Biomedical Engineering Reference
In-Depth Information
after the NM suspension is centrifuged. However, it deserves to be pointed out that the elemental
concentration obtained by ICP-based techniques can be affected by free ions and by the ions that
result from the decomposition of matter at the very high temperatures and/or acid environments
present for an ICP-based measurement. That is, after the sample is injected for ICP-based measure-
ment, the plasma's extreme temperature or strong acid causes the sample to separate into individual
atoms (atomization); these atoms are then ionized (M → M
+
+ e
−
) so that they can be detected by the
mass spectrometer. As a result, the digestion procedures involved in ICP-based techniques make it
almost impossible to differentiate the ions formed as a result of the dissolution of materials from the
NMs per se. We found by TEM that the removal of NMs, such as ZnO NPs, by centrifugation, the
procedure currently used for the estimation of the released ion concentration, was incomplete even at
a relative centrifugal force of 150,000
g
[83]. Thus, the Zn concentration in supernatant as measured
by ICP-based methods cannot be regarded as the concentration of free Zn
2+
ions, which were released
from ZnO NPs in cell culture medium. We also found that the toxic contribution of Zn
2+
ions released
from ZnO NPs to the A549 cell lines was estimated to be only about 10%.
There are other techniques used to study NMs in a biological matrix. Synchrotron microfocused
x-ray fluorescence (μ-XRF) and micro-x-ray absorption near-edge structure (μ-XANES) were used
to study the chemical form and localization of titanium in cucumber plants treated with TiO
2
NPs
[84], the form of CeO
2
in the roots of corn seedlings [85], and the forms of Zn and Ce within soy-
bean tissues that were obtained from the soybeans grown in organic farm soil spiked with ZnO or
CeO
2
NPs [86]. A quantitative photoacoustic technique is being developed to image NMs in cells
and tissues [87]. Multifocal two-photon microscopy was used to track gold nanorods in cells [88].
However, the resolution of the μ-XRF and μ-XANES is generally at the micrometer level. The
signals of the other two techniques are mostly dependent upon the characteristics of NMs, nonplas-
monic NMs for photoacoustic imaging, and plasmonic NMs for two-photon microscopy.
8.3 CONCLUSION
The characterization of NMs in a biological matrix, while preserving the spatial information and
chemical components, is very challenging. An inappropriate analytical method can strongly influ-
ence the interpretation of the experiment, and does not provide information on the direct relevance
from a toxicological perspective. The further progress of nanotoxicology requires breakthroughs
in analytical methods for the accurate tracking, detecting, and identifying of NMs as well as their
transformation in biological matrices and interactions with biological systems.
In this chapter, we have proposed a nomenclature for NMs collected from the existing litera-
ture and based on our own experience for the accurate description and characterization of NMs.
We have emphasized the advantages and shortcomings of the techniques commonly used for the
characterizations of size, shape, chemical composition, and electronic/optical properties of NMs in
a dry form. There is no direct method for the investigation of the dissolution of NMs in biological
environments. At this moment, we believe that electron microscopy and Raman spectroscopy are
among the most appropriate techniques for the characterization of NMs in biological matrices.
Hopefully, this chapter is a useful guide to the choice of analytical methods to characterize NMs,
not only in a dry form, but also in a biological matrix, and mostly promoting the development of new
techniques and methods for the
in situ
characterization of NMs in biological matrices.
ACKNOWLEDGMENTS
This work was partially supported by the Program of International S & T Cooperation (No.
2013DFG52800)
,
by Zhejiang Provincial Natural Science Foundation (Youth Talent Program:
R4110030), Science and Technology Department of Zhejiang Provincial (Qianjiang Talent Program:
2011R10077), by Program for New Century Excellent Talents in University (NCET-12-0494) of
China, by the Interdisciplinary Laboratory for Nanoscale Science and Technology of National
