5 Bromophenol Blue Thin Film Coated Fiber Optic Response Towards pH Sensing

The fabrication and characterization of a fiber optic pH sensor based on the evanescent wave absorption is presented in this paper. The sensor is prepared by coating the immobilized indicator in a sol-gel thin film onto the uncladded middle portion of a multimode plastic clad silica (PCS) fiber. The evanescent wave is used to selectively excite the indicator molecules within the fiber cladding for sampling the aqueous media surrounding the fiber. Changes in the pH of the analyte are detected by measuring the absorption spectrum of the sol-gel cladding in the sensing region of the optical fiber. pH buffer 1 - 14 were used to examine the response of the sensor. The sensor response and its dynamic range are reported for bromophenol blue (BPB) dye. The intensity of the absorption measured in the 470 - 850 nm spectral range has been found to increase as the pH value increases. The performance of the device is evaluated in terms of the results obtained during actual measurements.