Robust nucleation control via crisscross polymerization of DNA slats

Natural biomolecular assemblies such as actin filaments or microtubules polymerize in a nucleation-limited fashion. The barrier to nucleation arises in part from chelate cooperativity, where stable capture of incoming monomers requires straddling multiple subunits on a filament end. For programmable self-assembly from building blocks such as synthetic DNA, it is likewise desirable to be able to suppress spontaneous nucleation. However, existing approaches that exploit just a low level of cooperativity can limit spontaneous nucleation only for slow growth, near-equilibrium conditions. Here we introduce ultracooperative assembly of ribbons densely woven from single-stranded DNA slats. An inbound "crisscross" slat snakes over and under six or more previously captured slats on a growing ribbon end, forming weak but specific half-duplex interactions with each. We demonstrate growth of crisscross ribbons with distinct widths and twists to lengths representing many thousands of slat additions. Strictly seed-initiated extension is attainable over a broad range of temperatures, divalent-cation concentrations, and free-slat concentrations, without unseeded ribbons arising even after a hundred hours to the limit of agarose-gel detection. We envision that crisscross assembly will be broadly enabling for all-or-nothing formation of microstructures with nanoscale features, algorithmic self-assembly, and signal amplification in diagnostic applications requiring extreme sensitivity.