Aptamer-conjugated gold nanoparticles/ reduced graphene oxide for electrochemical detection of malathion

The widespread use of organophosphorous (OP) compounds in environment has raised serious human health and environmental concerns. The OPs are commonly used as pesticides and insecticides, but also display potential to be employed as chemical warfare agents (CWAs) by terrorist. Thus, the development of chemical sensor with high sensitivity and selectivity towards OPs is of vital importance. Electrochemical sensor is one of the most useful techniques that has been reported for the detection of OPs due to its stability, potential to be miniaturized for on site detection, and simple measurement procedure. Herein, we have developed an electrochemical sensor for detection of malathion that employs gold nanoparticles (AuNPs) decorated reduced graphene oxide (rGO) modified on screen printed carbon electrode (SPCE) as the sensing platform. Graphene oxide was electrochemically reduced on SPCE and further modified with AuNPs to produce AuNPs/rGO-modified SPCE which was then utilized for the immobilization of thiolated DNA aptamer by self-assembly method. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron micrograph (SEM) were utilized to show the successful surface modification of SPCE. The detection was carried out by using EIS and the result shows that the value of charge transfer resistance increased upon binding of malathion to the aptamer-modified electrode indicating the successful formation of malathion-aptamer complex that blocks the electron transfer. The sensor also demonstrated good selectivity for malathion against other OP compounds such as DMMP, paraoxon and phorate. This proposed electrochemical sensor provides a sensitive and selective detection of malathion which can be potentially used for application in real samples.