Chemical Microsensors and Microanalysers Essential Components of Microsystems

Abstract

Sensors, which probe the physical and chemical status of their surroundings, together with the microelectronic components that subsequently perform the data evaluation or processing, and the actuators that carry out the decisions thus derived, constitute the three essential parts of a microsensor system. New microsystem technological solutions appear to be the right approach to meet the rapidly increasing demand for process and environmental control and monitoring instrumentation as well as for clinical diagnostics. Fundamental to the wider uptake of such systems is the availability of chemical microsensors or microanalysers which can be incorporated into microsystems and which meet the required specifications as far as selectivity, sensitivity and stability, combined with fast response times and longevity, are concerned. Two lines of development are being discussed. The first is based on the miniaturisation of conventional laboratory analysis equipment, leading to chemical microanalysers exemplified by the near infrared fibre evanescent field absorbance probe and the thermal lens technique. In contrast to these methods, which are mainly based on physical interactions (of photons) with the analyte, the second line, the development of chemical microsensors, depends on chemical interaction of the analyte with a chemically selective layer of the sensor. This chemical interaction is transformed by suitable transducers into an electronic or optical signal. The problems involved in the development of the chemical sensors and their potential applications are demonstrated by the discussion of three microchemical sensor types: the surface acoustic wave sensor, the optochemical sensor (optrode) and the chemically modified field effect transistor.