| Abstract
| - To probe directly the analyte/film interactions that characterize molecular recognition in gas sensors, we recordedchanges to the in situ surface vibrational spectra ofspecifically functionalized surface acoustic wave (SAW)devices concurrently with analyte exposure and SAWmeasurement of the extent of sorption. Fourier transforminfrared external-reflectance spectra (FT-IR-ERS) werecollected from operating 97-MHz SAW delay lines duringexposure to a range of analytes as they interacted withthin-film coatings previously shown to be selective: cyclodextrins for chiral recognition, nickel camphorates forLewis bases such as pyridine or organophosphonates,and phthalocyanines for aromatic compounds. In mostcases where specific chemical interactionsmetal coordination, “cage” compound inclusion, or π-stackingwereexpected, analyte dosing caused distinctive changes inthe IR spectra, together with anomalously large SAWsensor responses. In contrast, control experiments involving the physisorption of the same analytes by conventional organic polymers did not cause similar changes inthe IR spectra, and the SAW responses were smaller. Fora given conventional polymer, the partition coefficients (orSAW sensor signals) roughly followed the analyte fractionof saturation vapor pressure. These SAW/FT-IR resultssupport earlier conclusions derived from thickness-shearmode resonator data.
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