₃ largely enhanced the dynamic response to 1000 ppm toluene. The derivative analysis of the dynamic responses indicated that the co-loading with Pt and a suitable metal oxide was effective in controlling the catalytic combustion properties of VOCs as well as the VOC-sensing properties.

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37.

The oxidation of HPO₄^2- on RuO₂-Ta₂O₅ catalytic coatings prepared by thermal decomposition was examined to develop a novel detecting electrode of an electrochemical phosphate ion sensor. Thermal decomposition of a precursor solution containing Ru(III) and Ta(V) was carried out at various metal compositions and temperatures to prepare the detecting electrode. Cyclic voltammetry and chronoamperometry were performed with the obtained electrodes to examine the oxidation behaviors and the concentration dependence of the diffusion-limited current of HPO₄^2-. The oxidation started at ca. 0.8 V vs. Ag/AgCl and the current density was linear to the concentration of HPO₄^2-, in which the amorphous RuO₂-Ta₂O₅ catalyst prepared at 260 oC showed a higher sensitivity than the crystalline one obtained at 500 oC. The sensitivity to HPO₄^2- also depended on the metal composition, and the amorphous catalyst at 50 mol% Ru presented a maximum sensitivity. It was further revealed that the sensitivity of the amorphous catalyst was unchanged in a wide range of HPO₄^2- concentration from 10^-3 mmol/L to 10 mmol/L.

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38.

The deterioration of machine lubricants and engine oils can be commonly estimated through total acid number (TAN), which is the acidity measured by a general titration using KOH(aq.). However, its operation is quite complicated and thus online monitoring the TAN is quite difficult. Therefore, development of solid-state sensors using ion-sensitive field-effect transistor (IS-FET) has been attempted in this study. Both the IS-FET and a reference Ag/AgCl electrode, which were set at the tip surface of general pH sensors, were coated with a cation-conducting polymer film. The sensors obtained were capable of monitoring the acidity of both as-received and heat-treated oils, and the pH values, which were directly measured by the sensors, were relatively correlated with the derived pH values, which were calculated from TAN measured by the general titration method.

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39.

Our group has developed all-solid-state Na ion-selective electrodes with electroactive Na insertion materials as internal mediating layer sandwiched with electrode substrate and ion selective membrane (ISM). In our previous work, various Na insertion materials, which are known as candidate materials for positive electrode of Na ion batteries, were employed as the mediation layer. The double-layer electrodes of Pt/(insertion material)/ISM showed much better potential stability than that of the Pt/ISM electrode (i.e., direct-contact electrode; DCE). Among them, Pt/Na_0.33MnO₂/ISM demonstrated the best Na ion-sensing performance, such as sensitivity, response speed, and potential stability. In this study, effects of the membrane thickness and loading of insertion material were examined to improve the electrochemical performances of the Pt/Na_0.33MnO₂/ISM. Electrode impedance was effectively reduced by optimizing the loading of the insertion material and preparing thinner ion selective membrane, leading to superior electrode performance. Detailed mechanism of the effects will be further discussed.

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40.

We herein report on the development of a phosphate sensor based on an extended-gate type organic field-effect transistor (OFET). The fabricated OFET possesses a detection part functionalized by a Zn(II)-dipicolylamine derivative, which shows a cross-reactive response to phosphate anions. In addition, we have succeeded in detecting a phosphoprotein (=α-casein) using the fabricated OFET sensor. These results suggest that the ultra-low cost and simultaneous detection of organic and inorganic phosphates and phosphoproteins by OFET sensors is potentially achieved in the near future.

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