EQCM Studies of Paraquat on Gold Electrode Modified with Electropolymerized Film

This study presents a polyviologen (PV) modified gold/quartz electrode to detect paraquat (MV2+) by electrochemical quartz crystal microbalance (EQCM) method. Some electroactive viologens (V2+) reside in the electropolymerization achieved in pH 4.2 Britton-Robinson (BR) buffer solution containing soluble viologen oligomer. Closely examining the EQCM and cyclic voltammetry (CV) results reveal that V2+ binds in the PV film and is electroreduced to form its relatively hydrophobic cation radical (V+.), which may cause the anions and hydrated water originally incorporated in the PV layer to be expelled. Moreover, while the negative potential is scanned over −0.55 V, the dissolved MV2+ is reduced through V+. to form its corresponding cation radical (MV+.) and then becomes a dimer with the bound V+. among the PV layer. According to our results, such dimerization possesses good reversibility so that the resonant frequency of the subsequent PV modified Au/quartz electrode can return to its initial value under the potential scanning within an appropriate region (i.e., from 0 to −0.7 V) and oxygen-free condition. Moreover, a linear calibration plot for detecting MV2+ is also obtained in the range from 0 to 1.2 mM, having a detection limit of 0.1 mM.