Biomedical Engineering Reference
In-Depth Information
by atomic force microscopy (AFM), although the potential application of such
multifunctional material was not clearly stated. In that case DNA was covalently
bound to previously oxidised CNTs, and a similar procedure was adopted by
another group for the incorporation of an uncharged DNA analogue, called
peptide nucleic acid (PNA) (Fig. 5.8). 30 The use of such neutral sequence,
besides maintaining the hybridisation properties of ssDNA, offers additional
advantages, including resistance of PNA-cDNA complexes towards enzymatic
degradation and improved thermal stability in comparison with ssDNA-cDNA
complexes, because of absence of electrostatic repulsions. And yet, methods
that can characterise the interaction with CNTs, especially in solution, are
still lacking. That is why linear dichroism, recently applied on SWCNT-PNA
complexes solubilised in sodium dodecyl sulfate, 31 seems particularly useful
in demonstrating that the nucleic acid bases lie lat on the nanotube surface
with the backbone wrapping around the nanotube at an oblique angle in
the region of 45 ° . Although the analysis is still qualitative, it was able to
discriminate between the signals provided by the single-stranded PNA and
the larger ones obtained with sonicated double-helix DNA. 32 The authors
suggested that the difference might be due to additional small interactions
coupled with the intrinsically greater rigidity of the duplex DNA (dsDNA).
O
ssDNA
c DNA
H
N
gold particle
CNTs
2
O
1
DNA hybridization
O
O
N
H
NH
HN
HN
O
3
O
O
N
H
O
O
HN
NH
O
O
HN
NH
O
4
O
HN
O
Figure 5.7 DNA-directed self-assembling of multiple carbon nanotubes and
nanoparticles.
 
 
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