Fiber optic ammonia sensing employing novel thermoplastic polyurethane membranes

Ammonia gas fiber optic sensors have been fabricated using a commercially available thermoplastic polyurethane resin, Tecoflex®, which entraps a pH indicator that undergoes a color change in presence of ammonia gas. Highly repetitive and reversible sensors have been achieved using simple and short fabrication processes. Evanescent wave absorption has been monitored under exposure to 0.03-1% of ammonia in nitrogen carrier gas, measuring a maximum optical variation of 6 dB at 600 nm. These sensors can work even in extremely dry environments and show recovery times of less than 5 s.