Quantitative characterization of the partitioning of aqueous analytes into a polymer coating

Polymer coatings that are used with guided shear horizontal acoustic wave (SH-SAW) gas sensors are not necessarily optimal for operating in liquid environments due to significant differences between gas-phase and liquid-phase partition coefficients for some analytes. Development of an effective screening methodology for testing potential coatings for use in liquid sensing applications is particularly important for designing sensors for detection of aqueous analytes. Attenuated total internal reflectance Fourier transform infrared (ATR-FTIR) spectroscopy is used to predict the relative magnitude of the responses of a guided shear horizontal surface acoustic wave (SH-SAW) sensor, coated with a poly(dimethyl siloxane) (PDMS) thin film, to a series of aqueous analytes. The ATR-FTIR approach developed here is shown to effectively predict trends in analyte partitioning from water into PDMS and to also provide insight into the local environment of the analyte when combined with density functional theory computational chemistry and the Onsager model for solvent effects. The response of PDMS-coated guided SH-SAW sensors to nonpolar analytes exhibits an apparently anomalous positive frequency shift that is attributed to having a significant viscoelastic effect in addition to the mass-loading contribution. Sensor responses are linear with respect to analyte concentration.