Yuji Mishima

Utilization of an osmium complex as a sequence recognizing material for DNA-immobilized electrochemical sensor

Abstract A novel immobilized DNA electrode based on a porous carbon electrode was prepared to study interactions between DNA and chemical compounds. The characteristics of this electrode were evaluated by electrochemical methods, and then the interaction between DNA and an osmium complex was studied. On this electrode (electrode surface; 0.66–2.37 cm2), DNA was immobilized at 0.26 × 10−4 − 1.23 × 10−4 mol cm−2. Hybridization of DNA was observed with a relative standard deviation of 11% (n = 4). The tris(bipyridyl)osmium(II/III) ion (osmium complex) was found to interact to major or minor grooves. Using this osmium complex, a DNA sequence could be recognized with more than 12 mer of the same sequence.

Glucose sensor based on titanium dioxide electrode modified with potassium hexacyanoferrate(III)

Abstract A potassium hexacyanoferrate(III) modified titanium dioxide electrode with immobilized glucose oxidase (GOD) was developed for measuring glucose. With this electrode, glucose concentration (1×10 −5 to 1×10 −3 M) could be determined accurately in the presence of ascorbic acid or uric acid. Glucose in human serum was determined after diluting the serum 10-fold with phosphate buffer of pH 5.5. The glucose concentrations of 70.5–72.7 mg dl −1 were determined in good agreement with those usually found in human serum.

Development of a D-amino acids electrochemical sensor based on immobilization of thermostable D-Proline dehydrogenase within agar gel membrane

A novel biosensor for determination of d-amino acids (DAAs) in biological samples by using an electrode based on immobilization of a thermostable d-Proline dehydrogenase (d-Pro DH) within an agar gel membrane was developed. The electrode was simply prepared by spin-coating the agar solution with the d-Pro DH on a glassy carbon (GC) electrode. An electrocatalytic oxidation current of 2,6-dichloroindophenol (DCIP) was observed at -100mV vs. Ag/AgCl with the addition of 5 and 20mmolL(-1)d-proline. The current response and its relative standard deviation were 0.15muA and 7.6% (n=3), respectively, when it was measured in a pH 8.0 phosphate buffer solution containing 10mmolL(-1)d-proline and 0.5mmolL(-1) DCIP at 50 degrees C. The current response of d-proline increased with increase of the temperature of the sample solution up to 70 degrees C. The electrocatalytic response at the d-Pro DH/agar immobilized electrode subsequently maintained for 80 days. Finally, the d-Pro DH/agar immobilized electrode was applied to determination of DAAs in a human urine sample. The determined value of DAAs in the human urine and its R.S.D. were 1.39+/-0.12mmolL(-1) and 8.9% (n=3), respectively.

RECOVERY AND EXTRACTION OF HEAVY METAL IONS USING IONIC LIQUID AS GREEN SOLVENT

Ionic liquids are expected to replace conventional organic solvents in organic synthesis, solvent extraction and electrochemistry due to their unique characters such as low volatility, high stability and so on. In this work, N,N,-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis(trifluoromethansulfonyl)imide was used as an alternative solvent to extract heavy metal ions. As the extracting conditions, the additional effect of 8-hydroxyquinoline (8-HQ) as metal chelating agent into ionic liquids, shaking time and volume ratio were investigated. As extraction efficiency depended on 8-HQ concentration significantly, in order to extract high concentrated metal ions the solubility of 8-HQ into ionic liquid was tested. N,N,-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis(trifluoromethansulfonyl)imide had good solubility of 8-HQ. Consequently, 5 μmol of copper, zinc, cadmium and manganese could be completely recovered with 100 μl of ionic liquid.

Interaction between immobilized DNA and tris(bpy)osmium(II/III) complex

Abstract The interaction between a tris(bipyridyl)osmium (II/III) ion (osmium complex) and immobilized DNA was studied. The amount of immobilized DNA on the prepared carbon paste electrode (surface area; 0.66–2.37×10−2 cm2) was 0.26–2.78×10−4 mol cm−2. Compared with the bare porous electrode (584 mV), the equilibrium potential of osmium complex with the immobilized single strand DNA electrode shifted to the higher side (650 mV). On the other hand, the equilibrium potential of one with the immobilized double strand DNA (dsDNA) electrode shifted to the lower side (542 mV). These results suggest that the osmium complex interacted specifically with dsDNA. The amount of the osmium complex on immobilized dsDNA electrodes was determined and it gave a good linear plot in the concentration range of 0.5 to 4 mM.

Detection of DNA segment utilizing an immobilized DNA electrode and an osmium complex

Abstract The interactions of an osmium complex with immobilized dsDNA and ssDNA electrodes were studied by linear sweep voltammetry. The appearance of an oxidation peak of the complex indicated that the osmium complex specifically interacted with dsDNA. The osmium complex was concluded to interact electrostatically with phosphate groups, and nonelectrostatically with base pairs and/or the sugar backbone. Recognition of DNA sequences by the osmium complex was examined. The immobilized ssDNA electrode was hybridized with probes, and then the charge of DNA hybrids were measured in phosphate buffer (pH 7.0). After interaction of this electrode with the osmium complex, the charge of the complex was measured in phosphate buffer (pH 7.0). Results showed that complementary probes of more than 12 mers were recognized by the osmium complex, and so that the osmium complex binds to major or minor grooves of the DNA helix.

Nonsuppressed Ion Chromatography of the Mixture of Urea and Alkali Metal Ions Utilizing the Enzyme Reaction

Abstract Non-suppressed ion chromatography with an immobilized enzyme reactor was developed for the simultaneous determination of urea and alkali metal ions. The enzyme reactor was prepared by immo...

Electrochemical evaluation of the polymer modified micro-electrode for metal ions

A porous micro-electrode with immobilized poly(methacryroyl alanine) (PMA) was developed for measuring copper(II) ion (Cu2+) and cadmium(II) ion (Cd2+). A porous carbon material was packed into the tip of the platinum micro-electrode with a cavity at the top. The porous micro-electrode was dipped in the coating dimethyl sulfoxide solution with PMA and di-2-ethylhexyl phthalate and dried overnight at room temperature. The immobilized PMA on the porous micro-electrode had predominantly a keto form in the buffer solution. In the enol form a metal complex can be formed under the simultaneous liberation of a proton. Calibration curves for measurements of Cu2+ and Cd2+, the effects of preconcentration condition, scan rate, pH, and temperature, and lifetime of the PMA modified micro-electrode were examined. Under optimal conditions, the responses of sensor were linear in the concentration range 0.0001~1 mmol 1-1 for Cu2+ and 0.01~1 mmol 1-1 for Cd2+. Analytical values determined with the modified electrode were constant for at least 3 month.

Enzyme Biosensor Based on an Electropolymerized Osmium Redox Polymer

Electrochemical polymerizations of metal complex as electron mediator in aqueous solution have been developed. The metal complexes as electron mediator of biosensor for practical application have a rapid electron transfer rate, a chemical stability, and an accessible manipulation. The electro-polymerized redox polymer relatively decreased the enzyme and catalytic activity, although these could be treated in organic solvent. In this work, the water-soluble osmium complex-modified pyrrole derivatives with long, flexible spacer chain were synthesized. The electro-polymerized redox polymer was generally produced by potential sweep copolymerization (-400 mV -/+1200 mV (vs. Ag|AgCl(sat.KCl))) of water-soluble osmium complex-modified pyrrole monomer and glucose oxidase (GOD) on the top of a Pt electrode in aqueous solution. With the electro-polymerized osmium redox polymer modified electrode, calibration graphs for measurements of glucose and the effect of concomitant compounds, dissolved oxygen and the lifetimes of the sensor were electrochemistry examined, respectively. Under optimal conditions, the response of the sensors was in the concentration ranges of 0.6 mM-100 mM for glucose.