Fabrication of highly efficient fibre-optic gas sensors using SiO2/polymer nanoporous thin films

A highly porous nano-thin film has been deposited on the optical fibre with the aim to develop a fibre-optic gas sensor. The film was composed of alternate layers of poly(diallyldimethyl ammonium chloride) (PDDA) and silica nanoparticles of 40-50 nm in diameter deposited using the electrostatic self assembly process. As a final step of preparation, the coating was infused with the functional compound of tetrakis-(4-sulfophenyl) porphine (TSPP). Exposure of this material to ammonia induces a change in the absorption spectrum, which can be observed in the transmission spectrum of the coated optical fibre. The ammonia sensor shows a linear sensitivity in the concentration range of 0.1-50 ppm and the sensor response and recovery were within 5 min. The sensor was exposed to different chemical compounds in order to study the sensors selectivity.