Fiber optic pH sensor based on mode-filtered light detection

A novel mode-filtered light fiber optic pH sensor was developed by inserting an optical fiber immobilized with a pH-sensitive indicator into a fused-silica capillary. In the experiment, two different indicators, bromocresol green and cresol red, had been used for pH sensing. The sensor immobilized with indicator bromocresol green or cresol red showed the response to pH in the range of 2.0–8.0 and 9.0–13.0, respectively. The sensors showed good reproducibility and reversibility within the dynamic pH range and the response times (t95%) were within 120 s. The interference of some common cations to the sensors was investigated and K+ and Pb2+ were the potential interferents to the sensor immobilized with bromocresol green.