BIOMEDICAL APPLICATIONS VI: CARBON NANOTUBES AS BIOSENSING AND BIO-INTERFACIAL MATERIALS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 191

reported the study of developing highly speciic electronic biomolecule
detectors for proteins using CNTs as a platform. Nanotubes can be directly
used as an electronic analytical tool to detect and monitor protein adsorption
with high sensitivity. In Fig. 7.4a is shown a typical of such electronic devices,
in which a semiconductive CNT-based transistor plays a crucial role. As the
transistor could respond to non-speciic bonded protein, some polymers, such
as Tween 20, were used to cover the CNTs for protein resistance, while speciic
binding with proteins was re-enabled by covalent bonding to the polyethylene
oxide (PEO)-functionalised nanotubes. Applications of such sensors included
the detection of streptavidin (SA) (where biotin was conjugated on the
tween terminal by 1,1-carbonyldiimidazole-mediated nucleophilic addition
(Fig. 7.4b), the detection of IgG (with staphylococcal protein A [SpA])
conjugated (Fig. 7.4c) and the detection the mAbs (with human autoantigen
immobilised [Fig. 7.4d]). Binding of the functional molecules resulted in an
electric response in the CNTs and made the direct electronic readout possible,
providing a more convenient technique in comparison with the traditional
protein labelling method.
Star et al. 31 prepared a nano-FET for detection of proteins. The non-
speciic binding between CNTs and proteins was eliminated by polymer
wrapped on CNTs. The biotin conjugated on the polymer could bind with
streptavidin. The conductance, as well as the gate voltage of the nano-FET,
changed signiicantly upon exposure to streptavidin.
Because of the ability to detect proteins as described above, CNTs were used
for some medical purposes, such as cancer diagnosis. Li 32 used a CNT-based
transistor to detect prostate-speciic antigen (PSA), which is an oncological
marker for prostate cancer. PSA monoclonal antibodies linked with CNTs
were used to anchor PSA. The conductance and gate voltage of the transistor
responded to PSA sensitively and speciically. Therefore it is plausible that
more novel therapeutic and diagnostic devices will be developed using CNTs
in future.
7.2.2.2.3 Structure sensor
The helix structure of CNTs might recognise special chemical molecules.
Ju 33 reported the selective assemble of chiral CNTs with other compounds:
for example, the lavin mononucleotide wrapping around speciic
SWNTs in a helical pattern. The selection was due to the structure of the
assembled molecules. The chiral CNT has the helix structure, while the
lavin mononucleotide consists of an aromatic isoalloxazine moiety and
a chiral -ribityl phosphate group. The isoalloxazine moiety of the lavin
mononucleotide may form pi-pi interactions with SWNTs, and the uracil