Biomedical Engineering Reference
In-Depth Information
cationic lipid and neutral lipid in solution, forming lamellar structures in
which DNA chains are inserted between stacked lipid sheets. The Cd
2+
ions
were organized along the DNA chains in the multilamellar structure, and sub-
sequently reacted with H
2
S to form CdS nanorods. In addition, the widths
of the nanorods can be tailored by adjusting the lipid mixture. This tech-
nique may lead to custom-designed crystals with useful electronic, magnetic,
or optical properties.
3
DNA Strand Pairing
From an energetic point of view, the most important contribution to the DNA
double-helical structure is the pairing bases between the two strands. Two
interactions, hydrogen bonding between paired nucleobases and stacking in-
teractions between adjacent nucleobases play important roles in the stability
of the duplexes [40]. Combining the hydrogen bonds and the hydrophobic
stacking interactions, one DNA strand can associate with and recognize other
DNA stands, which leads to the Watson-Crick type right-handed helix. The
specific recognition between complementary stretches of nucleotides makes
it possible to encode instructions for assembly in a predetermined fashion
on the nanometer scale. Besides the nanoscale structures made of DNA only,
nanostructures made of DNA and other components, or mainly of other com-
ponents have been attempted in various ways. The presence of DNA, with its
controllable molecular properties, enables the creation of constructions with
a predictable ordered structure. Moreover, based on an ingenious comple-
mentarily design, various reports demonstrated that the DNA strand stacking
can also drive nanoscale movements.
3.1
DNA Nanostructure
The familiar dsDNA is a linear molecule not suitable for forming complex
motifs. To build complex DNA nanoarchitectures, branched DNA molecules
are needed. Fortunately, this key problem was resolved. By designing appro-
priate DNA sequences, the branched DNA molecules can be produced by the
conventional solid support synthesis.
Generally, two types of the branched DNA molecule are used to gen-
erate complex DNA nanoarchitectures, which are named “junction” and
“crossover”, as illustrated in Fig. 8 [41, 42].
Early works on the artificial DNA architectures mainly used the branched
junction motifs [43, 44]. Such junctions contain three or four arms of ss-
DNA oligomer (Fig. 8 motifs 1 and 2). Figure 9 shows four units of the
branched junction assemble to produce a quadrilateral (motif 5). The outside
