Biomedical Engineering Reference
In-Depth Information
and thymine, while in RNA thymine is replaced by the uracil residue. The
structure of the DNA consists of two molecular chains, in which one chain is
tightly bound to the other to form a double helix and they are held together by
many hydrogen bonds. Further, DNA is classiied as a natural polymer, and it
has shown interesting solubilising properties of numerous materials as well
as high sensitivity towards complementary sequences. On the other hand,
a wide variety of applications of matrices made of CNTs for the detection of
bio-organic and inorganic compounds has also been reported.
8-11
One of the irst articles describing the interaction between CNTs and
DNA was published in 2003 by Zheng
et al.
12
: it demonstrated that nucleic
acids could easily adhere to the surface of CNTs on the basis of a
π
-stacking
interaction that dispersed the bundles into individual tubes, while exposing
the sugar-phosphate groups to water. This was conirmed by electronic
adsorption and near-infrared (NIR) luorescence. In a few simulation studies,
the authors also indicated that there were many permissible ways in which
short single-stranded DNA (ssDNA) could bind to the nanotube surface. These
included helical wrapping or simply surface adsorption of a linearly extended
structure, with poly-thymine (poly(T)) showing the highest dispersion
eficiency (Fig. 5.1). It was suggested that both DNA chain lexibility and
backbone charge might have contributed to such high dispersion eficiency.
Very recently, it was even shown that experimental binding energies of
nucleobases with single-walled carbon nanotubes (SWCNTs) in aqueous
solution decrease in the order G > T > A > C.
13
a)
O
O
O
O
O
NH
HN
NH
O
O
HN
NH
O
N
O
N
O
O
N
O
O
NH
HN
O
N
O
O
O
N
O
O
NH
N
O
O
O
H
H
H
H
O
N
HN
O
O
H
H
H
H
H
H
O
H
O
H
H
H
O
O
HO
H
N
O
N
O
HN
O
O
NH
O
H
H
H
O
O
-O
H
H
P
O
O
O
H
P
H
O -
H
O
O
NH
O
H
H
H
H
H
O
HN
N
O
N
O
O
O
-
O
-
H
H
O
H
H
H
O
O
- O
P
O
O
P
O -
HN
NH
O
O
H
-O
H
P
O
O
H
O
P
O -
H
O
H
H
O
N
O
N
O
O
O
O-
O -
H
H
H
H
HN
NH
O
-
O
-
O
O
N
O
N
O
O
O
-O
P
O
O
P
O-
H
H
O
NH
H
H
O
H
H
O
H
H
H
H
HN
O
-
O
N
O
O
N
O
O-
H
H
NH
-
O
H
O
-
H
HN
N
O
O
O
H
P
O
O
O
P
O
H
H
H
H
H
O
N
O
O
-
O
-
O
O
-
O
O
-
H
H
H
H
O
N
O
O
O
P
O
O
P
H
H
O
H
O
H
H
H
O
O
N
HN
O
NH
H
H
H
H
O
-
O
-
H
-
O
H
H
O
-
H
O
H
P
O
O
O
P
O
H
H
O
H
HN
NH
H
H
O
N
N
O
O
-
O
-
H
H
O
H
O
H
H
H
- O
P
O
O
P
O -
O
H
-
O
H
H
O
-
H
O
O
H
P
O
O
O
P
O
H
O
N
N
O
O
O-
O-
H
H
H
H
O
O
-
O
-
O
-O
P
O
O
P
O-
H
O
H
H
O
H
H
H
O
H
O
H
H
H
NH
O
NH
O
N
O
O
O
-
O
-
HN
H
-
O
H
H
H
P
O
O
P
O-
O
H
O
O
H
N
O
O
-
O
N
H
H
H
H
-
O
O
O
-
P
O
O
P
O
O
-
O
O
H
H
O
H
H
O
H
H
O
H
H
H
H
- O
P
O
O
P
O -
H
H
H
H
O
O
O
-
O
-
-O
P
O
O
P
O-
O
-
O
-
-
O
O
O
-
-
O
H
H
P
O
-O
O -
H
O
O-
O
-
O-
-O
H
P
O
H
O
O
H
O
-O
H
P
H
H
P O
O
O
H
H
P
O
-
O
N
P
O
H
H
O
-O
H
O
H
H
HN
O
O
H
H
O
H
O
H
H
O
H
O
H
H
N
O
H
H
O
H
H
N
H
H
O
O
NH
N
O
H
P
O
O
-
NH
-
O
N
N
H
O
H
O
O
N
H
O
O
O
H
O
O
-
HN
O
HN
O
O
O
H
P
O-
H
N
O
H
O
O
N
O
b)
HN
O
H
H
O
H
H
H
N
O
H
N
-
O
H
O
-
O
P
O
O
H
O
H
O
N
H
O
O
H
O
N
O
H
H
O
N
-O
P
O
NH
O
H
H
O
-
N
H
O
H
O
O
O
-
H
O
N
H
N
H
P
O
O
-
H
H
O
H
O
H
H
O
O
- O
O
H
O
H
H
-
O
N
O
P
O
-
P
H
HN
O
O
H
N
-O
O
H
O
H
O
H
P
O
O
H
H
O
O
H
H
-
O
N
N
O
O
O -
NH
H
O
H
O
O
H
O
H
P
O
O-
H
O
O
HN
NH
P
O
H
N
O
O
O
H
O
O
-
O
N
O
N
O
-
O
O
O
O
HN
H
HN
O
NH
H
H
H
H
H
O
H
H
H
PO
O
-
H
H
O
H
O
O
H
O
N
HN
N
-
O
O
-
O
O
P
O
-
H
H
O
N
O
O
H
H
H
H
O
H
PO
O
-
O
H
H
H
H
H
O
-O
H
O
H
PO
O
-
O -
P
O
-O
O -
Figure 5.1
Binding model of a carbon nanotube wrapped by a poly(T) sequence. (a)
The bases (red) orient to stack with the surface of the nanotube and extend away from
the sugar-phosphate backbone (yellow). (b) The DNA wraps to provide a tube within
which the carbon nanotube can reside, thus converting it into a water-soluble object.
See also Colour Insert.
Search WWH ::
Custom Search