Sensors chemically modified field effect

In this chapter our work is described that deals with the development of chemically modified Field Effect Transistors (CHEMFETs) that are able to transduce chemical information from an aqueous solution directly into electronic signals. The emphasis of this part of our work will be on the materials that are required for the attachment of synthetic receptor molecules to the gate oxide surface of the Field Effect Transistor. In addition the integration of all individual components into one defined chemical system will be described. Finally, several examples of cation selective sensors that have resulted from our work will be presented. 

Due to their small dimensions, chemically modified field effect transistors are particularly useful for application in flow sensor systems. A double sensor flowthrough cell has been developed for detection of heavy metal ions in aqueous solutions (Figure 3). The cell contains two CHEMFETs of which one is selective for the supporting electrolyte ion (in this case a 0.1 M potassium ion solution) and the other is selective for the heavy metal ion to be detected (Cd , Pb " ). 

Z Brzozka, B Lammennk, D N Remhoudt, E Ghidim, and R Ungaro, Transduction of selective recogmtion by preorgamzed lonophores, K+ selectivity of the different l,3-diethoxycalix[4]arene crown ether conformers, J Chem Soc Perkin Trans 2 (1993) 1037-1040 J A J Brumnk, J R Haak, J G Bomer, D N Remhoudt, M A McKervey, and S J Hams, Chemically modified field-effect transistors, a sodium ion selective sensor based on calix[4]arene receptor molecules, Chm Acta, 254 (1991) 75-80... 

In recent years further concepts have been developed for the construction of polymer-based diodes, requiring either two conjugated polymers (PA and poly(A-methyl-pyrrole) 2 > or poly(A-methylpyrrole in a p-type silicon wafer solid-state field-effect transistor By modifying the transistor switching, these electronic devices can also be employed as pH-sensitive chemical sensors or as hydrogen or oxygen sensors 221) in aqueous solutions. Recently a PPy alcohol sensor has also been reported 222). 

A new type of (bio)chemical sensor, the redox-sensitive field-effect transistor is described It consists of a conventional ISFET with a noble metal added on top of the gate insulator The gate electrode is modified with a redox polymer containing osmium complexes The potentiostatic multi-puls method is introduced which allows the adjustment of the redox potential of the gate to a desired value in a stepwise way It is shown that the open circuit potential after switching off the potentiostat is a good measurement of the presence of the redox active species NADH... 

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