Biomedical Engineering Reference
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energy can be transferred into an electric signal in CNTs for convenient
detection, and on the contrary, an electric current can produce light emission
and make CNTs a possible light source for sensing.
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On the other hand, the
quenching of CNTs' luorescence can be used as a tool for the detection of
target materials.
7.2.3.1 Fluorescenceemier
The development of an ultrasonic dispersion method to wrap surfactants
around nanotubes, thereby isolating them, is the major milestone in the
optical characterisation of SWNTs. O'Connell and coworkers
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reported a
study in which they sonicated CNTs with long chain molecules and sodium
dodecyl sulphate (SDS) in aqueous solution to disperse the CNTs and obtain
single CNT suspension. The SDS could form micelles with individual CNTs
as the cores. This method has profound meaning for understanding CNTs'
luorescence properties because these individual CNTs, differently from the
CNTs encapsulated in bundles, were not subjected to perturbation by the
surrounding tubes and showed much better resolved optical absorption
spectra. Furthermore, because some long chain molecules can selectively
wrap speciic CNTs, it is possible to study their spectra separately.
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For
example, in a suspension of CNTs, only SWNTs (7, 5) were wrapped by
poly(9,9-dioctyluoreny1-2,7-diyl) (PFO) and gave out luorescence at a
correlated wavelength (Fig. 7.7). These dispersed CNTs represent potential
luorescence materials for biomarking and bioanalysis.
Figure 7.7
Poly(9,9-dioctyluoreny1-2,7-diyl)-wrapped CNTs (7,5) showed
luorescence emission. Reproduced from Chen
et al.
47
.with permission. See also
Colour Insert.
A detailed study on the CNTs' optical spectroscopy showed that the
luorescence is size-tunable and in close relation with the CNTs' atom
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