Design and Application of an Optical pH Sensor Based on Thionine Doped Modified Sol–Gel Film

An optical chemical sensor was constructed by incorporating the thionine (TN) dye molecules into a sol–gel silica matrix and it was used for determination the pH of the aqueous solutions. Entrapment of TN dye into the silica matrix was made via an acid-catalyzed sol–gel reaction of tetraethyl orthosilicate (TEOS) and the thionine molecules. The thionine molecules in the immobilized form, showed a different spectral behavior than its solution form. After optimizing the experimental conditions, the fabricated optical sensor showed a fast response to pH changes in the range of 11–13 with a response time about one minute. Also, the obtained results indicate that the proposed pH sensor, has a good reproducibility, reversibility, stability and low leaching and a long lifetime of over 7 months.