Keishiro Tsuda

An enzyme electrode forl-lactate with a chemically-amplified response

Abstract An enzyme electrode with a chemically-amplified response for l -lactate is constructed from an oxygen electrode and a layer containing immobilized lactate oxidase, to oxidize l -lactate, and lactate dehydrogenase, to regenerate the l -lactate. Regeneration enables oxygen to be consumed beyond the stoichiometric limitation, which results in an electrode response amplified 2–250 times according to the variation in the layer properties such as the Vmax and Km values of the immobilized enzymes and the thickness of the layer. The detection limit is as low as 5 × 10−9 M. An equation is derived to relate the rate of oxygen consumption in the layer to the experimental parameters; the equation successfully explains the experimental results.

Photoelectric Effects in Organic Diodes

Photovoltaic behavior of the merocyanine dye family with a rhodanine ring has been systematically studied by employing eight different derivatives in the diode structure Al/evaporated dye/Ag. Each dye film behaves like a p-type semiconductor with a rectifying barrier at Al interface and an Ohmic contact at Ag electrode. The open circuit photovoltage as high as Voc1.5 V was observed for one of the derivatives, while the fill factor remained f.f.0.25 in all cases. The chemical stability of the dye molecules during and after evaporation is also discussed on the basis of the results obtained by the thin-layer chromatography.

The Dependence on Temperature and Hydration of Piezoelectric, Dielectric and Elastic Constants of Bone

The piezoelectric, dielectric and elastic constants of bone are determined at 10 Hz from -150 to 150°C. The piezoelectric constant of dry bone hardly depends on temperature. The piezoelectric constant of 7.4% hydrated bone is larger than that of dry bone at temperatures below 0°C, but smaller at temperatures above 0°C. The former is attributed to the increase of crystallinity of collagen fibrils with hydration and the latter to the increase of ionic conductivity associated with the mobility of adsorbed water. Similarly, the elastic constant of hydrated bone is larger than that of dry bone below 0°C, but smaller above 0°C. Using a model which assumes a parallel combination of collagen fibers and hydroxyapatite crystals, the piezoelectric constant of bone is estimated which is in agreement with the observed value.

Conducting polymer film electrodes with immobilized catalytic sites

Small particles (e.g.platinum black) or neutral molecules [e.g.cobalt(II)meso-tetraphenylporphine] have been immobilized as catalytic sites in a conducting polymer film electrode consisting of polypyrrole-poly(vinyl chloride) alloy.

Effective utilization of dialysate by a successive batch dialysis method

透析液の有効利用を図るために, 小容量の透析液バッチ槽を用い, これを一定時間毎に切り替える連続的バッチ透析法を考案した. 本方法による透析液節減効果について, one pool modelに基づくシミュレーション解析を行ったところ, 除去対象物質について臨床データ (体液量, 体内産生速度, 初期濃度), 透析条件 (全透析時間, 透析器ダイアリザンス) および除去必要量を設定することにより, 透析液必要量を最小にする最適バッチ透析条件 (バッチ槽体積, 切り替え時間およびこれに対応する切り替え回数) を求めることができた. 尿素を対象物質とすると, バッチ槽体積の増加とともに最適切り替え時間は増加したが, 透析液の使用量は, 除去必要量が少ない (25g以下) 場合に若干の低下傾向がみられるのを除き, 除去必要量にかかわらずほぼ一定であった. この成績から, 本法では通常のシングル・パス透析法と比較した場合透析液使用量が約50%低減し, 透析液利用効率の向上が示された. これらの検討結果に基づいて, 連続的バッチ透析装置の設計, 試作を行い, in vitro実験を行ったところ, シミュレーション解析の予測と良い対応を示した. 以上の成績より連続的バッチ透析法は, 血液透析における透析液必要量を節減し, そのコスト・パーフォーマンスの向上に有用であると考えられた.