BIOMEDICAL APPLICATIONS I: DELIVERY OF DRUGS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 27

The simplest procedure includes the attachment, by physical adsorption,
of pCNTs to several molecules such as pyrene, naphthalene derivatives, 95
sulfonated polyaniline, 96 poly(acrylic acid), 97 proteins, DNA 98 - 100 and gold
nanoparticles. 101 The nanotube-adsorbate conjugation consists of π - π
stacking interactions between the aromatic part of the adsorbate and the
graphitic sidewall of nanotubes. Therefore, this does not affect CNTs' whole
integrity. An interesting approach is summarised in Scheme 2.3, which on
one side enabled the irreversible adsorption onto the surface of SWCNTs
through π - π interactions, while its additional succinimidyl ester group
allowed the covalent attachment of various molecules via the nucleophilic
attack of primary or secondary amines (such as in ferritin, streptavidin or
biotin-polyethyleneoxyde-amine). 56
Scheme 2.3 Amine groups on a protein react with the anchored succinimidyl ester
to form amide bonds for protein immobilisation. Reproduced from J. Chen et al. 56 with
permission.
The signiicant increase in CNT dispersibilty 59,102 - 105 is another beneicial
effect of this interaction, and it has been utilised for puriications of CNTs
from contaminations represented mainly by amorphous carbon. 106 - 108
With similar methodologies, debundling CNTs may be obtained using
surfactants 56,57,109 - 113 or solubilising polymers. 59,114 Several surfactants
(either anionic, nonionic or cationic) are able not only to suspend CNTs in
aqueous solution, 109 - 112 but also to prevent re-aggregation of the tubes by
Coulomb repulsion between surfactant-coated CNTs. 114 In addition, if the
surfactant presents aromatic groups in its hydrophobic part, additional π - π