Detection of lower hydrocarbons by means of surface plasmon resonance

The selective detection of lower hydrocarbon was investigated by optical chemical sensor based laser-excited surface plasmon resonance (SPR). When an isoprene rubber (IPR) thin film was coated on an Au thin film, the resonance angle changed from 23.1 to 29.3°. Moreover, as an IPR thin film was exposed to lower hydrocarbons, the shifts of the incident angle (Δθ) were observed. Also, when Apiezon-grease (AG) thin film and silicon-grease (SG) thin film were used, Δθ were observed. The sensitivity decreased with an increasing number of carbons in the saturated hydrocarbons. In every cases, when the atmosphere was changed from the lower hydrocarbons to air again, Δθ decreased with time. The time being restored the original incident angle for AG and SG thin films was several minutes and was shorter than that for IPR thin film. But there is some questions about the selective detection of hydrocarbons as Δθ was observed after the introduction of alcohol or acetone.