Dynamics of DNA Origami Lattice Formation at Solid-Liquid Interfaces

The self-organized formation of regular patterns is not only a fascinating topic encountered in a multitude of natural and artificial systems, but also presents a versatile and powerful route toward large-scale nanostructure assembly and materials synthesis. The hierarchical, interface-assisted assembly of DNA origami nanostructures into regular, 2D lattices represents a particularly promising example, as the resulting lattices may exhibit an astonishing degree of order and can be further utilized as masks in molecular lithography. Here, we thus investigate the development of order in such 2D DNA origami lattices assembled on mica surfaces by employing in situ high-speed atomic force microscopy imaging. DNA origami lattice formation is found to resemble thin-film growth in several aspects. In particular, the Na+/Mg2+ ratio controls DNA origami adsorption, surface diffusion, and desorption, and is thus equivalent in its effects to substrate temperature which controls adatom dynamics in thin-film deposition. Consequently, we observe a pronounced dependence of lattice order on Na+ concentration. At low Na+ concentrations, lattice formation resembles random deposition and results in unordered monolayers, whereas very high Na+ concentrations are accompanied by rapid diffusion and especially DNA origami desorption, which prevent lattice formation. At intermediate Na+ concentrations, highly ordered DNA origami lattices are obtained that display an intricate symmetry, stemming from the complex shape of the employed Rothemund triangle. Nevertheless, even under such optimized conditions, the lattices display a considerable number of defects, including grain boundaries, point and line defects, and screw-like dislocations. By monitoring the dynamics of selected lattice defects, we identify mechanisms that limit the obtainable degree of lattice order. Possible routes toward further increasing lattice order by postassembly annealing are discussed.