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CHAPTER 10 S URFACE A COUSTIC W AVE S ENSORS FOR C HEMICAL A PPLICATIONS Adeel Afzal Franz L. Dickert 1. INTRODUCTION Nowadays analytical chemistry benefits from a large arsenal of a variety of methods and state-of-the- art instruments for precise determination of trace quantities of various substances and for analysis of complex mixtures. Simultaneously, these technologies also have some disadvantages, e.g., they are ex- pensive, require trained personnel, and in numerous cases they are complicated and laborious. However, the development of chemical sensors for remote, selective, and fully automated detection of various analytes in liquid and gaseous states has recently emerged as a valuable initiative. These robust, small, easy-to-use, and economical devices are usually capable of continuously detecting chemical substances and analyzing complicated mixtures. A chemical sensor is basically a transducer system that transmits chemical information in the form of an analytically useful signal, i.e., current, voltage, or frequency. The frequency-output sensors utilize acoustic wave resonators such as quartz crystal microbalance (QCM) and surface acoustic wave (SAW) resonators as transducers. This chapter emphasizes the principal sen- sors based on SAW resonators and reviews state-of-the-art SAW sensor technology, sensor characteristics and response, and a range of applications. Subsequent pages also include detailed review of the materials used as coatings for SAW devices, their interaction with the analyte of interest, and sensor effects. At the end, a comparison of QCM and SAW devices is given along with the market and future prospects for SAW sensors. 447