Deposition of SiO2/polymer nanoporous thin films on long-period grating (LPG) optical fibres and dramatic enhancement of the resonance bands

A nano-assembled porous thin film, deposited using the layer-by-layer method and infused with a functional compound, is used for the development of a highly sensitive fibre-optic ammonia sensor. Sensor fabrication involves a 2-stage process: firstly the deposition of the basic porous thin film (poly(diallyldimethylammonium chloride)/SiO₂) over a long period grating written in optical fibre, followed by infusion of a porphyrin compound (tetrakis-(4-sulfophenyl)porphine, TSPP), into the porous film. The device shows high sensitivity to ammonia (ca. 1 ppm) when immersed into an aqueous solution.