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HAMAMATSU CORPORATIONpubs.acs.org/doi/pdf/10.1021/ac00186a728To date, no chemical vapor sensors have been developed that...

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REPORT and Wohltjen's cyclopentadiene sensor (29) and Zellers's styrene and vinyl ace­ tate sensors (5,30), which are of partic­ ular interest because reagent is sus­ pended in a semiselective polymer film. Corrections are made for nonspecific sorption into the film by coating one side of a dual device with the reagentpolymer mixture and the reference side with the polymer alone. An additional advantage of these sensors is that re­ agents can be regenerated, whereas the cyclopentadiene-poly(ethylene maleate) system is generally irreversible. This approach has the advantage of in­ creased chemical specificity and can be useful when a well-known hazard exists or when the ambient environment is under partial control, such as in indus­ trial hygiene applications or in the monitoring of industrial processes. Future directions To date, no chemical vapor sensors have been developed that take advan­ tage of the sensitivity of the SAW de­ vice to changes in the shear elastic modulus of the coating material. Re­ cent investigations, however, have shown that the SAW device has poten­ tial for use in the characterization of polymeric materials. Parameters that

can be determined include the glass transition temperature (Tg), the melt­ ing temperature of crystalline poly­ mers (T m ), thermal expansion coeffi­ cients, and thermal relaxation activa­ tion energies (5). The SAW device pro­ vides a rapid, sensitive, and inexpensive alternative to existing methods. Future research will likely follow several paths. New SAW device config­ urations (e.g., resonators) and packag­ ing approaches offer potential for re­ ducing noise and drift. Different types of acoustic waves can be developed for chemical sensing in both liquid and va­ por phases. Continued vapor/coating interaction research should yield new coating formulations that will expand the range of analytes accessible to SAW device technology. Further development of pattern rec­ ognition algorithms should also strengthen the power of array sensors. Attempts are being made to use mod­ ern silicon micromachining techniques to facilitate total system miniaturiza­ tion of valves and pneumatic hardware often used to support the SAW sensor "chip." The successes of these efforts should make chemical sensing with SAW devices a method of choice for chemical analysis in the future.

References (1) Janata, J.; Bezegh, A. Anal. Chem. 1988,60,62 R. (2) Aucouturier, J. L.; Cauhape, J. S.; Destriaue, M.; Hagenmulle, P.; Lucat, C; Menil, F.; Portier, J.; Salardenne, J., Eds.; Proceedings of the International Meet­ ing on Chemical Sensors, July 1987, Bor­ deaux, France. (3) Transducers '87, Proceedings of the International Conference on Solid-State Sensors and Actuators-Transducers; To­ kyo, June 1987. (4) Proceedings of the IEEE Ultrasonic Symposium; Chicago, IL, October 1988. (5) Murray, R. W.; Heineman, W. R.; Jan­ ata, J.; Seitz, W. R. ACS Symposium Se­ ries, in press. (6) White, R. M.; Volltmer, F. W. Appl. Phys. Lett. 1965, 7, 314. (7) Brace, J. G.; Sanfelippo, T. S.; Joshi, S. G. Sens. Actuators 1988,14, 47. (8) Martin, S. J.; Ricco, A. J.; Ginley, D. S.; Zipperian, T. E. IEEE Trans. 1987, UFFC-34(2), 143. (9) Ballantine, D. S., Jr.; Rose, S. L.; Grate, J. W.; Wohltjen, H. Anal. Chem. 1986,58,3058. (10) Grate, J. W.; Snow, Α.; Ballantine, D. S., Jr.; Wohltjen, H.; Abraham, M. H.; McGill, Α.; Sasson, P. Anal. Chem. 1988, 60, 869. (11) King, W. H., Jr. Anal. Chem. 1964, 36(9), 1735. (12) Edmonds, T. E.; West, T. S. Anal. Chim. Acta 1980,117,147. (13) Wohltjen, H. Sens. Actuators 1984, 5, 307. (14) Wohltjen, H. Transducers '87, Pro-

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© 1988, Hamamatsu Corporation