Self-Assembled DNA-Inorganic Nanoparticle Structures - DNA Nanotechnology: From Structure to Function - page 186

QD-gold hetero-structures (Fig. 9.3 d) [ 27 ], in which the QDs was surrounded by
different numbers of AuNPs. These heterogeneous nanostructures were assembled
through hybridization of the complementary DNA bound to the particle surface
and further purified by gel electrophoresis. Recently, Kelley et al. [ 28 ]havealso
developed the DNA-directed formation of QD-based nanostructures. QDs bearing
from one to five DNA strand were synthesized and then used as building blocks to
create a variety of rationally designed assemblies, including cross-shaped complexes
composed of three different types of dots (Fig. 9.3 e). This work confirmed that the
energy transfer exists between the QDs with different emission wavelengths, which
will help the construction of nanoscale optoelectronic devices.

9.3.2 DNA Motifs for Self-Assembly

Except for serving as a linker to facilitate the assembly process as mentioned
above, DNA can be also used to form rigid building blocks for the construction
of complex nanostructures. Seeman and coworkers proposed for the first time the
possibility of combining branched DNA with sticky ends to construct 2-D arrays,
which was later experimentally realized by his group [ 29 ]. Further, they constructed
a group of branched complexes called crossover tiles with greater rigidity, such as
double-crossover (DX) tiles [ 30 , 31 ], triple crossover (TX) tiles [ 32 ], and paranemic
crossover (PX) tiles [ 33 , 34 ]. These works opened up a new world in the field of 2-D
assembly of nanomaterials.
Xiao [ 35 ] reported the self-assembly of metallic NP arrays using DNA DX tiles
as a programmable molecular scaffold. They designed four types of DNA DX tiles
and modified a small AuNP, 1.4 nm in diameter, to one of those predesigned DX
tile, and then integrated these four DNA DX tiles into nanoarray through specific
base-pair recognition (Fig. 9.4 a). Kiehl group reported that AuNPs capped with
ssDNA were located into high-density 2-D arrays by a process in which DNA-Au
nanoconjugates were hybridized onto preassembled 2-D DNA tile scaffold. Those
gold prototype nanoelectronic components were programmably self-assembled into
closely packed rows with precisely defined inter-row spacings (Fig. 9.4 b) [ 36 ].
Later, Kiehl and coworkers [ 37 ] continued their efforts to precisely arrange multiple
DNA-encoded nanocomponents into nanoarrays by changing the size of AuNPs
used; the DNA tile scaffold was designed to assemble 5-nm and 10-nm AuNPs
into equally spaced alternating AuNPs rows (Fig. 9.4 c). They developed another
flexible strategy by using two kinds of DNA motif equipped with 5-nm and 10-nm
AuNPs, respectively, to form periodic NP arrangement. Adjusting the combinations
of different motifs could produce versatile dimensional crystalline arrays (Fig. 9.4 d)
[ 38 ]. At the same time, Yan [ 39 , 40 ] group also reported a similar work on
the periodicity and interparticle spacing of the NP nanoarray (Fig. 9.4 e). They
developed a new DNA-NP conjugates that are readily assembled onto a DNA-tiling
system. This novel system is amenable both to the DNA-tiling lattice formation
and the prevention of nonspecific aggregation between the AuNPs, thus has special