Optical Fibre NO(2) Sensor Based on Lutetium Bisphthalocyanine in a Mesoporous Silica Matrix

In this article, we describe a NO(2) sensor consisting of a coating based on lutetium bisphthalocyanine (LuPc(2)) in mesoporous silica. The sensor exploits the absorption spectrum change of this material which strongly and reversibly decreases in contact with NO(2). NO(2) is measured by following the amplitude change in the reflected spectrum of the coating deposited on the tip of a silica fibre. As diffusion of NO(2) in LuPc(2) is slow, the response time could be slow. To reduce it, the active molecules are dispersed in a mesoporous silica matrix deposited by a sol-gel process (Evaporation Induced Self Assembly) avoiding the formation of large crystals. Doing so, the response is fairly fast. As the recovery is slow at room temperature, the recovery time is reduced by exposure to UV light at 365 nm. This UV light is directly introduced in the fibre yielding a practical sensor sensitive to NO(2) in the ppm range suitable for pollution monitoring.