Sol-gel Film Doped with Bromopyrogallol Red as a Highly Sensitive Sensing Element for a new pH Optical Sensor

Bromopyrogallol red (BPR) pH-indicator was incorporated into a sol-gel silica matrix and used for sensing pH as a solid indicator. Entrapment of BPR into silica matrix was performed by the acid-catalyzed sol-gel reaction of tetraethylorthosilicate (TEOS) and the BPR indicator. The immobilized BPR shows better behavior than its solvated form in solution. No leaching was observed during the repetitive experiments, indicating that BPR molecules were strongly trapped into the silica matrix. At optimal condition, the sensor responded rapidly to pH changes in a range of 2.33-9.42 with the response time about a minute. The equation A = 0.081 + 0.038 pH with R2 = 0.992 was obtained by regression of linear portion of the calibration curve plot of the sensor responses at various pH values. This sensor was highly sensitive, quite reversible and had a long lifetime of over 10 months.