Sol-gel based fiber optic pH nanosensor: Structural and sensing properties

Evanescent wave absorption based PCS (plastic clad silica) fiber optic pH sensor is constructed by encapsulation of indicator dyes in the heterogeneous inorganic hybrid silica-titania nanomatrix in the presence of cetyl trimethyl ammonium bromide (CTAB) surfactant by sol-gel method. A nanoporous multilayers (triple layer and six layers) of silica-titania hybrid is deposited on 5 cm uncladed middle portion of the fiber by dip-coating sol-gel technique. The CTAB surfactant expressively improved the host matrix structure and enhanced its porosity. Thermally stable, adhesive and smooth thin nanocladding has been examined using microscopic and thermal analysis. Indicators encapsulated nanomatrices are highly sensitive to pH and show optical output signals in terms of intensity. Therefore, it provides confirmation that interactions between the host matrix and pH-indicator molecules are in good assistance. Furthermore, experimental findings reveal that the sensing species are probably better encapsulated in the matrix and show no leaching of sensing molecules. The prepared nanosensors exhibit a much faster response time because of the material to be sensed diffuses faster into the triple-layer sensors <2 s. These pH sensors are found to have 60 days (2 months) age stability and high reproducibility. A repeatable response over a wide range of pH values between 3 and 11 is obtained.