Polymer coated QCM sensor with modified electrode for the detection of DDVP

A quartz crystal microbalances (QCMs) based sensor was fabricated by modifying the geometry and size of the electrode to detect organophosphorus pesticide o,o-dimethyl-o-2,2-dichlorovinyl phosphate (DDVP). Both conductive and non-conductive polymers were characterized on the surface of the modified QCM electrode. Operating at the resonant frequency ranging from 10 to 20 Hz, the QCMs coated with non-conductive polymers, polyvinyl alcohol (PVA) and poly (acrylic acid) (PAA), were sensitive to DDVP. The results showed that the resonant frequency range of QCMs increased by the coating with conductive polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) and a copolymer of PEDOT with poly(styrene sulphonic acid) (PEDOT/PSS), which was from 20 to 115 Hz and 18 to 60 Hz, respectively. The mechanism and corresponding equivalent circuit model of the QCM-based sensor were presented. The capacitance was calculated in the range of 0.199–0.194 pF for the PEDOT/PSS film and 0.198–0.187 pF for the PEDOT film. In the range of 6.5–32.5 ppm DDVP concentration, the relationship between the response of the sensor coated with PEDOT and the concentration was linear. The relative standard deviation of the modified sensor was less than 5%.