Fabrication of an optical pH sol-gel sensor based on Thionine dye

In the present work, an optical chemical sensor was constructed by incorporating the thionine (TN) dye molecules (Figure 1) into a sol-gel silica matrix and it was used fordetermination the pH of the aqueous solutions. Entrapment of TN dye molecules into the silica matrix, was made via an acid-catalyzed sol-gel reaction of tetraethyl orthosilicate (TEOS) and the thionine molecules [1]. The thionine molecules in the immobilized form, showed a different spectral behavior than its solution form. Afteroptimization 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. The experimental results, showed that the proposed pH sensor, has a good reproducibility and stability and also a low leaching and a long lifetime of over 7 months. The fabricated optical sensor can be used for pH measurement in real samples.