Physical discrimination of amine vapor mixtures using polythiophene gas sensor arrays

Sensor arrays are extremely powerful sensing platforms because the use of an array enables more discrimination power than achievable by using a single sensor. Unfortunately most current research on gas or vapor sensor arrays focuses on distinguishing between classes of molecules. For many attractive applications, such as environmental monitoring or food spoilage detection, it is important to discriminate within each class of molecule. We demonstrate simple yet powerful arrays that can discriminate vapor molecules based on their size and the molecular arrangement. Gas sensing is accomplished using polythiophene-based thin film transistors (TFTs) that respond to analyte vapors with changes in electrical behavior. By varying the side chain of the polythiophene molecule as well as adjusting the thickness of the polythiophene films, size discrimination of amine vapors can be accomplished using small arrays of polythiophene transistors. With these arrays, size discrimination is even possible with mixtures of amine vapors. Grazing incidence X-ray diffraction (GIXD) shows that the film orientation and plane spacings depend on the side chain length of the polythiophene, and these structural differences are used to explain the sensor behavior.