Hiroyuki Miyagi

Field-effect transistor using a solid electrolyte as a new oxygen sensor

A field‐effect transistor (FET) using a solid electrolyte is proposed in the present study as a new oxygen sensor. The sensor is fabricated by depositing a thin layer of yttria‐stabilized zirconia (YSZ) on a gate insulator of an insulated gate field‐effect transistor (IGFET). As an IGFET has an ability to transform impedance, the potential change produced at the interface between the YSZ layer and a platinum gate electrode can be detected stably, even if the impedance of the YSZ is very high. The response of the fabricated sensor showed good reproducibility at 20 °C. A linear relationship between output voltage and logarithmic partial pressure of oxygen was obtained in the range from 0.01 to 1 atm. Sensitivity of the sensor was found to depend on the thickness of the Pt‐gate electrode and sputtering conditions of the YSZ layer. Although selectivity to hydrogen and carbon monoxide was not good at room temperature, it could be improved by increasing the operating temperature to 100 °C. The developed sensor ...

Long-life multiple-ISFETS with polymeric gates

Abstract Long-life, integrated multiple-ISFETs with CMOS interface circuits have been developed. The interface circuits are designed for impedance conversion and rapid multiplexing of the signal from each ISFET. Three kinds of ion-selective membranes for sodium, potassium and chloride are formed on the gates and separated by a patterned thick polyimide layer. The poor adhesion of the polymeric membrane to the ISFET gate is improved by selecting the proper plasticizer for use in the membrane. As a result, a chemical response for sodium, potassium and chloride can be obtained for more than two months.

An integrated chemical sensor with multiple ion and gas sensors

Abstract An integrated chemical sensor with multiple ion and gas sensors, composed of four ISFETs (pH, Na + , K + and Cl − ) and two gas sensors ( P O 2 and P CO 2 ) on a 4 mm × 4 mm chip, is realized using semiconductor processing. The ISFETs are based on an Si 3 N 4 -gate ISFET, and use polymeric membrane except for the pH ISFET. The P O 2 sensor is a miniaturized Clark-type sensor, consisting of a Pt cathode and Ag/AgCl anode patterned by the lift-off process. The P CO 2 sensor is a miniaturized Severinghaus-type sensor using a pH ISFET. All of the ISFETs show sensitivities over 50 mV/decade, and a linear range between 1 × 10 −4 and 5 × 10 −1 mol/l. The sensitivities of the P O 2 and P CO 2 sensors are 0.35 nA/mmHg and 42 mV/decade, respectively, and their response times are 30 s and 1 min, respectively. The integrated chemical sensor with multiple ion and gas sensors could be used for clinical analysis.

Anion-selective electrodes based on long-chain methyltrialkylammonium salts

A new series of methyltrialkylammonium salts with an alkyl chain length (n) longer than the conventional methyltridodecylammonium (MTDDA, n = 12) has been developed, and these materials were examined for use as the ion-sensing component (ligand) in anion-selective electrodes (ISEs). Syntheses of the higher ammoniums with n = 16, 18, and 20 were carried out. In combination with an alcoholic plasticizer, the ammoniums with n = 12, 16, and 18 led to ISEs with fundamental characteristics, such as slope sensitivity, impedance, and time response, that were sufficient for practical applications. Compared with the conventional MTDDA, the ISEs based on the ligands of n = 16 and 18 showed marked improvement in chloride selectivity over both lipophilic and hydrophilic anions, deviating from the Hofmeister regime in some cases. Taking perchlorate as an example, the magnitude of the improvement was a factor of 20 for n = 16 and 15 for n = 18. When the new ISEs were applied to chloride analysis in blood serum, they improved the accuracy by a factor of 2-6. Therefore, the methyltrialkylammonium salts with alkyl chain lengths of 16 and 18 offer definite advantages over the conventional alternative and are strong candidates to become the standard compounds for use in future chloride ISEs.

Determination of urea in whole blood using a urea electrode with an immobilised urease membrane

A urea electrode using an ammonium ion-selective electrode with an immobilised urease membrane is described. The measurement of blood urea was carried out accurately without any pre-treatment of the samples. A conversion equation related to haematocrit was derived, which made it possible to determine plasma urea concentration from whole blood urea concentration. Rapid determinations of plasma urea concentrations were also made possible.

Urea sensor based on an ammonium-ion-sensitive field-effect transistor

Abstract A urea sensor based on an ammonium-ion-sensitive field-effect transistor has been realized in combination with an immobilized urease membrane. The effect of buffer concentrations on the response characteristics of the sensor is investigated. The lower detection limit, as given by the calibration curve, is strongly affected by the concentrations of potassium and sodium ions, while its slope in the appropriate buffer solution is independent of the buffer concentration in a limited urea concentration range. Although the slope in physiological saline solution is only 18 mV/dec, the dynamic range of the sensor covers the physiological range of urea in blood. The small slope and the narrow dynamic range are found to be due to poor selectivity of the ammonium-ion-selective membrane over sodium and potassium ions. It is, therefore, possible to improve the sensor response characteristics by improving the selectivity of the ammonium-ion-selective membrane.

High-sensitivity micro ultraviolet absorption detector for high-performance liquid chromatography

Abstract A UV absorption detector with a 0.6-μl flow cell for high-performance liquid chromatography (HPLC) was developed. In order to improve the signal-to-n

An integrated micro multi-ion sensor using platinum-gate field-effect transistors

An integrated micro multi-ion sensor was designed and fabricated for a high-performance ion sensor applicable to clinical analyses. Platinum gate ISFETs (ion-sensitive field effect transistors), which have a platinum block layer for protection from ion migration and dissolution and are compatible with MOSFETs, are used. The sensor chip consists of, two kinds of ion sensors (K/sup +/ and Na/sup +/ ISFETs) and two CMOS unity-gain buffers. The output voltages are equal to the equivalent gate membrane potentials of the integrated ISFETs and show a wide linear dynamic range. The K/sup +/ and Na/sup +/ ISFETs show good chemical responses, including sensitivities, selectivities, and drifts, which are compatible with those of conventional ion-selective electrodes.<<ETX>>

Platinum-platinum oxide gate ph isfet

Platinum-platinum oxide gate ISFETs (ion sensitive field effect transistors) have been designed and fabricated for a stable pH microsensor. The platinum oxide layer, formed by a new fabrication process using an RF sputtering technique, was identified as PtO2 by X-ray photoelectron spectroscopy. The pH response of the platinum-platinum oxide gate ISFET was linear in the pH range between 1 and 10, and a sensitivity of 40.5±4.0 mV/pH was obtained. The ISFET developed had better stability than a conventional Si3N4 bare gate ISFET.

Analysis of body functions using a clinical liquid chromatograph

A clinical liquid chromatograph, which consists of a completely automated liquid chromatograph combined with a microcomputer for diagnosis, and its application to body function analyses are described. The analytical rate for urinary ultraviolet-absorbing constituents using anion-exchange chromatography was 12 samples per day, and the reproducibilities for retention time and peak area were less than 3% and 4%, respectively. Diagnostic methods for kidney functions using the chromatograms are discussed.