BIOMEDICAL APPLICATIONS VI: CARBON NANOTUBES AS BIOSENSING AND BIO-INTERFACIAL MATERIALS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 200

methods to detect the bio-distribution of the SWNTs. Clear NIR luorescence
was detected from tissue specimen slices. This provides a powerful tool to
speed up the development of related medical applications.

7.2.3.2 Raman spectrum

Besides luorescence, CNTs also give out Raman spectra. 50 CNTs often produce
three typical strong Raman bands. The irst band can be found within 150-
300 cm -1 . It is caused by uniaxial vibrations and is called radial breathing
mode (RBM). The second band locates at 1590-1600 cm -1 and is named
tangential mode (or G band). The last one is called the disorder mode (D
band, at 1250-1450 cm -1 ) and is observed in all sp 2 -hybridised disordered
carbon materials . Both metallic and semiconducting SWNTs demonstrate
intense Raman scattering. 58,59 Heller et al. 53 encapsulated SWNTs by DNA
oligonucleotide. The dispersed SWNTs not only emitted luorescence spectra
but were also accessible for detection via Raman scattering in live cells.
Raman scattering of CNTs in murine 3T3 cells and murine myoblast stem
cells remained constant during continuous excitation, suggesting that CNTs
may provide another feasible method for biological sensing and analysis.

7.2.3.3 Electric luminescence

Polarised infrared optical emission can be electrically induced from CNTs. 60
This was achieved on a CNT-based transistor by drawing electrons into the
channel at the source and by producing holes into the channel at the drain.
The mechanism of the IR emission is the radiative recombination of injected
electrons and holes. Such an IR source may form the basis for ultra-small
integrated photonic devices. It provides a possible light source for responsive
sensors and analysis. Freitag and coworkers 61 studied the factors inluencing
the electric luminescence of CNTs and indicated that the environment defects,
such as local dielectric changes, nanotube-nanotube contacts in looped tubes
as well as nanotube segments close to the electronic contacts may change the
electric luminescence. These results suggested that the electric luminescence
is susceptible to environmental changes.

7.2.3.4 Fluorescence quenching

The luorescence of CNTs can be strongly suppressed by speciic chemicals,
and sometimes such quench is reversible. Hence the change of the
luorescence may provide information for the sensing and analysis of the
chemical environment.