BIOMEDICAL APPLICATIONS VI: CARBON NANOTUBES AS BIOSENSING AND BIO-INTERFACIAL MATERIALS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 197

(13, 2) 1307 859 211.9

(9, 7) 1323 790 214.9 215

(12, 4) 1342 857 207.5

(11, 4) 1372 714 221.5

(12, 2) 1376 685 227.0

(10, 6) 1380 756 213.4

(11, 6) 1397 858 200.8

(9, 8) 1414 809 203.4

(15, 1) 1425 927 193.6

(10, 8) 1474 868 192.5

(13, 5) 1485 928 187.2

(12, 5) 1496 795 198.3

(13, 3) 1497 760 203.4

(10, 9) 1555 892 183.3

223.5

* Using __ v RBM =

_________

d t (nm) + 12.5 and assuming a C-C bond distance of 0.144 nm.
As shown in Table 7.1 , most CNTs have their luorescence emission
wavelength in the near-infrared range (800-1600 nm). 48 Actually, the near-
infrared (NIR) spectrum of CNTs has attracted a lot interest for bioanalysis,
because this wavelength range is a special spectral window, which is
transparent to biological systems. Kam et al. 49 reported solubilising CNTs in
the aqueous phase by non-covalently adsorbing either 15-mer luorescently
Cy3-labelled ssDNA or polyethylene (PEG)-grafted phospholipids (PLs).
The molar extinction coeficient of the solubilised SWNTs (length ~150 nm,
diameter ~1.2 nm) measured at λ = 808 nm in the NIR was ε = 7.9 × 10 6
M -1 cm -1 . Therefore the light at this wavelength transferred energy to CNTs
without disrupting the cells.
Meanwhile, the NIR luorescence emission of CNTs has strong advantages
over visible luorescence for biological sensing and analysis. First, there is low
noise from biological tissues and cells at this wavelength range. The blood
and tissues often give light interference with the NIR from the dispersed
CNTs. Second, the dispersed CNTs have a relatively high quantum yield of
luorescence, which was hinted by the high signal-to-noise ratio. 50 The quantum
yield of luorescence for semiconducting CNTs was initially estimated at 0.1
%. 47 It was believed that such low quantum yield of luorescence was caused
by the ensemble of tubes into bundles, since suspended SWNTs in density
gradient fractions showed a quantum yield not less than 1%. 51 Carlson 52
dispersed CNTs with sodium cholate in D 2 O and measured the luorescence
from SWNTs by epiluorescence microscopy on an inverted microscope. The
luorescence intensities from individual SWNTs showed the average quantum
yield value of 3±1%, which is two orders greater than the value of CNTs in