Yasuhisa Shibata

Using acoustic radiation force as a concentration method for erythrocytes

We investigated the potential damage inflicted on erythrocytes by acoustic radiation force when the cells are concentrated by a 500-kHz ultrasonic standing wave at the pressure node. The extent of the damage was estimated from the concentrations of potassium ions, iron complexes, and lactate dehydrogenase released from the cells. After 2 min of ultrasound irradiation at 12.8 mJ/m3, the cells concentrated on the pressure node, with a cell distribution half-width of 138 microns; no significant release of intracellular components was detected, even after 15 min of irradiation. The results indicate that even small ions like potassium are not released as a result of ultrasound irradiation on cell membranes without cavitation, and they demonstrate the potential use of acoustic radiation force for concentrating living cells in biomedical applications.

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.

Long-life planar oxygen sensor

Abstract A planar amperometric oxygen sensor has been developed using a printing method for an Ag anode and a four-layered structure for an electrolyte solution. The sensor consists of four glass substrates stuck together by epoxy resin. A Pt cathode and an Ag anode are deposited on one of these glass substrates by r.f. sputtering and by printing, respectively. An internal electrolyte solution is enclosed in the structure and sealed off by an oxygen-permeable membrane. A linear relationship is obtained between the reduction current and the partial pressure of oxygen in the range 0–600 mmHg. The current at an oxygen pressure of 100 mmHg is stable for more than 2000 h. The amount of Ag anode patterned by the printing method is found to be sufficient for continuous long-term use. Based on methods and structures similar to those described in this paper, it should be possible to fabricate miniaturized oxygen sensors and biosensors.

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>>