Biomedical Engineering Reference
In-Depth Information
Moreover, N-doped CNTs have been found to be less toxic than undoped
ones. 66 Experiments have been carried out with nanotubes of different lengths,
obtained after treatments in sulphuric and nitric acid, to assess the inluence
of this parameter on the heating. 65 Cells have been incubated for 24 hours
with CNTs 1,100 nm and 700 nm in length, respectively, with a nanotube-
to-cell ratio of 1,000, and irradiated with an NIR laser at 1,064 nm (3 W/
cm 2 , 4 minutes). An increase in temperature (~20°C) was observed, with the
consequent death of a big percentage of cells (more than 90%). Differently, for
330 nm long nanotubes, no such effects were detected. This is a conirmation
of the antenna theory, according to which nanotubes should be at least as
long as one-half of the incidental radiation to absorb light eficiently. Since
the laser used had a wavelength of 1,064 nm, 330 nm long nanotubes were
not long enough to couple effectively.
Gomez-De Arco et al. covalently functionalised oxidised SWCNTs with a
luorescent probe and demonstrated internalisation of these compounds by
glioblastoma multiforme (GBM) brain tumour cells. 67 The cells were treated
with nanotubes and then imaged by Z-stack luorescence to analyse all their
inner volume, showing an actual intracellular localisation, especially in the
region surrounding the nucleus. The same cells were not able to internalise
the luorescent molecule alone, thus conirming the ability of CNTs to
transport cargos through cellular membranes. Furthermore, cells which
had internalised the nanotubes and, as a control, cells without nanotubes
were exposed to NIR radiation (808 nm, 0.8-1.5 mW/cm 2 , 1-10 minutes).
This treatment resulted in cytotoxicity, due to intracellular hyperthermia
caused by the heating of the nanotubes (cell survival of 10-20%), while the
irradiation in the control samples did not exert any toxicity (cell survival of
95%) thanks to the transparency of the cells to NIR wavelength light.
Photothermal therapy has been also applied to achieve antimicrobial
activity 68 by exploiting the ability of CNTs to bind to bacteria. 69 Two different
kinds of CNT preparations, one with well-dispersed CNTs and the other
containing clusters, have been incubated with bacteria cultures. In both
cases, the absorption of CNTs into bacteria was observed. The samples were
irradiated by multi-pulse lasers at 532 and 1,064 nm, with pulses of 12 ns, at
different laser luences. Local thermal phenomena led to complete bacteria
disintegration at laser luence values of 2-3 J/cm 2 in all cases.
The ability of CNTs to convert optical energy into thermal energy upon
exposure to NIR light was also exploited by Panchapakesan et al ., using a
different approach. 70 A so-called nanobomb was built up using SWCNTs
as agents to kill breast cancer cells. The thermal response of CNTs to NIR
irradiation (800 nm, 50-200 mW/cm 2 , less than 60 seconds) caused
vaporisation of the water trapped in the CNT bundles, thus creating a big
pressure and a consequent explosion, with cancer cell death. Interestingly,
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