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 134

bioactive molecules and to selectively kill cancer cells. More precisely,
upon exposure of HeLa cells to CNT-DNA solution at 37°C, the SWCNT-DNA
conjugates were internalised inside the cytoplasm but not inside the nucleus
of cells. On the contrary, when the same experiment was conducted at 4°C,
no cellular uptake was observed, thus suggesting endocytosis as the main
mechanism involved. However, after NIR radiation (six 10 s on-and-off pulses
of 1.4 W/cm 2 laser radiation) confocal imaging revealed co-localisation of
luorescent DNA in the cell nucleus (Fig. 5.28), indicating successful release
of DNA from SWCNTs and nuclear translocation after the laser pulses.

(a)

(b)

Figure 5.28 Confocal image of in vitro HeLa cells after a 12 h incubation in a
luorescent-DNA-SWCNT solution. (a) Dual detection of luorescent-DNA-SWCNTs
(green) internalised into a HeLa cell with the nucleus stained by DRAQ5 (red). (b)
Co-localisation (yellow) of luorescent DNA (green) in cell nucleus (red), after NIR
irradiation of 2.5-5 mg/L of SWCNT-DNA, indicating translocation of DNA to the
nucleus. Reproduced from Kam et al. 92 with ]permission. See also Colour Insert.

In order to test whether NIR irradiation was toxic to normal cells, a
control experiment was performed on cells under 808 nm laser radiation
at 3.5 W/cm 2 power but without exposure to SWCNTs: all cells survived,
conirming high transparency of biosystems to NIR light. Conversely, for cells
incubated with SWCNTs, extensive cell death was observed after 2 min of
radiation under a power of 1.4 W/cm 2 . In fact extensive local heating of CNTs
inside living cells, caused by continuous NIR absorption, was the most likely
origin of cell death. Notably, dead cells ''released'' SWCNTs to form black
aggregates loating in the cell medium solution visible to the naked eye 24
h after irradiation. On the whole, selective NIR radiation triggered cell death
without harming normal cells.
The same principle was adopted in the investigation by Gmeiner et al. , 95
who used MWCNTs for selective thermal ablation of malignant cells. DNA-
encased MWCNTs conferred aqueous solubility to the tubes and produced