BIOMEDICAL APPLICATIONS IV: CARBON NANOTUBE-NUCLEIC ACID COMPLEXES FOR BIOSENSORS, GENE DELIVERY AND SELECTIVE CANCER THERAPY - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 129

As an alternative to the immobilisation of CNTs and their subsequent
chemical ligation to DNA, Woolley suggested a different approach, consisting
of alignment of dsDNA on a Si substrate and a subsequent treatment with
a bifunctional bridging compound (1-pyrenemethylamine hydrochloride
[PMA]) and a inal incubation with acid-puriied SWCNTs. 85 The amine group
in PMA was expected to interact electrostatically with the negatively charged
phosphate backbone of DNA, while the aromatic pyrenyl group was reported
to interact strongly with the surfaces of SWCNTs through π-stacking forces. 86
Although this work presented the potential to facilitate the construction of
ordered arrays, it also showed the limitation of ∼ 5% of the total DNA length
covered with speciically aligned SWCNTs and about 60% of all SWCNTs
deposited on DNA fragments, thus suggesting that the methodology still
needs to be optimised.

5.4 CNTNUCLEIC ACID COMPLEXES FOR GENE DELIVERY AND
SELECTIVE CANCER TREATMENT

5.4.1 CNT-DNA complexes for gene therapy

CNT-DNA complexes might become useful tool for gene delivery, provided (i)
DNA is condensed by the nanotube, (ii) it is transported inside the cell where
it should be delivered and inally (iii) it enters the nucleus prior to transgene
expression. Therefore, it is imperative to evaluate the physicochemical
properties of the complexes in order to achieve the best results. The formation
of such complexes between positive and negative charges was the basis of
the experiments performed by Pantarotto et al. , who investigated the effect
of three cationic nanotubes (Fig. 5.25) on gene expression 87 : in particular,
SWCNTs as mono- (SWCNT-NH 3 + , compound 36 ) or bis-adducts (SWCNT-Lys-
NH 3 + , compound 37 ) and cationic MWCNTs (MWCNT- NH 3 + , compound 38 )

NH 3 + Cl -

O

-Cl+H 3 N

O

NH 3 + Cl -

O O

N

N N

O

NH 3 + Cl - N O

O

36

36

37

37

38

38

Figure 5.25. Structure of cationic CNTs: SWCNT-NH 3 + ( 36 ); SWCNT-Lys-NH 3 + ( 37 );
MWCNT-NH 3 + ( 38 ).