High Sensitive Ammonia Detection in Water With Fabry-Perot Interferometers

This letter presents the development and characterization of a Fabry-Perot interferometer (FPI) for the detection of dissolved ammonia. The FPI cavity is obtained by the alignment of two single mode fibers (SMFs), where a mixture of ultraviolet (UV) curable resin and Oxazine 170 perchlorate is positioned in the gap between both SMFs. The sensor operation principle is based on the chemical reaction between the dissolved ammonia and the Oxazine 170 perchlorate. Such reaction leads to the refractive index variation in the FPI cavity, which results in a wavelength shift of the reflected spectrum. The water absorption and temperature effects in the sensor response are characterized. Such characterizations demonstrate that a good sensor performance is achieved when it is submerged in aqueous solutions for about one hour (to enable the water absorption) and at controlled temperature conditions. Then, the FPI sensor is submerged in ammonia solutions with concentrations ranging from 0 to 700 ppb (in 100 ppb steps). Results show a reversibility of the proposed sensor and a high sensitivity of 4.3 pm/ppb (4.3 nm/ppm). Thus, the proposed sensor can be used on the detection of low concentrations of ammonia (in a sub-ppm range) with one of the highest reported sensitivities of ammonia sensors, which makes it suitable for water quality monitoring.This letter presents the development and characterization of a Fabry-Perot interferometer (FPI) for the detection of dissolved ammonia. The FPI cavity is obtained by the alignment of two single mode fibers (SMFs), where a mixture of ultraviolet (UV) curable resin and Oxazine 170 perchlorate is positioned in the gap between both SMFs. The sensor operation principle is based on the chemical reaction between the dissolved ammonia and the Oxazine 170 perchlorate. Such reaction leads to the refractive index variation in the FPI cavity, which results in a wavelength shift of the reflected spectrum. The water absorption and temperature effects in the sensor response are characterized. Such characterizations demonstrate that a good sensor performance is achieved when it is submerged in aqueous solutions for about one hour (to enable the water absorption) and at controlled temperature conditions. Then, the FPI sensor is submerged in ammonia solutions with concentrations ranging from 0 to 700 ppb (in 100 ppb steps). Results show a reversibility of the proposed sensor and a high sensitivity of 4.3 pm/ppb (4.3 nm/ppm). Thus, the proposed sensor can be used on the detection of low concentrations of ammonia (in a sub-ppm range) with one of the highest reported sensitivities of ammonia sensors, which makes it suitable for water quality monitoring.