Molecular self-assembly has been successful in utilizing Watson-Crick base-pairing to build complex 2D/3D DNA nanostructures in the solution phase. However, integrating with solid substrates for device application in nanoelectronic/nanophotonic circuits has been slowly progressing due to the lack of understanding how molecular assemblies and their components interacting with surfaces. Strong surface attractions are used to immobilize the assemblies for structural characterization but it remains a speculation as to how these interfacial interactions alter self-assembly pathways. Evidences showed that weakening surface attraction enables mobility of adsorbed molecules and partial assemblies, but also exerts repulsive interaction causing desorption from surfaces. Here, we studied the staple-assisted folding of single-stranded DNA (ssDNA) scaffolds (DNA origami) end-tethered to a carboxyl-terminated self-assembled monolayer (SAM), which allowed us to modulate precisely DNA-surface interactions between attractive and repulsive regimes without irreversible desorption. Thiolated DNA anchor strands were inserted into SAM defects and used to capture ssDNA scaffolds, which were then incubated with a saline/formamide buffer solution containing DNA helper strands (staples) to form predesigned DNA origami. Surface attractions are switched on with divalent cations for <i>in situ</i> high-resolution atomic force microscopy imaging. Switching to monovalent cations, repulsive interactions are turned on to initiate DNA folding. Comparison of folded structures from untethered and tethered scaffolds reveals that strong surface attraction inhibits DNA folding, while a weak surface interaction regime enables high-yield DNA folding. Moreover, on-surface self-assembly simplifies purification of folded structures as unbound reactants can be removed by rinsing and facilitates folding from any long double-stranded DNAs. The sequence-specific hybridization between the surface anchor strand and the scaffold was also utilized to prescribe the outcomes of the surface-seeded DNA origami folding in a programmable fashion. Our strategy of self-assembling structures tethered to dynamic surfaces may serve as a general platform for understanding and managing the influences of interfacial interactions on self-assembly of complex structures. Therefore, it is a step toward programmable self-assembly of hierarchical functional surface architectures.

Surface-seeded folding of DNA origami

2019 Fall National Meeting

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