Fiber optic based gas sensor with nanoporous structure for the selective detection of NO2 in air samples

A fiber optic based sensor (FOS) system for the selective detection of NO2 in air samples has been developed. In the present design, a signal transduction mechanism based on the spectroscopic changes at the nanopores of a sol–gel element has been utilized. The sensor is prepared by uniformly immobilizing NO2 sensing reagents at the pores during the sol–gel process. This facilitates an easy tailoring of the transducer element to build different optical designs. In the present paper, we describe two different fiber optic sensor designs, which are operating in extrinsic and intrinsic configurations. The extrinsic design is based on the fiber optic transflection probe geometry with its sensor element placed at the distal end of the fiber bundle. A part per billion (ppb) level detection has been achieved with the intrinsic sensor design with an active sol–gel fiber core as a sensor element. The two different optical designs improve the NO2 detection level and sensitivity of detection. The nitrogen dioxide mediated coloration reaction ensures the high specificity of detection when tested in a mixture of gas samples. The test results indicate the potential use of the fiber optic sensor for real time detection of NO2 in air samples.