A chemical sensor with improved selectivity using a modified-electrode QCR

Quartz Crystal Resonators (QCR) coated with sensitive polymer materials with different polarities are being investigated for the detection of volatile organic compounds (VOC), based on changes in dielectric properties of the coatings. Modified-electrode QCRs, known to have strong electric fringing fields associated with the sensing surface, are used and efficient probing of the coating dielectric properties is achieved. Enhanced selectivity is obtained via measurements of changes in the parallel-resonant frequency, f_p a measure of the dielectric properties. The results showed that the sensor signals are completely reversible and reproducible at room temperature. Detection of less than 1 ppm of nitrobenzene in air has been demonstrated. It is seen that the measurements of the parallel-resonant frequency, f_p, together with the series resonant frequency, f_p, provide additional information which can be used to implement sensors/sensor arrays with significantly improved selectivity