Polyaniline based optical pH sensor

Thin layers of polyaniline are suitable to measure optically the pH in the range of 2–12 in the near infrared region. The deposition of such layers is strongly facilitated by the use of solution-processable polyaniline. Previously unconsidered hysteresis effects are observed in the titration curves. Testing the sensor layers over a period of 300 h and up to 500 titration cycles revealed excellent reproducibility and stability. An absorbance drift lower than 1% per day (corresponding to about 30 titration) was observed.