Nitrogen dioxide vapor detection using poly-o-toluidine

We describe a flexible, lightweight, reversible NO2 vapor sensor based on resistance changes of a thin film of a doped conducting polymer, poly-o-toluidine, deposited on plastic substrates. Unlike the irreversible signals typically observed in organic films, signal reversibility in the concentration range 100–10 ppm is readily achieved using a short burst of UV irradiation at room temperature in ambient air without the aid of heating or pump down cycles. Interestingly, signal response is dependent on the organic solvent used to cast the polymer film with dipolar aprotic solvents yielding films showing a strong response. There are striking differences in electrical and electronic properties including morphology of films cast from different solvents. This phenomenon is traced to polymer chain conformation in solution that is preserved in the solid state (cast film) which opens a new structural vector to tailor sensor response and selectivity. This study also expands the use of conducting polymers for the detection of vapors that were previously believed to be chemically too aggressive.