Fiber optic ammonia sensor using Bromocresol Green pH indicator

In this work we report a fiber optic sensor for the detection of ammonia at low level concentrations by means of the utilization of as colourimetric pH indicator, Bromocresol Green (BCG), attached to the optical fiber. BCG is immersed into a hydrophobic and gas permeable polyurethane film named Tecoflex^® that acts as a trapping matrix. Highly reproducible and reversible fiber optical sensors have been obtained employing a simple and quick dip-coating fabrication process. BCG pH indicator takes advantage of the basicity of ammonia and exhibits a wide spectral response (500 nm-750 nm) while showing recovery times of less than 15 s. On the other hand, the hydrophobicity of the Tecoflex^® film provides additional advantages, such as operation even in extremely dry environments, efficient transport and leakage or detachment of the BCG pH indicator prevention. The combination of the BCG pH indicator and Tecoflex^® film provides a reliable and robust fiber optic ammonia gas sensor suitable to be used in real applications.