Self-Assembled DNA-Inorganic Nanoparticle Structures - DNA Nanotechnology: From Structure to Function - page 187

advantages in well-defined stoichiometry and resistance to high salt concentration
which are difficult to achieve with other methods. Soon, QDs were also positioned
on the 2-D tile template by Yan group [ 41 ]. As the QDs are not so easily modified by
thiol-terminated DNA like AuNPs, so the streptavidin-capped CdSe/ZnS core/shell
QDs were used for specific affinity to biotin periodically anchored on the tile
template. Finally, they constructed well-aligned 2-D arrays of QDs with controlled
periodicity (Fig. 9.4 f), which demonstrates the capability of directing QDs into
designed nanoarchitectures.

9.3.3 DNA Origami for Self-Assembly

For the DNA origami assembly, a long single-stranded DNA strand as a molecular
scaffold and a set of 200 short staple strands bind and make crossovers on the
scaffold, thus folding the scaffold strand into an addressable shape that can display
desired patterns on its surface. DNA origami attains the accuracy of 6-nm resolution
all over the structure. Furthermore, external DNA can be readily hybridized onto
DNA origami structure via complimentary base pairing at specific site; alternatively,
modified DNA can be used as a staple strand for the folding of the scaffold. So DNA
origami as a robust scaffold enables well-ordered organization of a wide range of
NPs whose surface is engineered through DNA modification. In the following years
after the invention of DNA origami, quite a lot of researches on selective positioning
of AuNPs on DNA origami scaffold have been reported.
Sharma et al. [ 42 ] reported a prominent work by using lipoic acid-modified DNA
oligonucleotide to prepare a 1:1 ratio of AuNP-DNA conjugates with a bivalent
thiolate-Au linkage. The AuNP-DNA conjugates were purified using agarose gel
electrophoresis and were passivated by a layer of short oligonucleotides composed
of five thymine residues and modified with a monothiol group in the end. This
passivation enhances the dispersibility of the AuNPs in high salt-containing buffer
solution. Then, the AuNPs-DNA conjugates were assembled onto a rectangular
DNA origami at desired positions. AFM images showed that the yield of the
desired final structures was significantly improved from 45% (monothiol approach)
to 91% (dithiol approach) (Fig. 9.5 a). Ding et al. [ 13 ] adopted an alternative
approach in which different-sized AuNPs individually modified with multiple short
DNA strands were firstly prepared and then mixed with a triangular DNA origami
structure bearing three complementary strands at each predesigned site for AuNPs
selective attachment. Finally, 6 AuNPs of 15-, 10-, and 5-nm diameters were aligned
into a self-similar pattern on a triangular DNA origami scaffold. The structures were
purified and characterized by SEM, showing a high yield in SEM images (Fig. 9.5 b).
Endo et al. [ 43 ] proposed another method to prepare a 2-D DNA origami scaffold
having six long rectangular cavities for placement of AuNPs. In this design, two
dithiolated staples capture one AuNP in the slit cavity. Thus, the slit cavity served
as a guide for the programmed arrangement of the AuNPs (Fig. 9.5 c). A perfect
work that focused on large-area spatially ordered arrays of AuNPs directed by DNA