Biomedical subjects

Hirokazu Okuma

Publications and source records attributed to Hirokazu Okuma.

3 recordsLinked to original sources

PubMed2004

Construction of a glucose sensor based on a screen-printed electrode and a novel mediator pyocyanin from Pseudomonas aeruginosa.

Pyocyanin is the blue phenazine pigment produced by Pseudomonas aeruginosa. Pyocyanin production using immobilized cells was investigated. The maximum production of pyocyanin was obtained using cells immobilized in kappa-carrageenan. Moreover, 0.01% PO4(3-), 0.2% Mg(2+), 0.001% Fe(2+), 1% glycerine, 0.8% leucine and 0.8% dl-alanine were also essential for pyocyanin production. Pyocyanin was purified by chloroform extraction and silica gel column chromatography. An amperometric biosensor system using a screen-printed electrode and pyocyanin as mediator were also developed for a more accurate determination of glucose concentration. Pyocyanin, which exists in the oxidated form, was reduced by the reaction between glucose oxidase and glucose. The reduced form was then converted back to the oxidized form by an oxidative reaction on the electrode. There was a linear relation ship between sensor output currents and glucose concentrations ranging from 1 to 20mM under the following conditions: -200 mV of the applied potential, pH 5.0, and 10 U of the immobilized enzyme. The coefficient of variation was below 3% (n = 5) for the glucose sensor.

Biosensing Techniques↗

PubMed2004

Amperometric determination of laminarin using immobilized beta-1,3-glucanase.

A novel sensor system equipped with a reactor packed with beads containing immobilized beta-1,3-glucanase and glucose oxidase was developed for the amperometric determination of laminarin concentration. The proposed sensor system consisted of a reactor, an oxygen electrode, a flow cell, a pump, a buffer tank, and a recorder. The measurement was performed with a flow injection system. The optimum conditions for the sensor system were as follows: transfer solution, pH 7.0; 0.1 M phosphate buffer solution; flow rate, 0.15 ml/min; and sample volume, 50 microl. The response was correlated to the laminarin concentration. The calibration curve was obtained between 50 and 0.5 mg/ml laminarin (R2 = 0.994). The detection limit was 50 microg/ml laminarin (the ratio of signal/noise = 3). The relative standard deviations were 2.0% (n = 15) and 2.5% (n = 15) for 0.4 and 1.0 mg/ml laminarin solutions, respectively. One assay was completed within 5 min. Results suggest that the sensor can be used not only for the analysis of seaweed and health-enhancing foods but also for monitoring the initial pollution of the marine environment.

Biosensing Techniques↗

PubMed2002

Flow system for fish freshness determination based on double multi-enzyme reactor electrodes.

A double reactor system for the determination of fish and shellfish freshness using the freshness indicator, K-value (K=[(HxR+Hx)/(ATP+ADP+AMP+IMP+HxR+Hx)]x100), was developed, where ATP, ADP, AMP, IMP, HxR and Hx are adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, inosine monophosphate, inosine and hypoxanthine, respectively. The system consisted of a pair of enzyme reactors with an oxygen electrode positioned close to the respective reactor. The enzyme reactor (I) was packed with nucleoside phosphorylase and xanthine oxidase immobilized simultaneously on chitosan beads (immobilized enzyme A). Similarly, the enzyme reactor (II) was packed with immobilized enzyme A and immobilized enzyme B (co-immobilized alkaline phosphatase and adenosine deaminase). Moreover, this reactor consisted of two layers, the enzyme A and enzyme B (1:1). A good correlation was obtained between K values, which were determination by the proposed system and by the HPLC method. One assay could be completed within 5 min. The signal for the determination of K value of fish and shellfish was reproducible within 2.3%. The long-term stability of the enzyme reactors was evaluated at 30 degrees C for 28 days.

Adenosine Deaminase↗