Intrinsic Fiber Optic pH Sensor for Measurement of pH Values in the Range of 0.5–6

The development, design, and evaluation of an intrinsic optical fiber pH sensor for low pH values (in the range of 0.5-6) based on fluorescence from a novel coumarin dye, which is covalently immobilized onto the end surface of an optical fiber is described. The sensor provides a rapid response (of approximately 25 s) over this pH range of 0.5-6.0, showing with very good stability over a period of several months. The sensor has also demonstrated insensitivity to ionic strength and excellent photostability through a series of laboratory tests.