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.
Merging of bridging staples with adjacent oligonucleotide sequences leads to a moderate increase of DNA origami stability, while enzymatic ligation after assembly yields a reinforced nanostructure with superior stability at up to 37 °C and in the presence of 6 M urea.
Earth-abundant catalysts based on transition metal phosphides (TMPs) such as CoxP have recently gained a lot of attention in the field of electrocatalysis and are usually acquired by chemical synthesis.
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