Biomedical Engineering Reference
In-Depth Information
tissues [60], and to the monitoring of apoptotic processes [61]. Furthermore, the development of the
high-speed, confocal, Raman microscope system [14,62,63] allows for the transient imaging of live
cells and the tracking of NMs within the cells.
By detecting the Raman features of NMs in biological matrices, it is possible to investigate the
behaviors of NMs, such as graphene [14]; carbon nanotubes [62-64]; polymer NMs [65]; and Au,
Ag, and SiO
2
NPs, due to their high Raman signals, resulting from high Raman cross sections, in
biological systems. It is possible for Raman spectroscopy to identify the proteins and ions adsorbed
by NMs without isolation in biological environments, despite a few report so far. The combined sys-
tem of Raman spectroscopy with AFM would provide other functions for the analysis of NMs in a
biological matrix. Monitoring the changes in the Raman signatures of cells or subcellular compart-
ments can provide information on cell metabolism due to interactions with NMs.
Liu et al. [64] performed
ex vivo
investigations of the long-term fate of polyethyleneglycol-
functionalized single-walled carbon nanotubes (SWCNTs) intravenously injected into mice. Raman
spectroscopy and Raman mapping were used to probe the blood circulation behavior and biodistri-
bution of the functionalized SWCNTs in various organs of the mice by exploiting the characteris-
tic resonant Raman spectrum of SWCNTs. The results showed the presence of the functionalized
SWCNTs in the intestine, feces, kidney, and bladder of mice, suggesting the excretion and clearance
of SWCNTs from mice via the biliary and renal pathways. No toxic effects from the functionalized
SWCNTs to mice were observed in necropsy, histology, and blood chemistry measurements despite
the long retention time, which is mostly due to the surface functionalization [66].
Andersson et al. [67] investigated the uptake and distribution of TiO
2
NPs (Figure 8.1) with
differences in size, shape, and crystal structure in the A549 cell line by TEM and Raman spectros-
copy. NP retention was found in the vicinity of organelles and the nucleus. The uptake of TiO
2
NPs
(Figure 8.2) was found to be slow, endosomal-particle uptake behavior, and strongly dependent on
the hard, agglomeration size rather than the primary particle size, which quantitatively agreed with
the measured intracellular oxidative stress.
A major advantage of Raman spectroscopy for the imaging and characterization of NMs in bio-
logical tissues lies in the possibility of using wavelengths in the near-infrared range for excitation.
The long penetration depth and the low autofluorescence in this spectral region allows for the Raman
imaging of whole, small animals [53]. Zavaleta et al. [68] reported the imaging of SWCNTs in
tumors in nude mice at a depth of 2 mm in the animal by monitoring the G-band peak (~1593 cm
−1
)
of SWCNTs.
In vivo
imaging enables the observation of the same animal over time. One shortcom-
ing of this technique is the poor spatial resolution (about 350 nm) focused by an ×100 optical lens
with numerical aperture of 0.9 [62], for finding NMs by the low-resolution optical microscope sys-
tem and for detections by the large laser spot size. The Raman spectroscopy technique enables one
to obtain the spatially resolved chemical fingerprinting of both NMs and biological components in
living cells and other biological organisms, which makes it possible to classify both the distribution
of NMs and their impact on biological systems. One disadvantage of the Raman technique is the
relatively low spatial resolution; the system normally uses optical microscope to observe a sample.
8.2.6 c
haracterIzatIoN
of
d
IssolutIoN
of
NM
s
IN
a
B
IologIcal
M
atrIx
The release of metal cations from NMs in the cell culture medium and the role of the metal cations
in cytotoxicity are still unclear. Many studies have attributed the toxic effects of metal-based NPs
primarily to released metal cations [9,69]. For example, Zn
2+
ions were assumed to release from ZnO
particles, as they were dispersed into cell culture medium or outside cells [70-72]. Consequently, the
toxic effect of ZnO NPs was mainly attributed to the dissolved Zn
2+
ions in the cell culture medium
[69,70]. By contrast, it was reported that the majority of ZnO NPs did not dissolve in bronchial epi-
thelial growth medium (BEGM) [73]. Furthermore, it was clearly shown that the toxicity of ZnO NPs
to human colon-derived RKO cells was independent of the amount of soluble Zn
2+
ions in the cell
culture medium [10]. In the case of CuO NPs, there are also contradicting reports of the contribution
