Voltammetric determination of paraquat at DNA–gold nanoparticle composite electrodes

A novel electroanalytical method for the detection of paraquat using DNA modified gold nanoparticles immobilized at a gold electrode is demonstrated. The electrode surface was first modified using the self-assembly of gold nanoparticles (NPs) followed by the simple adsorption of DNA onto the NPs, which was straightforward, fast and cost effective. The DNA–nanoparticle composite sensor was then characterized in terms of electrochemical responses both in the absence and in the presence of paraquat using cyclic voltammetry, differential pulse voltammetry and square wave voltammetry. The DNA–NPs composite electrode proved to work adequately as a biosensor for the quantitative analysis of paraquat concentrations, taking advantage of utilizing both the modified gold nanoparticles and the interaction between DNA with paraquat molecules. In addition, the NPs modified electrode demonstrated good sensitivity and stability towards the first reversible reduction step of the double charged paraquat ion. Good linearity between paraquat concentration and peak current was observed for the concentration range of 5.0 × 10−6 to 1.0 × 10−3 M when using differential pulse voltammetry. The use of modified electrodes improves the performance of the biosensor in the presence of interfering species in particular when square wave voltammetry is used.