Signal-on and label-free electrochemical detection of amyloid β oligomers based on dual amplification induced hemin/G-quadruplex formation

Abstract We developed a novel dual-amplification strategy for sensitive electrochemical detection of amyloid β oligomers (AβO) based on exonuclease III-assisted DNA recycling and rolling circle amplification (RCA). In this assay, gold electrode was used to immobilize molecular beacon (H2) with a 3′ overhang as recognition probes and perform the dual signal amplification procedure. In the presence of AβO, the AβO binding aptamer (H1) preferred to form AβO/H1 complex, making the region II of H1 hybridized with specifically designed capture H2 to form a double-stranded structure and created a 3′-blunt end for Exo III to initiate the DNA recycling amplification process to cleave numerous H2 probes. Then, the remaining H2 fragments hybridized as primers with the RCA template to initiate the RCA process. Consequently, hemin stacked into the G-quadruplex forming region, and the hemin/G-quadruplex was formed, generating an amplified electrochemical signal by differential pulse voltammetry. This novel signal amplification strategy could detect target AβO down to 39 fmol L−1, with a dynamic range spanning five orders of magnitude. Moreover, the approach is free of any label conjugation step and thus has great potential for the development of robust aptasensors.