Enhancing detection of nitroaromatic vapors by utilizing polymer coatings on quartz crystal microbalances having strong dipoles

A novel class of PDMS based polymers containing azobenzene side chains were synthesized and evaluated as coatings for quartz crystal microbalance (QCM) based sensors to detect nitroaromatic vapors. The polymers contain functional groups (p-substituted azobenzene moieties and hydroxyl groups) that can interact with compounds with large dipole moments such as nitroaromatic chemicals through a combination of permanent dipole-dipole interactions and hydrogen bonding. A QCM sensor array was prepared by coating different polymers onto the surface of a quartz crystal and evaluating the response of the each coating to saturated vapors of a variety of analytes such as toluene, octane, 2-nitrotoluene, nitrobenzene, and 2,4 dinitrotoluene. The incorporation of azobenzene moieties in the polymer structure increased the sensor response towards the nitroaromatic analytes. Pattern recognition techniques such as principal component analysis (PCA) and decision tree learning methods were applied to evaluate the sensor response and predict analyte identity. A classification accuracy of 96% was obtained using classification and regression trees (CART) based learning. This novel approach opens new possibilities in ultrasensitive detection of chemical vapors with significant dipole moments.