Highly selective surface plasmon resonance sensor for NO2

Changes in the surface plasmon resonance (SPR) of a 45 nm thick gold film thermally evaporated onto one face of a BK7 glass prism, have been used to detect nitrogen dioxide (NO₂). The intensity of the reflected light decreases linearly with the concentration of gas, the change being 0.1%, per 1 ppm of NO₂ with a response time of ~30 s for adsorption and 30-40 s for desorption. The process is highly selective and other gases, e.g. NH₃, H₂, CO, CO₂, SO₂, HCl, C1₂ and H₂S, have little or no noticeable effect on the SPR at concentrations of 100 ppm. It is also reversible by flushing with air and the NO₂ sensor showed only a 10% deterioration in the SPR response after 1500 adsorption/desorption cycles