Biomedical Engineering Reference
In-Depth Information
As regards nanoelectrode platform for biosensor development, a vertically
aligned CNT array was fabricated by Nguyen's group at the NASA research
centre.
83
In this study, the initial treatment in strong acidic conditions, aimed to
remove the metal catalyst and introduce carboxylated functions at the opened
ends of CNTs, was found to be detrimental for both stability and alignment
of the tubes. In order to overcome such limitation, a spin-on glass (SOG) ilm
was deposited between individual CNTs (Fig. 5.24). Pre-treatment with SOG
provided structural support to CNTs, retaining their vertical coniguration
during the subsequent oxidising treatment. The -COOH groups at the tips
of CNTs were then activated through (3-dimethylaminopropyl) carbodiimide
hydrochloride (EDC), forming a highly reactive
o
-acylisourea active
intermediate, which, in the presence of excess of
N
-hydroxysulfo-succinimide
(sulfo-NHS), gave a more water-stable sulfosuccinimidyl derivative. Finally,
the intermediate underwent a nucleophilic attack by the free amino group
of a luorescence-labelled oligonucleotide, originating the inal peptide
bond.
84
It is worth mentioning that conjugation of nucleic acid did not occur
on the SOG surface in the absence of CNTs, thus conirming the speciicity
of the interaction and the improved chemical coupling of nucleic acids. Two
main advantages are associated with this study: First, the array was made
up of CNTs with uniform length, and thus it overcame the inhomogeneous
distribution usually encountered with suspended tubes. Second, the addition
of SOG rendered the CNTs' interface hydrophilic and thus more suitable for
coupling chemistry in aqueous media.
O
O
HO
OH
O
OH
OH
O
1) SOG
2) 430 C, air, 1 h
3) H
2
SO
4
/HNO
3
33
34
NH-DNA
O
AND-HN
O
O
NH-DNA
NH-DNA
1) EDC, Sulfo NHS
2) H
2
N-DNA
O
35
Figure 5.24
Fabrication and pre-treatment of carbon nanoelectrode arrays with SOG
for functionalisation with DNA.
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