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| Titel |
Investigation of Surface Coatings on Silver Nanoparticles by Surface Enhanced Raman Spectroscopy |
| VerfasserIn |
Melanie Kühn, Natalia P. Ivleva, Reinhard Niessner, Thomas Baumann |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078618
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| Zusammenfassung |
| The behavior of engineered inorganic nanoparticles (EINP) in the environment is strongly
affected by their surface properties. Once introduced in the aquatic or terrestric
environment, the nanoparticle surface may be altered by weathering or the formation of a
coating. These changes influence the interactions of the nanoparticle with natural
surfaces or interfaces as well as with other particles. Natural organic matter for
example is known to have a stabilizing effect on most nanoparticles. Therefore the
assessment of the fate and transport of nanoparticles in the environment requires a
precise knowledge of the influence of the coating and its modifications under natural
conditions.
A suitable tool for the investigation of coatings on silver nanoparticles is surface enhanced
Raman spectroscopy (SERS). Although silver nanoparticles themselves do not have a distinct
Raman signal, the Raman signal of adsorbed or nearby substances is enhanced by a factor of
103 - 106. This leads to a considerably higher sensitivity of SERS in comparison to normal
Raman microscopy. Therefore, coatings on silver nanoparticles should be accessible via the
SERS effect. As a first step, plain and citrate stabilized silver nanoparticles were mixed
with different natural coating substances (polygalacturonic acid, seaweed extract,
and humic substances) and filtered with a polycarbonate filter to remove excessive
coating material. Afterwards, the nanoparticles were redispersed from the filter by
ultrasonification. This washing procedure was repeated three times while always
maintaining the same concentration of nanoparticles. SERS spectra were recorded
after each washing step with a LabRAM HR Raman mircospectrometer (Horiba
Scientific, Japan, λ = 633 nm, 20x water-immersion-objective, measurement time
10Â s).
First results indicate the formation of a stabilizing layer around the nanoparticles after contact
with humic substances, thus providing experimental evidence to the stabilization
of EINP by humic substances on a μm level. At low concentrations of dissolved
humic substances, a specific SERS signal is only observed for coating materials
adsorbed to silver nanoparticles. This renders the method less sensitive to dissolved
potential coating substances. Furthermore, additional bands of coating which appear
in the SERS spectra due to chemical enhancement (charge transfer) indicate an
interaction of the used coating material with the nanoparticle. However, there is an
ambiguity between coatings on the nanoparticles and dissolved macromolecules in
the close vicinity of (but not attached to) nanoparticles which has to be resolved. |
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