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| Titel |
Surface-enhanced Raman spectroscopy (SERS) to detect natural organic coatings on silver nanoparticles |
| VerfasserIn |
Melanie Kühn, Natalia P. Ivleva, Sondra Klitzke, Frank von der Kammer, Reinhard Niessner, Thomas Baumann |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107485
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| Publikation (Nr.) |
 EGU/EGU2015-10357.pdf |
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| Zusammenfassung |
| Applications for engineered inorganic nanoparticles (EINP) are rising and causing a higher
risk for EINP to be released into the environment. Their stability and transport behaviour
under environmental conditions is strongly depending on their surface properties which on
the other hand depend on the presence or absence of a surface coating. We assume that EINP
get coated soon after their release into the environment e.g. by humic substances like humic
or fulvic acids and NOM. Often EINP are stabilized by a coating agent like citrate or
polyvinylpyrrolidone. Therefore, the replacement of the initial coating material or a
multilayer coating has to be considered. Characterization of natural coatings on EINP is
crucial to predict their environmental behaviour, but analytical methods to investigate organic
coatings are scarce. To investigate humic- and fulvic acid coatings on silver nanoparticles (Ag
NP) Raman micro-spectroscopy (RM) was used. RM is limited in its sensitivity,
but silver nanoparticles cause an enhancement of the Raman signal of adsorbed
substances by a factor of 103-106, so called surface-enhanced Raman spectroscopy
(SERS).
The Raman spectrum of humic acids is dominated by the carbonaceous parts of the
humic acids which are known from carbon analysis and referred to as defect (D)
and graphite (G) peak of carbon. Humic acids of different origin (humic acid from
a lignite, suwannee river humic acid) showed differences in the D and G ratios
indicating a difference in the structure of the contained carbon. With SERS humic
and fulvic acid coatings on Ag NP were analysed: 1-100 mg/L humic acid stock
solution were mixed with citrate and hydroxylammoniumchloride stabilized Ag NP,
centrifuged and resuspended in deionized water (washing) to remove all coating
material not associated with Ag NP. This washing step was repeated up to four
times. SERS prooved that the coating was still present after the fourth washing
step. As SERS is only sensitive for substances in the immediate vicinity of the
surface (i. e., with a distance of less than 10nm) of the Ag NP, together with AF4
measurements which showed an increase of the diameter of a few nm between
uncoated and humic acid coated Ag NP, this indicates a thin but rather stable coating. |
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