Yusuke Okawa

Tethered mediator biosensor. Mediated electron transfer between redox enzyme and electrode via ferrocene anchored to electrode surface with long poly(oxyethylene) chain

In order to build an electronic interface between a redox enzyme and an electrode, we have designed a new mediator system, where the mediator molecule is immobilized onto an electrode surface via a long flexible chain-“tethered” mediator. As a prototype tethered mediator system, a ferrocene derivative with a long poly(oxyethylene) chain was immobilized onto an SnO2 electrode and electron mediation function to horseradish peroxidase (HRP) was examined. In the cases of both soluble and co-immobilized HRP, we observed a catalytic current for hydrogen peroxide reduction. The kinetic analysis exhibited that the tethered ferrocene effectively mediates electron between the enzyme and the electrode.

Model analysis of enzyme monolayer- and bilayer-modified electrodes: the transient response.

The transient responses of enzyme monolayer- and bilayer-modified electrodes were theoretically analyzed. The response was numerically simulated with parameters used in the foregoing paper. The transient process consists of three elementary steps: enzymatic reaction step, substrate and mediator consumption step, and charge-carrying mediator accumulation step. Contributions of the parameters to these elementary steps and the overall response were examined. Experimental observations are successfully interpreted in terms of the theoretical results.

Bifunctional Langmuir-Blodgett film for enzyme immobilization and amperometric biosensor sensitization

Abstract A Langmuir-Blodgett (LB) film consisting of octadecylamine as the binding site for the enzyme molecule, an amphiphilic ferrocene derivative as the electron mediator, and octadecanol as the matrix for these molecules was deposited on a hydrophobized tin oxide (SnO 2 ) electrode. Glucose oxidase (GOx) was then covalently immobilized on the film via glutaraldehyde, and the GOx electrode thus obtained worked as an amperometric glucose sensor based on the oxidation of hydrogen peroxide liberated by the enzymatic reaction. The sensitivity of this sensor was about twice as high as that of a GOx electrode prepared with the same LB film as above but without the ferrocene. The sensitizing effect of ferrocene was attributed to its capability of electron mediation between hydrogen peroxide and the SnO 2 electrode.

Rheological Study on Gelatin Gelation

AbstractChanges in the rheological properties of a gelatin solution during gelation were studied. Samples with various concentrations (0.1-6.0 wt%) were cooled from 45°C to 10 °C at a constant cooling rate and then kept at 10 °c. When the sample was cooled to a certain temperature, the viscosity started to increase. A steep rise in rigidity was observed after the viseosity increase. The vatlie of tanδ of each sampIe first increased and then decreased and converged to a characteristic vallie. We can understand this behaviour well in the framrwork of percolation transition theory. Concentration dependence of the rheological behaviour in the gelation process suggests that the gel structure of 1.5wt% samples are different. In the higher concentration region, almost all the crosslinking points take part in the gel network formation, and thus the gels all feature an essentially similar structure. In the lower concentration region, some of the crosslinking points become dangling b...

Direct and simultaneous determination of uric acid and glucose in serum with electrochemical filter/biosensor flow-injection analysis system☆

Abstract A flow-through electrolysis cell, named an electrochemical filter (ECF), with a three-electrode configuration was developed for the elimination and determination of electrochemically active components in biofluids, which give generally a nonspecific response to electrochemical biosensors. The use of a reference electrode ensured the precise control of the working electrode potential of the ECF and thus the quantitative current efficiency of the electrolysis. A flow-injection analysis setup was constructed by connecting two ECFs and a flow-through amperometric biosensor for glucose in series for the direct and simultaneous determination of glucose and uric acid in serum. The first ECF coulometrically determined uric acid, and the second one eliminated interferents with the biosensor: the sample was thus treated on-the-fly and then delivered to the biosensor, so that it determined glucose amperometrically without interference. The concentrations of glucose and uric acid measured in human control sera agreed well with the values determined with conventional methods. The system exhibited the wide dynamic range in the high glucose concentration region, thus can be applied to the analysis of serum of hyperglycaemic patients.

The Effect of the Thermal History on the Gelation of Gelatin solution

AbstractWe have studied the effect of the thermal history on the gelation of an aqueous solution of gelatin by differential scanning calorimetry (DSC).DSC has shown that the heat affusion and the melting point of gelatin gels are related to the maturing temperature.An experimental study of the structure of gelatin gels by wide angle X-ray diffraction (WAXD) is described. Some workers have reported that the presence of a crystalline structure was not seen in the WAXD pattern of gelatin gels containing a high amount of water, therefore, we made gelatin gels at several fixed temperatures and dried them at the same temperatures. The gelatin films made under such controlled temperature conditions were used as the samples for WAXD determination.The gelatin film gelled and dried at a higher temperature had a lower content of triple-helices but denser bundles of the triple helices in the junction zone than the gelatin film made at a lower temperature.The heat offusion and the melting point of gelatin gels obtaine...

On the rates of gelation and the setting points of gelatin solutions

AbstractSetting temperature and setting time were obtained readily with good reproducibility. Setting speed was defined from these two values.The relationship between the concentration (C), the cooling temperature <T) and the setting time (t) of the gelatin solution was studied using one IAG- gelatin (M-8929). The relation of these three factors could be expressed empirically as: Int=a+b(C/T)from which can be found the characteristic point of the gelation. It seems that this value is related to the factors controlling the gelation.We could not find the characteristic point of the gelation for gelatin containing little high molecular weight components, resulting from ultrasonic wave irradiation.

Effect of the filtration of PbI2 solution for zinc oxide nanowire based perovskite solar cells

Zinc oxide (ZnO) nanowires (NWs) are grown on fluorine-doped tin oxide (FTO) glass substrates via a simple reactive evaporation method without the presence of any catalysts or additives. The ZnO NWs show high crystallinity and preferential elongation along the c-axis of the hexagonal wurtzite crystal structure. The highly crystalline NWs as electron transporting layer have been used to fabricate the CH3NH3PbI3 perovskite solar cells and their photovoltaic performance were investigated. In this report, we studied the effect of filtration of PbI2-solution on surface morphology of CH3NH3PbI3 layer. Spin-coating of the filtered PbI2-solution leads to a better crystallization and relatively homogenous coverage of the CH3NH3PbI3 film, resulting in an enhancement of the solar cell efficiency compared to the cell fabricated using non-filtrated PbI2-solution. By synthesizing the CH3NH3PbI3 film using filtrated PbI2-solution, we achieved the best power conversion efficiency of 4.8% with a current density of 7.6 mA cm−2, the open circuit voltage of 0.79 V and fill factor of 0.63.

Hydrothermal synthesis of one-dimensional yttrium hydroxide particles by a two-step alkali-addition method

One-dimensional yttrium hydroxide particles of hexagonal crystal structure were selectively synthesized through a hydrothermal reaction of yttrium chloride solution that was alkalized by two-step addition of sodium hydroxide solution. Keeping the YCl3 solution at pH ∼ 6.8 for a few minutes before raising the pH to the sufficient level (pH ∼ 13) was concluded to be the practical requirement for the one-dimensional Y(OH)3 particle formation. This requirement was successfully achieved by the two-step addition procedure that was applicable to adjust the pH values independently. The size distribution of one-dimensional particles was changed depending on the interval time between alkali-additions and on the pH of the hydrothermal reaction. The formation mechanism of the one-dimensional particles was also discussed.

Development of a Movable Inspection Sensor for a Pipe Using an Electromagnetic Acoustic Transducer of the Magnetostriction Effect Type

Electromagnetic acoustic transducers (EMATs) using the magnetostriction effect have many advantages for nondestructive inspections. For example, this type of EMAT easily generates an ultrasonic wave in magnetic material samples without any contact, which does not require a coupling medium, and thus is movable and can easily be installed. The objective of this study is to develop a nondestructive inspection technique using a pipe wave, a type of ultrasonic wave that can travel a long distance along a pipe, which can be used as a nondestructive inspection method with an EMAT. The pipe wave must be selected to have an optimum mode to diagnose the shape or depth of defects. We developed EMATs for a torsional mode (T-mode) pipe wave and a longitudinal mode (L-mode) pipe wave. We then machined several defects in the test pipes and attempted to inspect them. The results show that the trial EMATs have the potential to distinguish the type, sizes and depth of defects.