Fabrication of Humidity-Resistant Optical Fiber Sensor for Ammonia Sensing Using Diazo Resin-Photocrosslinked Films with a Porphyrin-Polystyrene Binary Mixture

Abstract

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.

A Preliminary Study for Tunable Optical Assessment of Exhaled Breath Ammonia Based on Ultrathin Tetrakis(4-sulfophenyl)porphine Nanoassembled Films

“…Regarding CO 2 that can potentially interfere with sensor response, its concentration in breath is extremely high; however, the developed sensor has no response to CO 2 , as previously confirmed [27]. Additionally, no significant sensor responses to other interfering substances present in the exhaled breath, such as acetone and some organic alcohols, have been found [28].…”

Long period grating fibre operating in visible range coated with porphyrin based thin film as an ammonia aqueous sensor

“…DAR-TSPP multilayers were deposited to fibre's and substrate's glass surface as described by Ahmed et. all [5]. The the DAR is positively charged and the TSPP is negatively charged, hence it is possible to deposit them via the layer-by-layer technique using the ionic interaction between them.…”

Sensitive and Reversible Ammonia Gas Sensor Based on Single-Walled Carbon Nanotubes

“…These sensors use the absorption or fluorescence of light to detect ammonia, making them highly selective and sensitive [19]. These sensors can also detect signals through changes in the light scattering pattern [20]. Maierhofer et al described the development of optical ammonia sensors based on fluorescent aza-BODIPY dyes, suitable for environmental, bioprocess, and reaction monitoring, capable of detecting ammonia levels of the order of 1μg/L [21].…”