Nanoparticles for Bioimaging: Analytical Characterization and Measurements - Nanotechnology for Biomedical Imaging and Diagnostics - page 151

figure 6.3 an example of an energy-dispersive X-ray spectrograph collected using an
EDaX genesis system.

a very different elemental analysis method is energy-dispersive X-ray spec-
troscopy (EDS) . This technique is commonly used in concert with electron
microscopy where the electron beam from a scanning electron microscope or
transmission electron microscope is used to excite a solid sample, which then
emits X-rays that are detected as an electrical signal. The X-rays are emitted from
the sample with energy characteristic to each element found within the sample.
an example of an energy-dispersive X-ray spectrograph collected using an EDS
system is shown in figure 6.3. This technique is able to detect most elements
heavier than beryllium, including carbon, nitrogen, and oxygen. The detection
limits for EDS are significantly higher than those for atomic spectroscopy tech-
niques as elements that compose less than 10% of a sample by weight may be
indistinguishable from background noise. Quantitative analysis by EDS allows
for the relative percent composition of a sample to be determined. EDS signals are
sensitive to sample height, and the best results are achieved on smooth polished
surfaces. Particle samples should be dispersed evenly on a flat surface for analysis
and may exhibit a 5% or greater measurement variance. EDS is often used for
elemental mapping of solid samples; however, this feature is rarely useful for
nanoparticle studies as the spatial resolution of EDS is measured in microns and
not nanometers.

6.3 size aNalysis

as material properties at the nanoscale often differ from properties at micro- and
macroscales, great attention is often paid to particle sizing analysis. Imaging tech-
niques can provide information both about the size and morphology of particles,
while statistical techniques such as dynamic light scattering (DlS) provide more
information about a particle's stability in a fluid and the distribution of particle sizes
in the sample.