ABSTRACT
Toehold-mediated DNA strand displacement has proven powerful in the construction of various DNA circuits, DNA machines, and biosensors. So far, many new toehold activation mechanisms have been developed to achieve programmed DNA strand displacement behaviors. However, almost all those toeholds are inflexible via either a covalently attached manner or a complementary hybridization strategy, which limit the versatility of DNA devices. To solve this problem, we developed a new toehold, named "cooperative toehold", to activate DNA strand displacement. On the basis of a base stacking mechanism, the cooperative toehold is comprised of two moieties with completely independent DNA sequences between each other. The cooperative toehold enabled one to continuously tune the rate of DNA strand displacement, as well as more sophisticated strand displacement reactions. The cooperative toehold has also been employed as a universal signal translator for biosensors to qualitatively determine RNA and ATP. Moreover, as a novel specific PCR monitoring system, cooperative toehold-mediated DNA strand displacement can detect the pUC18 plasmid in genomic DNA samples with an aM detection limit.