The present paper describes a novel and simple aptamer-based strategy for label-free determination of atrazine (ATZ) in solutions using a glassy carbon electrode (GCE) modified with chitosan (CS) and a nanocomposite film composed of multiwalled carbon nanotubes (f-MWCNs) and graphene oxides (GO). The chitosan and nanocomposite film provide the appropriate sites for the better attachment of aptamer owing to the presence of amino and carboxyl functional groups. In order to increase the specificity of the proposed sensor, the NH2- terminal aptamer was immobilized at the surface of f-MWCNTs-GO/CS nanocomposite through the formation of chemical bonds between the amino groups of the aptamer and functional groups of the nanocomposite by using the gluteraldehyde (GLA) as a cross-linker. Various electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were utilized to characterize the changes of the surface of the modified electrode in each step. In the presence of atrazine, the aptamer molecules selectively combine with the target molecules at the electrode surface which results in a decrease in the current intensity of DPV and CV electrochemical signals. Under the optimized experimental conditions, the presented aptasensor revealed a wide linear range of 1 to 250 nM with a low detection limit of 0.06 nM. In addition, the practical application of the fabricated aptasensor for the measurement of the low concentration of atrazine was tested in real samples, and the satisfactory results were obtained.

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