A simple assay to amplify the electrochemical signal by the aptamer based biosensor modified with CdS hollow nanospheres

A simple method to amplify the electrochemical signal by an aptamer with 22 bases modified with CdS hollow nanospheres (CdSHNs) was described. Using the thrombin as a model, the interaction between the aptamer and CdSHNs was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and circular dichroism spectroscopy. CdSHNs promoted the electron transfer between the gold electrode and K3[Fe(CN)6] and facilitated the conformation conversion of the aptamer from hairpin to G-quadruplex after the aptamer interacted with thrombin. Under optimal conditions, the modified electrode could be used for the determination of thrombin from 0 to 33 μg mL−1 and the sensitivity was 1.34 μA mL μg−1 cm−2, while the linear range of the modified electrode without the immobilization of CdSHNs was from 2.75 to 27.5 μg mL−1 and the sensitivity was 0.062 μA mL μg−1 cm−2. This constructed biosensor also had a good stability, specificity, reproducibility and accuracy which could provide a promising platform for fabrication of aptamer based biosensors.