A label-free electrochemical impedance aptasensor for cylindrospermopsin detection based on thionine–graphene nanocomposites

It is important to develop methods to determine cylindrospermopsin (CYN) at trace levels since CYN is a kind of widespread cyanobacterial toxin in water sources. In this study, a label-free impedimetric aptasensor has been fabricated for detecting CYN. In this case, the amino-substituted aptamer of CYN was covalently grafted onto the surface of the thionine–graphene (TH–G) nanocomposite through the cross-linker glutaraldehyde (GA). The reaction of the aptamer with CYN was monitored by electrochemical impedance spectroscopy because the CYN induced conformation change of the aptamer can cause a remarkable decrease of the electron transfer resistance. Under optimum conditions, the aptasensor exhibits high sensitivity and a low detection limit for CYN determination. The CYN can be quantified in a wide range of 0.39 to 78 ng mL−1 with a good linearity (R2 = 0.9968) and a low detection limit of 0.117 ng mL−1. In addition, the proposed aptasensor displays excellent stability, reusability and reproducibility.