A Fluorescence Intensity Ratiometric Fiber Optics-Based Chemical Sensor for Monitoring pH

Accurate determination of pH is essential, yet a single technology is relied upon for almost all pH measurements. Here, a new optical pH sensor is described. Two highly photostable fluorescent dyes with a polymerizable side chain are incorporated into a composite polymer that allows for fast transport of protons. A pH-responsive dye and a reference dye with limited response to pH are used, thus allowing for determining pH using a ratiometric fluorescence intensity response. The sensor material-dyes covalently attached in the composite polymer-is deposited on a polycarbonate hemiwicking substrate, and immobilized on the inside of a shaker flask. In this manner, two robust pH optodes with pK(a) values of 5.30 and 6.11 are prepared. The pH-responsive composite materials are addressed using fiber optics, and the response is recorded on a fiber spectrometer. The optodes are shown to have low drift, fast response time, no leachables, and the sensor is shown to work in heterogeneous media exemplified with coffee, beer, and cola.