Temperature effect and chemical response of surface acoustic wave (SAW) single-delay-line chemosensors

Abstract

The effects of temperature and chemical vapour absorption on the frequency shift of coated and uncoated SAW single-delay-line oscillators are reported. It is found that the temperature-induced frequency-shift function depends on the nature of the coating of the delay-line surface. It changes from the flat parabolic temperature dependence of an uncoated ST-quartz delay line near room temperature, to a steep, almost linear, curve for polymer-coated delay lines in the same temperature range. The slope of the curves depends on the nature of the polymers. The dual-delay-line concept, where an uncoated SAW delay line is used as a reference element to compensate for the ambient temperature variations, is therefore not universal and should be implemented with great caution. The response of an array of four different SAW delay-line sensors to various chemical vapours is represented by pie charts, visualizing chemical pattern variability that can be used for pattern recognition. The frequency shifts are correlated with calculated theoretical partition-coefficient values, based on thermodynamic parameters and regular solution theory. It is shown that this approach may be used to predict the interaction between the polymer and a specific target chemical vapour. A simple method for a preliminary design of a SAW chemosensor is thus suggested.