Biomedical Engineering Reference
In-Depth Information
Ag nanowire positioned between two Au electrodes. A subsequent publica-
tion reported not only making conducting gold and silver nanowires from
DNA templates but also protecting specific regions of DNA molecules from
metal deposition by associating proteins along sections of the DNA [9]. Simi-
lar to these two examples, various metallic nanowires prepared by the de-
position of palladium [10], platinum [11, 12], copper [13] and cobalt [14]
metal on DNA have been investigated as an approach for creating conductive
nanowires.
Not only metal ions, but also positively charged nanoparticles have been
templated onto DNA molecules. Ohtani and coworkers [15] prepared novel
surface-functionalized AuNPs based on the conventional reduction of HAuCl
4
using aniline as a reducing agent. In their work, the AuNPs were successful as-
sembled on DNA molecules by two different procedures. One was assembly
of AuNPs on DNA that was previously aligned on the substrates. The other
procedure first involved binding the AuNPs onto DNA and then subsequent
stretching and fixation of the composite.
2.2
DNA and Collagen
The complex of DNA and collagen has potential uses for fabrication of new
nanostructures. Collagen is the most important structural protein in the
body. It acts as the “scaffolding” of the extracellular matrix and gives skin,
tendon, cartilage, and intervertebral discs their mechanical strength. A colla-
gen molecule consists of three polypeptide chains arranged in a parallel triple
helix. These chains are unusually rich in glycine, proline, and hydroxypro-
line. They are held together by hydrogen bonds that link the peptide amine
bonds of glycine residues to peptide carbonyl groups in an adjacent polypep-
tide. This results in a rigid rod-like triple helix geometry with a diameter of
1.5 nm and a length of about 300 nm for a single collagen molecule. Moreover,
it was reported that there are locations of charged residues in the collagen
structures [16]. As mentioned previously, the dsDNA molecule shows local
stiffness in a range of about 100 nm but long-range flexibility of the double
helix. Exploring the interaction between the two helical biopolymers is useful
for building regular structures at the nanoscale.
The first morphological investigation about complex of dsDNA and colla-
gen was carried out by TEM, and published in 1997 [17]. It was found that the
pattern of the collagen fibrils formed in the presence of DNA was extremely
regular compared with pepsin-digested collagen alone. In addition, the width
of the fibrils was larger than that of the fibrils without DNA (Fig. 5a,b). This
phenomena was confirmed again in a following publication [18]. The re-
sults showed that the presence of linear dsDNA molecules strongly promotes
the fibril's formation, but the circular closed supercoil DNA molecules de-
celerate the complex formation. The phosphate groups of DNA are likely to
