Biomedical Engineering Reference
In-Depth Information
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Position [°2 theta] (copper (Cu))
Position [°2 theta] (copper (Cu))
FIGURE 1.7
X-ray diffraction analysis (XRD) spectra of silica nanoparticles (NPs)
(NanoGEM.SiO
2
.FITC) amorphous form and silver NPs (NanoGEM.Ag_50.EO) crystalline
form.
silica is benign, while its crystalline form is cytotoxic and carcinogenic) (Borm
et al. 2001). Thus, the crystallinity of a nanomaterial should always be evaluated.
The crystal structure of an NOAA can be determined by X-ray diffraction analysis
(XRD) (see Figure 1.7).
The XRD is useful for distinguishing different crystal phases of materials of the
same chemical composition and can be used to determine the average crystallite size
and shape. Microscopy methods, such as the AFM, SEM, and TEM, can also be used
to assess the crystallite size, which for monocrystalline primary particles also means
average primary particle size.
An analysis of nanomaterial composition should be undertaken with special
attention to possible impurities. Contamination can appear at any stage of nanomate-
rial production, handling, or sampling. Impurities can be delivered from reagents,
not sufficiently cleaned laboratory equipment, or handling vessels. Methods mostly
used for the detection of impurities are the Fourier transform infrared spectroscopy
(FTIR), XPS, and SIMS. For biological evaluation of a nanomaterial, impurities may
have an influence if they are present in sufficient quantity. Thus, before any studies
on a nanomaterial, not only the composition of the possible impurities but also their
quantity should be detected.
1.7 SURFACE CHEMISTRY
Chemical composition of the outermost layers of a nanomaterial highly defines
its energy and reactivity. Surface chemistry is critically important with respect
to nanomaterial agglomeration, aggregation, or interaction with its surroundings.
Tailoring surface chemistry of nanomaterials with well-controlled surface coat-
ings/functionalities enables their broad application. It is highly promising that
nano-objects may have more and more adaptations in therapy, medicine delivery,
or diagnostics. However, identification and quantification of the functional groups
linked to the surface of NOAAs are very challenging due to the fact that they
are coated with only a little amount of small molecules. Techniques applicable
for identifying the surface composition and atomic arrangement on the surface of
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