Analysis of Liquid-Phase Chemical Detection Using Guided Shear Horizontal-Surface Acoustic Wave Sensors

Abstract

Direct chemical sensing in liquid environments using polymer-guided shear horizontal surface acoustic wave sensor platforms on 36° rotated Y-cut LiTaO3 is investigated. Design considerations for optimizing these devices for liquid-phase detection are systematically explored. Two different sensor geometries are experimentally and theoretically analyzed. Dual delay line devices are used with a reference line coated with poly (methyl methacrylate) (PMMA) and a sensing line coated with a chemically sensitive polymer, which acts as both a guiding layer and a sensing layer or with a PMMA waveguide and a chemically sensitive polymer. Results show the three-layer model provides higher sensitivity than the four-layer model. Contributions from mass loading and coating viscoelasticity changes to the sensor response are evaluated, taking into account the added mass, swelling, and plasticization. Chemically sensitive polymers are investigated in the detection of low concentrations (1−60 ppm) of toluene, ethylbenzene, and xylenes in water. A low-ppb level detection limit is estimated from the present experimental measurements. Sensor properties are investigated by varying the sensor geometries, coating thickness combinations, coating properties, and curing temperature for operation in liquid environments. Partition coefficients for polymer−aqueous analyte pairs are used to explain the observed trend in sensitivity for the polymers PMMA, poly(isobutylene), poly(epichlorohydrin), and poly(ethyl acrylate) used in this work.

Liquid-Phase Chemical Sensing Using Lateral Mode Resonant Cantilevers

“…18 Generally, for environmental sensors, limits of detection in the low parts per billion concentration range are dictated by the exposure limits outlined by the EPA. 1 While state-of-the-art acoustic wave devices may achieve limits of detection in the low parts per billion range, 23 their fabrication is more elaborate as they require piezoelectric materials to be incorporated into the fabrication processes. 24 Consequently, the present study takes advantage of cantilever-based resonant sensor platforms fabricated by complementary metal oxide semiconductor (CMOS) compatible processes, yet yielding parts per billion range detection limits for addressing volatile organics in water at environmentally relevant concentration levels.…”

Online Drift Compensation for Chemical Sensors Using Estimation Theory

“…Because it is difficult to directly measure the sensor baseline during exposure, it must be estimated using the information in the sensor output. Reference sensors can be used to try to measure the baseline signal [3]. However, because the reference sensor, by definition, has been modified so that it does not respond to the analyte, it likely does not have a baseline identical to that of the sensing line.…”

Sorption-induced static bending of microcantilevers coated with viscoelastic material

“…The steady-state elongation can be calculated using the partition coefficient, which can be obtained from an independent experiment. 21,26 If a steady-state elongation of 1.0% is assumed for the CD coating exposed to the dichloromethane and 1.1% is assumed for the CD coating exposed to the trichloroethylene ͑typical volume expansions for the absorption of analytes into chemically sensitive coatings vary between 1% and 5%͒, 26 the calculated unrelaxed and relaxed modulus for the CD coating are found to be around 350 and 70 MPa, respectively.…”