電界効果トランジスタ形ケミカルセンサとその応用

抄録

The Ion Sensitive Field-Effect Transistor (ISFET) is a new device for sensing cation activity in the electrolyte. This device is similar to the conventional MOSFET except that the gate insulator is exposed to solution. The gate insulator plays the role of an ion selective electrode and its potential can be detected by its FET action. ISFET's have potential advan-tages over conventional ion selective electrode in their rapid response, small size and low output impedance, and are extremely attractive for biomedical applications.
The chemical responses of ISFET's depend on its surface materials. A nearly ideal pH response, excellent stability and selectivity to other cations are obtained using Al₂0₃ or Ta₂O₅. On the other hand, SiO₂ shows a poor response and it is proved that the oxygen content in Si₃N₄ surface degrades its properties as a pH sensor.
Sodium-alumino-silicate glass (NAS glass), which is generally known as a material for pNa, pK selective glass electrodes, is utilized as a surface material for the pNa and pK ISFET. The selectivities of these devices are comparable to that of the conventional pNa pK glass electrodes.
Some applications of ISFET are also described, that is, micro ion sensor, multi-ion sensor (pH and pNa), combined pH sensor, and pCO₂ sensor.