Surface Acoustic Wave Sensor Platforms Research Articles

Analysis of the absorption kinetics for the detection of parathion using hybrid organic/inorganic coating on SH-SAW devices in aqueous solution

Organophosphate pesticides (OPs) have been found as contaminants in surface and ground waters, soil, and agricultural products. Because OPs are toxic compounds, monitoring of OPs in groundwater is necessary to allow for real-time remediation. Various types of polymer-coated sensors are being investigated for the rapid detection/monitoring of OPs in groundwater. The focus of this paper is on analyzing the sensor response of an acoustic wave device for the detection of organophosphate pesticides in aqueous solutions to determine whether the analyte absorption is penetration limited or diffusion limited. In this work, kinetic studies for the absorption of organophosphates (parathion-methyl, parathion, and paraoxon) from aqueous solutions into a hybrid organic/inorganic chemically sensitive layer [bisphenol A–hexamethyltrisiloxane (BPA-HMTS)] coating are conducted using guided shear horizontal surface acoustic wave sensor platforms on 36° rotated Y-cut LiTaO3. The objective of the studies is to provide an understanding of the underlying physics of the sensor response. The sensor data are analyzed within the context of two absorption models: penetration-limited and diffusion-limited absorptions. It is shown that the absorption process is rate-limited by penetration with a concentration independent absorption time constant or mass transfer coefficient. The absorption time constants for parathion-methyl, parathion, and paraoxon are calculated. It is seen that even though paraoxon is only 3.8% smaller (by volume) than parathion, its absorption time constant (∼10.5±2.1min) is, for the same coating thickness, at least 50% faster than parathion (∼32.5±1.6min). On the other hand, parathion-methyl, which is 9.5% smaller than paraoxon, exhibited about the same absorption time (∼8.3±0.5min) as paraoxon. This difference in transient information can be used to improve analyte recognition (between parathion/paraoxon and parathion/parathion-methyl).

A microfluidic surface acoustic wave sensor platform: Application to high viscosity measurements

Acoustic Love wave oscillators offer a great potentiality to integrated viscosity measurements thanks to a high sensitivity and the lack of moving parts. The main limitation is insertion losses that increase with viscosity. To overcome this limitation, this paper reports the use of microfluidic techniques with a poly(dimethylsiloxane) (PDMS) chip bonded on the Love wave device. Liquid flows of aqueous glycerol solutions up to 0.939 Pa s (939cP, 98% glycerol) have been tested in oscillator mode. These results are promising for the viscoelastic study of viscous liquids. Modelisation using the classical perturbation theory is discussed.

Hydrogen‐bond acidic polyhedral oligosilsesquioxane filled polymer coatings for surface acoustic wave sensors

AbstractA series of novel polyhedral oligosilsesquioxane nanofiller compounds functionalized with hydrogen‐bond acidic sensor groups was prepared, characterized by IR, 1H‐, 13C‐ and 29Si‐NMR, and MALDI‐TOF MS, and formulated into polymer coatings for 500 MHz surface acoustic wave sensor platforms. Sensor responses to the explosives simulant dinitrotoluene and to the nerve agent simulant dimethyl methylphosphonate were studied, and the performances of the polyhedral oligosilsesquioxane formulations were compared with those of conventional hydrogen‐bond acidic linear surface acoustic wave sensor polymers carrying the same sensor groups. The polyhedral oligosilsesquioxane formulations gave good initial responses to the simulants, maintained 40–65% of their original response over a period of 6 months and maintained their sensitivity down to a simulant vapor concentration of 1 ppb v. The surface compositions of the surface acoustic wave sensor coatings were characterized by sum frequency generation spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

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

Direct chemical sensing in liquid environments using polymer-guided shear horizontal surface acoustic wave sensor platforms on 36 degrees 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.