Biomedical Engineering Reference
In-Depth Information
that avoidance of breaks in continuous 14 bp segments of the nanostructure can
dramatically enhance folding. This result suggests that the corresponding 14 nt
segments of the staple strands act as “seeds” that can nucleate proper folding of
the desired target structure. Another effort made by them was towards improving the
purification of DNA origami [
29
]. Based on a modified DNA electroelution method,
they greatly increased the recovery yield of intact DNA origami from agarose gel to
71
˙
3% which is much higher than that of 15
˙
5% gotten from the pellet-pestle
homogenization method (Fig.
10.3
c).
Generally, AFM is the most powerful tool for the characterization of DNA
origami. Agarose gels, stained TEM, and cryo-TEM are also used in some cases
[
30
]. However, for most nanomaterials, normal TEM (unstained TEM) is more
commonly used. In a report published by Jeon and Lee et al., they showed their
efforts in direct imaging and chemical analysis of DNA origami with conventional
TEM [
31
]. They explained that the reason why carbon-composed substrates are
not suitable for DNA origami imaging could almost certainly be ascribed to their
hydrophobic nature. Instead, extremely thin amorphous silicon membranes offer
greater opportunities. Firstly, this substrate shows a suitable hydrophobicity for
DNA origami absorption. Secondly, the absence of carbon in the substrate is
beneficial to the structural and chemical analysis, for example, elemental mapping
with EFTEM technique. Their study also showed the high durability of DNA
origami under 200-kV electron beam exposure.
Since DNA origami is regarded as a new type of nanomaterials, researchers
are also highly concerned about its physical, chemical, and biological properties.
Kuzyk et al. developed a dielectrophoresis-based method for trapping DNA origami
structures between nanoelectrodes and controlled positioning of origami structures
on a chip [
32
]. The method provides a means of bridging bottom-up self-assembled
DNA origami and top-down fabrication approaches. Subsequently, they measured
the conductivity, and experimentally analyzed the conductivity mechanisms, of
single rectangular DNA origamis trapped and immobilized between nanoelectrodes
by utilizing alternating-current impedance spectroscopy [
33
]. The experiments
showed that the nature of the DNA origami conductivity is not purely ohmic
but that it is a combination of ionic diffusion and electronic conductivity, with a
resistance of
for a
90-nm-long DNA origami. Bellido et al. studied
the temperature dependences of the current-voltage characteristics of a sample of
triangular DNA origami deposited in a 100-nm gap between platinum electrodes,
and they suggested a hopping conduction mechanism in the range 280-320 K [
34
].
The same group also measured the frequency response of triangular DNA origami
at room temperature [
35
].
Dong and Besenbacher et al. carried out an in situ thermally controlled AFM
study to reveal the melting behavior of DNA origami on surface (Fig.
10.3
d) [
36
].
Furthermore, by careful control of the temperature cycling, the reversible self-
assembly process of a rectangular DNA origami tile could be directly visualized.
Based on the experimental results and theoretical predictions, they concluded that
the local staples beside the bridged seam contribute significantly to the initial
disassembly. On the other hand, Endo and Sugiyama incorporated photosensitive
70 M
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