SUMMARY
The development of an evanescent wave optical fiber sensor modified with an organic–inorganic hybrid nanoporous thin film for the detection of organic solvent vapors was demonstrated. The optical fiber with a core diameter of 200 μm was bent into U‐shape to enhance the penetration depth of light transferred into the evanescent field, and modified with a multilayered thin film of poly (allylamine hydrochloride) and silica nanoparticles (PAH/SiO2)n, via layer‐by‐layer (LbL) film deposition. The mesoporous film structure led to higher molecular diffusion and the highest selectivity to methanol among the six alcohols and water, which were used as target analytes, by the aid of tetrakis (4‐sulfophenyl) porphine (TSPP) infused inside the film.
Ammonia gas sensors were fabricated via layer-by-layer (LbL) deposition of diazo resin (DAR) and a binary mixture of tetrakis(4-sulfophenyl)porphine (TSPP) and poly(styrene sulfonate) (PSS) onto the core of a multimode U-bent optical fiber. The penetration of light transferred into the evanescent field was enhanced by stripping the polymer cladding and coating the fiber core. The electrostatic interaction between the diazonium ion in DAR and the sulfonate residues in TSPP and PSS was converted into covalent bonds using UV irradiation. The photoreaction between the layers was confirmed by UV-vis and Fourier transform infrared spectroscopy. The sensitivity of the optical fiber sensors to ammonia was linear when exposed to ammonia gases generated from aqueous ammonia solutions at a concentration of approximately 17 parts per million (ppm). This linearity extended up to 50 ppm when the exposure time (30 s) was shortened. The response and recovery times were reduced to 30 s with a 5-cycle DAR/TSPP+PSS (as a mixture of 1 mM TSPP and 0.025 wt% PSS in water) film sensor. The limit of detection (LOD) of the optimized sensor was estimated to be 0.31 ppm for ammonia in solution, corresponding to approximately 0.03 ppm of ammonia gas. It is hypothesized that the presence of the hydrophobic moiety of PSS in the matrix suppressed the effects of humidity on the sensor response. The sensor response was stable and reproducible over seven days. The PSS-containing U-bent fiber sensor also showed superior sensitivity to ammonia when examined alongside amine and non-amine analytes.
The development of an evanescent wave optical fibre (EWOF) sensor modified with an organic-inorganic hybrid nanoporous thin film for alcohol vapor detection was demonstrated. The optical fibre with a core diameter of 200 μm was bent into U-shape probe optic fibre to enhance the penetation depth of light transferred into the evanescent filed. The bended region of the fibre was modified with a multilayered thin film of poly(allyamine hydrochloride) and silica nanoparticels, (PAH/SiO2)n, by a layer-by-layer (LbL) film deposition technique, followed by infusion of tetrakis(4-sulfophenyl)porphine, TPPS. The mesoporous film structure showed high sensitivity and selectivity to methanol by the aid of the TPPS infused inside the film. The optical sensor response was reversible and reproducible over many times of exposures to analytes, which was caused by the change in refractive index (RI) of the film.
SUMMARY
The development of an evanescent wave optical fiber sensor modified with an organic–inorganic hybrid nanoporous thin film for the detection of organic solvent vapors was demonstrated. The optical fiber with a core diameter of 200 μm was bent into U‐shape to enhance the penetration depth of light transferred into the evanescent field, and modified with a multilayered thin film of poly (allylamine hydrochloride) and silica nanoparticles (PAH/SiO2)n, via layer‐by‐layer (LbL) film deposition. The mesoporous film structure led to higher molecular diffusion and the highest selectivity to methanol among the six alcohols and water, which were used as target analytes, by the aid of tetrakis (4‐sulfophenyl) porphine (TSPP) infused inside the film.
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