Optical fiber ammonia sensing probes using reagent immobilized porous silica coating as transducers

Optical fiber probes for sensing ammonia vapor in gas samples and trace ammonia dissolved in water were developed. An organic dye was immobilized in a porous silica membrane with a sol–gel process as an ammonia indicator. The organic dye immobilized porous silica membrane was coated on the surface of a bent optical fiber core. The coated optical fiber probe was tested for sensing ammonia vapor in gas samples using fiber optic UV–vis absorption spectrometry. An optical fiber ammonia vapor probe with a PDMS protection coating was tested for sensing trace ammonia in water samples. The characteristics of the bent optical fiber probes for sensing ammonia vapor in gas samples and trace ammonia in water samples were studied. Test results indicate that the optical fiber ammonia vapor probe can detect ammonia vapor in a gas sample down to 13 ppb, and the PDMS protection coated optical fiber ammonia probe can detect ammonia in a water sample down to 5 ppb. Low cost, simple structured fiber optic sensors for detecting ammonia vapor in gas samples and trace ammonia dissolved in water can be developed based on the result reported in this paper.