Spectroscopic and computational investigation of polymer coatings and analyte systems for use with guided shear horizontal surface acoustic wave (SH-SAW) sensors for liquid phase detection.

摘要

The goal of this work is to explore technology related to the design of field-portable, real-time sensors for detection of hazardous compounds in liquid environments---specifically the design and function of chemically sensitive polymers as coating materials for guided shear horizontal surface acoustic wave (SH-SAW) sensor devices in liquid phase detection. Through fundamental investigation of the interactions of polymer coatings with model analytes, and the effects of physical properties of coating materials on sensor response, insight is gained which may be applied toward the development or selection of coatings that target specific toxins or classes of toxins. Attenuated total internal reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was used for the investigation of sorption of aqueous solutions of analytes into polymer coatings. A series of simple model polymers: poly(dimethylsiloxane) (PDMS), poly(epichlorhydrin) (PECH), and poly(isobutylene) (PIB) films and analytes: aqueous solutions of ethylbenzene, xylenes, toluene, and nitrobenzene were used to evaluate the use of ATR-FTIR spectroscopy as a screening tool for sensor development. The ratios of integrated infrared absorption bands provided a simple and efficient method for predicting trends in partition coefficients. Responses of polymer-coated guided shear horizontal surface acoustic wave (SH-SAW) sensor platforms to the series of analytes, using polymer coatings with similar viscoelastic properties, were consistent with ATR-FTIR predictions. Guided SH-SAW sensor responses were linear in all cases with respect to analyte concentration in the tested range. Comparison of ATR-FTIR data with guided SH-SAW sensor data identifies cases where mass loading is not the dominant contribution to the response of the acoustic wave sensor. Changes in polymer viscoelasticity, estimated from the loss of the guided SH-SAW signals, were used to theoretically assess the overall contribution of mass and modulus changes to PIB-coated devices. The theoretical predictions show excellent agreement with the experimental sensor response. ATR-FTIR and UV-Visible spectroscopy were used to investigate the effect of the local environment on the spectral changes of nitrobenzene, 4-nitrophenol, and 2,6-dinitrotoluene. These methods, coupled with computational chemistry, provided additional insight into analyte/polymer interactions.