Naomi Kojima

A miniature Clark-type oxygen electrode using a polyelectrolyte and its application as a glucose sensor

A miniature Clark-type oxygen electrode was fabricated by anisotropically etching silicon. A two-gold-electrode configuration was used and a double-layered gas-permeable membrane was formed directly on the electrolyte, poly(vinyl-4-ethylpyridinium bromide) in the sensitive area. These materials improved the electrodes stability in long-term storage and sterilization tolerance to a practical level. The 90% response time averaged 80 s and residual current 10%, with a good linear calibration curve. The oxygen electrode was also used to make an integrated sensor for the simultaneous determination of glucose and oxygen. The glucose sensors response time was 50-110 s, with good linearity in glucose concentrations between 56 microM and 1.1 mM at 37 degrees C, pH 7.0.

Miniature Clark-type oxygen electrode with a three-electrode configuration

Abstract A Clark-type oxygen electrode with three electrodes has been fabricated using semiconductor techniques and its characteristics compared with those of double oxygen electrodes with a similar structure. The 90% response time is 40 s, the residual current at zero oxygen concentration is less than 7%, and the linearity is good. The oxygen electrode can be used for 25 h at −0.6 V. These characteristics are affected by electrochemical crosstalk between the electrodes and are improved by varying the electrode configuration.

Development of a miniature clark-type oxygen electrode using semiconductor techniques and its improvement for practical applications

Abstract A disposable minature Clark-type oxygen electrode has been fabricated using semiconductor techniques. The oxygen electrode consists of: (a) anisotropically etched U- or V-grooves on a (100) silicon substrate as the electrolyte container; (b) a calcium alginate gell containing a 0.1 M KCl electrolyte; and (c) a directly formed gas-permeable membrane. A two-electrode configuration is used with a gold cathode and a gold anode. A novel fabrication process has been developed to allow miniaturization and mass production. Several important factors which influence the oxygen electrode characteristics have been examined. A 90% response time of 10 s is attained. A linear relationship is observed for a wide range of oxygen concentrations at 27°C. 34% of the oxygen electrodes work normally after sterlization in an autoclave. The oxygen electrode can be operated continuously for more than 40 h.

Disposable oxygen electrodes fabricated by semiconductor techniques and their application to biosensors

Abstract We fabricated a miniature Clark-type oxygen electrode using semiconductor techniques. The oxygen electrode features V-grooves to contain a 0.1 M KCl electrolyte impregnated in a gel, and a directly formed gas-permeable membrane over the gel. A fast response and a good linearity from zero oxygen concentration to saturation was obtained using the Ag/AgCl anode. The oxygen electrode was used in a disposable miniature CO 2 sensor. Also, an l -lysine sensor was developed that functions by immobilizing l -lysine decarboxylase on the sensitized area of the CO 2 sensor.

Effect of anode materials on the characteristics of the miniature clark-type oxygen electrode

Abstract A miniature Clark-type oxygen electrode was fabricated using semiconductor techniques. A two-electrode configuration was used and the effect of different anode materials on the characteristics of the oxygen electrode was examined. The cathode and anode were formed in anisotropically etched grooves and calcium alginate gel containing 0.1 M KCl electrolyte filled the grooves. A gas-permeable membrane was directly formed over the gel. By using an Ag/AgCl anode instead of a gold electrode, the response time was shortened, the residual current was decreased and the linearity of the calibration graph was improved. Good linear calibration graphs were obtained by using the Ag/AgCl anode. The Ag/AgCl anode oxygen electrode produced a stable current for 5 h at −0.8 V and for 22 h at −0.6 V.

Giant magnetoresistance properties in multilayered Co‐Ag/Cu granular alloys

In this article, we introduce a novel Co‐rich Co‐Ag/Cu granular alloy structure with increased magnetic sensitivity, and report on our study of the relationship of giant magnetoresistance (GMR) and magnetic properties to annealing temperature and Cu thickness in sputtered Co66‐Ag34/Cu multilayered films. We heat treated Co‐Ag/Cu films with Cu spacer thickness ranging from 15 to 50 A up to 500 °C, and found that the MR ratio loosely depends on both the Cu spacer thickness and the annealing temperature, peaking at 7.6% with a 25 A Cu layer and an annealing temperature of 280 °C. Based on the magnetic properties we observed, as well as x‐ray studies, we found that Cu spacers at least 25 A thick are able to separate the Co‐Ag magnetic layers. Our data also indicated that the annealing treatment changed the coupling of magnetic layers from ferromagnetic to antiferromagnetic. The high thermal stability and the high magnetic sensitivity suggest potential use of our novel multilayered structure in applications as...