Free-grown polypyrrole thin films as aroma sensors

We describe the use of free-grown thin polypyrrole films as fast response sensors of volatile compounds. Using a variety of dopants, the polymeric films were prepared directly on conducting glass substrates. Ultraviolet-visible and near infrared regions absorbance measurements were used to investigate the deposition process and the doping level of the films. We identify the polymerization time as the fundamental parameter for determining the characteristics of the sensor, since it affects not only the final level of doping but also the kinetics of adsorption and the homogeneity of the films. Electrical measurements confirmed the sensitivity and selectivity of the sensors to the presence of vapors of volatile organic solvents. A fast response time was observed in all cases, although the intensity of the corresponding signal was in general larger for the polar than for the nonpolar compounds. The sensitiveness of the sensors towards simple organic solvents is analyzed as well as their reproducibility and the aging effect upon the specific responses.