Masao Gotoh

A new BOD estimation method employing a double-mediator system by ferricyanide and menadione using the eukaryote Saccharomyces cerevisiae

A new biochemical oxygen demand (BOD) sensing method employing a double-mediator (DM) system coupled with ferricyanide and a lipophilic mediator, menadione and the eukaryote Saccharomyces cerevisiae has been developed. In this study, a stirred micro-batch-type microbial sensor with a 560muL volume and a two-electrode system was used. The chronamperometric response of this sensor had a linear response between 1muM and 10mM hexacyanoferrate(II) (r(2)=0.9995, 14 points, n=3, average of relative standard deviation and R.S.D.(av)=1.3%). Next, the optimum conditions for BOD estimation by the DM system (BOD(DM)) were investigated and the findings revealed that the concentration of ethanol, used to dissolve menadione, influenced the sensor response and a relationship between the sensor output and glucose glutamic acid concentration was obtained over a range of 6.6-220mgO(2)L(-1) (five points, n=3, R.S.D.(av) 6.6%) when using a reaction mixture incubated for 15min. Subsequently, the characterization of this sensor was studied. The sensor responses to 14 pure organic substances were compared with the conventional BOD(5) method and other biosensor methods. Similar results with the BOD biosensor system using Trichosporon cutaneum were obtained. In addition, the influence of chloride ion, artificial seawater and heavy metal ions on the sensor response was investigated. A slight influence of 20.0gL(-1) chloride ion and artificial seawater (18.4gL(-1) Cl(-)) was observed. Thus, the possibility of BOD determination for seawater was suggested in this study. In addition, no influence of the heavy metal ions (1.0mgL(-1) Fe(3+), Cu(2+), Mn(2+), Cr(3+) and Zn(2+)) was observed. Real sample measurements using both river water and seawater were performed and compared with those obtained from the BOD(5) method. Finally, stable responses were obtained for 14 days when the yeast suspension was stored at 4 degrees C (response reduction, 93%; R.S.D. for 6 testing days, 9.1%).

The advantage of using carbon nanotubes compared with edge plane pyrolytic graphite as an electrode material for oxidase-based biosensors.

Carbon nanotubes (CNTs) are promising materials for use in amperometric biosensors. The defect sites at their ends, and on their sidewalls, are considered to be edge plane-like defects and show high electrocatalytic activity toward several biological molecules. However, electrocatalytic activity toward H(2)O(2) has not been compared among bamboo-structured CNTs (BCNTs), which have many defect sites; hollow-structured CNTs (HCNTs), which have few defect sites; edge plane pyrolytic graphite (EPG); and traditional glassy carbon (GC). The advantages of using CNTs in electrodes for biosensors are still equivocal. To confirm the utility of CNTs, we analyzed the electrochemical performance of these four carbon electrodes. The slope of the calibration curve for H(2)O(2) at potentials of both +0.6 V and -0.1 V obtained with a BCNT paste electrode (BCNTPE) was more than 10 times greater than the slopes obtained with an HCNT paste electrode and a GC electrode, reflecting the BCNTs larger number of defect sites. Although the slope with the EPG electrode (EPGE) was about 40 times greater than that with BCNTPE at +0.6 V, the slopes with these two carbon electrodes were nearly equivalent at -0.1 V. EPGE demonstrated excessive electrochemical activity, detecting currents on the basis of consumption of oxygen and oxidation of ascorbic acid, even at -0.1 V. In contrast, BCNTPE could dominantly detect a cathodic current for H(2)O(2) at -0.1 V, even when interfering molecules were added. BCNTPE possesses appropriate electrochemical activity and is an effective electrode materials for developing interference-free oxidase-based biosensors operated by the application of an appropriate potential.

FET-Biosensor Using Polyvinylbutyral membrane.

The present review describes the FET-biosensor using polyvinylbutyral (PVB) membrane. The PVB membrane was applied to the surface of the silicon nitride which is the gate insulator of the IS-FET (Ion Sensitive Field Effect Transistor). The membrane exhibited good adhesive properties and was used for biomolecules immobilization, such as urease. H+-ATPase, etc.. The water content of the membrane was 27.6% with a thickness of 23, am. The surface structure of the membrane was observed by scanning electron microscopy, which revealed a regular porous microfilter arrangement with a mean pore diameter of 0.25 μm. Immobilized urease activity in this membrane was approximately 20% higher than when a urease-triacetylcellulose membrane was used. Using this polyvinylbutyral membrane, urea sensor, ATP sensor, acetylcholine sensor and HSA sensor were constructed. The new type device of ISFET was also constructed from amorphous silicon. From this device and PVB membrane, glucose sensor, hypoxanthine sensor and inosine sensor were constructed.