Effect of Humidity on Nh3 Gas Sensitivity of Nafion R /WO3 Sensing Structure of Spr Sensor

The paper presents an optical sensor that permits to detect and to measure the concentration of ammonia gas in a gaseous medium and the effect of humidity on the NH3 detection capability of sensing structure of optical sensor was also investigated. The presence of water vapour, functioning as the interference gas, led to the lowering of the NH3 response of the sensor in a humid atmosphere. An optical sensor of ammonia gas, based on the surface plasmon resonance (SPR) method has been investigated. The surface plasmon resonance (SPR) is very sensitive, and so is the optical technique used in chemical sensing. NafionŽ/WO3 stack films on plasmon active Au film was used as the sensing structure of SPR sensor. The gold layer was coated by means of vacuum evaporation on a BK7 substrate. The thickness of Au was about 50 nm. The sensing structures were coupled on immersion oil with a prism coupler. Although NafionŽ film had hydrophilic character absorbs 22% by weight of water, the influence of humidity on the SPR sensor response was not as large as expected due to construction of the sensing structure. A change of the intensity of light of the plasmon dip was observed when chemical active stack films (Nafion R/WO3) was exposed to varying concentrations of NH3 in a dry and humid atmosphere. Optical ammonia gas SPR sensor display a very fast response time and a fast regeneration time at room temperature not only in a dry atmosphere, but also in a humid atmosphere.