DNA Origami Nanostructures - DNA Nanotechnology: From Structure to Function - page 205

Following this design principle, a series of 2D and 3D DNA nanostructures with
high curvature, such as concentric rings, spherical shells, ellipsoidal shells, and a
nanoflask, were assembled successfully. This strategy improves the ability to control
the intricate structure of DNA nano-architectures and create more diverse building
blocks for molecular engineering.
Tensegrity, or tensional integrity, is a property of a structure indicating a reliance
on a balance between components that are either in pure compression or pure tension
for stability. In a work inspired from tensegrity structures, Liedl and Shih reported
3D prestressed DNA origami analogues (Fig. 10.2 g) [ 24 ]. The main body of the
structure is built with rigid bundles of DNA double helices, and several single-
stranded DNA scaffold segments act as tension-bearing cables. The DNA tensegrity
structures can self-assemble against forces up to 14 pN, which is twice the stall force
of powerful molecular motors such as kinesin or myosin.

10.4 Concerns on Assembly Strategies, Characterizations,

and Properties

While building new complex DNA origami structures is the prominent goal in
the field, efforts towards optimizing and developing assembly methods have also
gained more and more attentions. Distinct from the conventional annealing methods,
Simmel's group proposed an isothermal assembly technique to realize the formation
of DNA origami nanostructures at a constant temperature (Fig. 10.3 a) [ 25 ]. Based
on the theory that denaturing agent formamide lowers DNA melting temperatures
linearly by approximately 0.6 ı C per % formamide in the buffer, they achieved
the assembly of DNA origami rectangles and six-helix bundles from a mixture of
viral strand and staple strands which was prepared in hybridization buffer at room
temperature containing a large amount of the denaturant formamide, by gradually
reducing the concentration of formamide through either continuously pumping
normal buffer or dialysis-based methods. Inspired from the isothermal method,
Shih's group was succeeded in using one double-stranded DNA as two sets of
scaffolds for preparing two distinct DNA origami shapes in a one-pot reaction
(Fig. 10.3 b) [ 26 ]. While the standard annealing protocol resulted in failure, they
found that after heating the dsDNA scaffolds and short staples in the presence of
40% formamide, the combining of a fast temperature drop and gradual removal of
the chemical denaturant formamide led to the success in making a tubular shape
and a triangular shape in the same solution. This dsDNA strategy will facilitate
the scaling of DNA origami to greater complexity and mass production due to
the relative ease in obtaining double-stranded DNA of greater lengths, diverse
sequences, and mass quantities. In another way for the mass production, Wooley's
group introduced PCR method for the amplification of long scaffold DNA, and
the useless complementary strand to the scaffold could be removed by magnetic
beads [ 27 ].