Four-way junction-driven DNA strand displacement and its application in building majority logic circuit.

We introduced a four-way DNA junction-driven toehold-mediated strand displacement method. Separation of the different functional domains on different strands in the four-way junction structure and usage of glue strand to recombine them for different logic gates make the design more flexible. On the basis of this mechanism, a majority logic circuit fabricated by DNA strands was designed and constructed by assembling three AND gates and one OR gate together. The output strand drew the G-rich segments together to form a split G-quadruplex, which could specifically bind PPIX and enhance its fluorescence. Just like a poll with three voters, the high fluorescence signal would be given off only when two or three voters vote in favor. Upon slight modification, the majority circuit was utilized to select the composite number from 0 to 9 represented by excess-three code. It is a successful attempt to integrate the logic gates into a circuit and to achieve desired functions.