Selection and Characterization of DNA Aptamers for Electrochemical Biosensing of Carbendazim

This article reports a novel aptamer-based impedimetric detection of carbendazim, a commonly used benzimidazole fungicide in agriculture. High affinity and specificity DNA aptamers against carbendazim were successfully selected using systematic evolution of ligand by exponential enrichment (SELEX). The dissociation constants (K_ds) of the selected DNA aptamers after 10 in vitro selection cycles were characterized using fluorescence-based assays showing values in the nanomolar range. The aptamer which showed the highest degree of affinity and conformation change was used to fabricate an electrochemical aptasensor via self-assembly of thiol-modified aptamer on gold electrodes. The aptasensor exploits the specific recognition of carbendazim by the aptamer immobilized on the gold surface which leads to conformational changes in the aptamer structure. This conformational change alters the access of a ferrocyanide/ferricyanide redox couple to the aptasensor surface. The aptasensor response is thus measured by following the increase in the electron transfer resistance of the redox couple using Faradaic electrochemical impedance spectroscopy. This method allowed a selective and sensitive label-free detection of carbendazim within a range of 10 pg/mL-10 ng/mL with a limit of detection of 8.2 pg/mL. The aptasensor did not show cross reactivity with other commonly used pesticides such as fenamiphos, isoproturon, atrazine, linuron, thiamethoxam, trifluralin, carbaryl, and methyl parathion. Moreover, the aptasensor has been applied in different spiked food matrixes showing high recovery percentages. We believe that the proposed aptasensor is a promising alternative to the currently used methods for carbendazim monitoring.