Label-Free Electrochemical Aptasensor for the Sensitive Detection of Cyanotoxin Anatoxin-a

The sensitive detection of neurotoxin anatoxin-a (ATX) is a necessary to effectively manage and control the treatment of water resources. Here we report the selection of high affinity DNA aptamers targeting ATX for developing an impedimetic aptasensor for ATX for which there are no reported biosensors so far. The dissociation constants (K_d) of the aptamers are in the nanomolar range. The sensor was designed by self assembling of disulfide modified aptamer on a gold electrode. The aptasensor fabrication process was characterized using cyclic voltammetry and electrochemical impedance spectroscopy. Upon ATX recognition to the immobilized aptamer, a marked decrease in the electron-transfer resistance was recorded. This is as a result of the aptamer conformation change which is used as sensor signal. The aptasensor showed a limit of detection of 0.5nM and a wide linear range for ATX concentrations between 1nM and 100nM. The K_d that was calculated from the aptasensor signal showed a lower value implying that the anchoring of the aptamer on the Au surface enhanced its affinity to ATX. The ATX aptasensor showed high stability as well as high specificity against common cynaobacterial toxins. Further biosensor designs will be expected using those aptamers for simple ATX detection