Binding-induced internal-displacement of inverted aptamer beacon: Toward a novel electrochemical detection platform

• A universal electrochemical aptasensor fabrication strategy was developed.
• Binding-induced internal-displacement of inverted aptamer beacon
• Signal-on electrochemical aptasensor
• Sensitive detection of thrombin
• The aptasensor is regenerable and reusable.

In this paper, we reported a novel electrochemical aptasensor based on an inverted aptamer beacon (IAB). The IAB architecture with a hairpin structure consisted of an aptamer arm and a ferrocene (Fc)-labeling signal arm, and was inverted on the electrode through a thiol-linker on the middle site of its loop. The inverted immobilization strategy prevented the end-labeling of ferrocene tag from approaching the electrode, thus resulting in a weak electrochemical signal. In the presence of thrombin, binding of target with the aptamer arm displaced the signaling arm, producing a flexible single-stranded element, i.e. internal-displacement which allowed Fc tag to collide with the electrode, thereby producing a relatively strong electrochemical signal. By monitoring the increased signal, thrombin could be readily detected in the signal-on mode with a detection limit (LOD) of 0.21 nM. Inspiringly, the IAB-based strategy required no auxiliary strands and did not depend on structure-switching of specific aptamer/target couple, thus presenting as a generalized method for fabrication of other electrochemical aptasensors.