Chemical imaging: II. Trends in practical multiparameter sensor systems

Abstract

In most applications of chemical sensors today the original output of an individual sensor is monitored as one ‘feature’ (such as a certain current at a fixed potential of an electrochemical cell or a resistance of a metal oxide sensor). However, individual sensors and the determination of individual features show limited performance only for most practical applications. Often, arrays of many sensors and an extension of the feature space are required. In this context, a general trend is to be seen now towards more perfect ‘chemical imaging’: the final goal is a time and spatially resolved electronic recording of many individual chemical species, of toxicity, of odour impression etc. Part I of this paper dealt with the systematics of chemical imaging with sensor systems, i.e. with theoretical concepts to obtain a high-dimensional ‘hyperspace of chemical features’ and to deduce information from this space. This paper describes examples of already realised components of such sensor systems. They are used to increase the number of independent chemical sensor features as a prerequisite for advanced chemical imaging. The evident first strategy to produce independent features by the choice of different sensor-active materials has been treated in many reviews and is therefore not discussed here. The new practical approaches to produce features with corresponding prototype sensors presented in this overview are organised according to the following scheme: similar sensitive layers are investigated as coatings on different transducers, the same sensitive layer is investigated with a single transducer, recording occurs of different physical properties, and the same sensitive layer and transducer and the same physical property is recorded in different modes of sensor operation.