Sensors based on ion-selective field-effect transistors

2 Sensors based on ion-selective field-effect transistors 

Ever since an ISFET that was chemically modified by a valinomycin-containing PVC membrane was reported [141], there has been general consensus on the advantages of this type of microsensor over conventional ISEs. Some serious problems have also been acknowledged, though e.g. the low mechanical stability of the membranes, the interference of COj in the potentiometric response, the lack of a stable micro-reference electrode and the relatively high drift rate of ISFETs). Attachment of the membrane can 

Cobben et al. [151] designed and tested a wall-jet and a flow-through cell of this type. The wall-jet cell (Fig. 4.19.A) consisted of two parts, A and B. Part A was a Perspex block of 24 x 24 x 20 mm (1) furnished with two resilient hooks (3) for electrical contact. The hooks were pressed on the surface of the contact pads of the CHEMFET (4), the back of which lay on the Perspex surface. In this way, the sensor gate was positioned in the centre of the Perspex block, which was marked by an engraved cross. Part B was 

The flow-through cell developed by Cobben et al. (Fig. 4.19.B) also consisted of two Perspex blocks, A and B. Part A was identical with that used in the previous wall-jet cell, whereas part B (2) was a knotted block (24 X 24 X 15 mm ) into which two holes were drilled towards the centre 

Alegret et al. devised a pH ISFET based on a flow-through cell designed by themselves and an FI manifold including a gas-diffusion module for the on-line separation of gaseous analytes with acid-base properties. In this way, they obtained a linear determination range of 1 x 10 -1 x 10 M for ammonia and 7 x 10 -4 x 10 M for sulphur dioxide, with an RSD of 1% and 0.5%, respectively [153]. 

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