Sensors Based on Other Electrochemical Methods

Even with the latest low-noise amplifiers, a distortion-free function of pi-coampere amplifiers is only possible if the complete set-up is enclosed in a Faraday cage (made of metal sheets or grids) which must be grounded. 

Impedance measurement can be considered a third way to evaluate electrochemical sensors besides potentiometry and amperometry. Electrochemical impedance studies in a narrower sense deal with phenomena at the electrode surface. The overall impedance of a chemosensor also includes effects of charge carrier properties far from the electrode. This was visualized by equivalence circuits presented in Chaps. 2 and 5. By individual experimental design, the study can be focused more on processes at the electrode surface or otherwise on ion properties in homogeneous solution. Even the variation of the dielectric constant in a layer will affect the overall impedance. If impedimetry is designed only to acquire data corresponding to ionic properties or value of the dielectric constant, it is not really an electrochemical method, in a strict sense. 

Among the class of impedimetric sensors are real electrochemical sensors where a chemical reaction is the source of information. Of special importance are biosensors with SAMs, which are considered in more detail in the following chapter (Knichel et al. 1995, Rickert et al. 1996). 

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