Tetrahedral DNA nanostructure-based ratiometric electrochemical aptasensor for fumonisin B1: A unity of opposites in binding site and steric hindrance of large-sized DNA for signal amplification

Large-sized DNA structures have been extensively explored in electrochemical sensing for abundant binding sites or large steric hindrance, yet large steric hindrance could hinder electron transfer of probes on DNA, depressing their efficiency for signal amplification. Herein, a ratiometric electrochemical aptasensor was designed to take advantage of abundant binding sites and large steric hindrance of the tetrahedral DNA nanostructure (TDN) for efficient signal amplification. The working principle is that the recognition of the target leads to a decrease in binding sites and a reduction in steric hindrance, which in turn leads to the opposite change in the two signals. Ferrocene (Fc)-labeled complementary DNA acted as a substrate, while a TDN containing aptamer was used for fumonisin B1 (FB1) recognition and methylene blue (MB) absorption. The binding of FB1 triggered the stripping of TDN, leading to a decreased current of MB (IMB) and an increased current of Fc (IFc). In this way, TDN allowed the enlarged variations in IFc and IMB by the significant change in steric hindrance and binding sites in ratiometric electrochemical sensing, respectively. Consequently, the developed aptasensor offered a linear range of 0.1-100 pg mL- 1 and a detection limit of 0.087 pg mL- 1 for FB1. This strategy offers a new way to fabricate highperformance sensors with large DNA structures.