Trace dissolved ammonia sensor based on porous polyelectrolyte membrane-coated thin-core fiber modal interferometer

A fiber-optic ammonia sensor based on a thin-core fiber modal interferometer (TCFMI) is fabricated and evaluated. The fast response to ammonia is achieved via the construction of poly(acrylic acid) (PAA) and poly(allyamine hydrochloride) (PAH) nanoporous films on the side surface of the TCFMI using the layer-by-layer (LbL) assembly technique. The fabricated sensing nanocoating is characterized by FT-IR spectrometer, UV-vis absorption spectroscopy, surface profiler, and scanning electron microscopy (SEM). Porous structure is beneficial to the diffusion of ammonia molecules through the multilayers. The TCFMI with a 10-cycle PAH/PAA nanoporous film sensor presented an excellent reproducibility with a fast response time to ammonia. The optimal detection range of this sensor is around 1-260 ppm with a low limit of detection (LOD).