BIOMEDICAL AND BIOMEDICINE APPLICATIONS OF CNTs - Bio-Inspired and Nanoscale Integrated Computing - page 499

the complexes were tumor specific. SWCNTs have also been used to deliver RNA
interference [49]. A recent study employed short interfering RNA (siRNA), which
is being developed as therapy to inhibit expression of certain genes. Noncovalently
modified SWCNTs with phospholipids were linked through disulfide bonds to
siRNA as well as DNA. Upon endocytosis of the SWCNT complexes, the
disulfide bonds were cleaved by natural cellular mechanisms and the delivered
cargo was able to take effect. This group also covalently attached proteins to
SWCNTs through end and defect oxidized modification and conducted a detailed
study of the internalization mechanism of SWCNTs, concluding that it occurs
through an endocytosis process. In addition, the group showed that noncovalent
absorption of proteins onto end and defect oxidized SWCNTs serves as a general
intracellular protein transporter for proteins 80 kDa [50].

Another unique means of CNT-based gene delivery was achieved through
''nanotube spearing'' where as-grown CNTs with carbon encapsulated nickel
(catalyst) particles remaining at their tips were used to magnetically drive plasmid
DNA modified CNTs into cells. The group succeeded in transfecting cells that had
only previously been transfected with viral vectors [51].

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18.4.2. Hyperthermia Therapy
In addition to delivering therapeutics, carbon nanotubes are a prime candidate for
hyperthermia therapy. Hyperthermia therapy is the use of heat to damage or kill
cancer cells. SWCNTs have been shown to absorb NIR radiation and generate
heat while tissue is transparent in this region. This property has been exploited
through noncovalent functionalization of SWCNTs with oligo nucleotides and
phospholipids containing folic acid that targets folate receptors on cancer cells,
thereby targeting the SWCNT complex to these cells. Researchers have shown
that the SWCNT complexes selectively target the folate receptor containing cells
and are internalized, while cells without these receptors are avoided [52].
Irradiation of the tissue with an 808 nm laser (GaAs) causes the SWCNTs to
heat up. The SWCNT complexes, which remain in endosomes after cellular
uptake, are released upon pulsed radiation by the laser source, allowing the
complexes to enter the cell nucleus. Prolonged irradiation generates enough heat
to destroy the targeted cells while the cells without internalized SWCNTs are
unharmed.

18.4.3. Biomedical Imaging
In addition to their potential as therapeutics or delivery vehicles for therapeutics,
nanotubes might also be used for imaging purposes. New imaging capabilities
based on nanotubes could be harnessed in biomedical research, clinical diagnosis,
and new multifunctional therapeutics. It is likely that future therapeutics will not
only have the capabilities to target specific tissues or cell, but they will also have
imaging agents that will enable clinicians to ensure that the therapeutics have hit
their targets. Because nanotubes have unique optical properties and can be linked