title: Investigation of coatings of natural organic matter on silver nanoparticles under environmentally relevant conditions by surface-enhanced Raman scattering.
abstract: The widespread use of engineered inorganic nanoparticles (EINP) leads to a growing risk for an unintended release into the environment. Despite the good characterization of EINP in regard to their function scale and the application areas, there is still a gap of knowledge concerning their behaviour in the different environmental compartments. Due to their high surface to volume ratio, surface properties and existence or development of a coating are of high importance for their stability and transport behaviour. However, analytical methods to investigate organic coatings on nanoparticles in aqueous media are scarce. We used Raman microspectroscopy in combination with surface-enhanced Raman scattering (SERS) to investigate humic acid coatings on silver nanoparticles under environmentally relevant conditions and in real world samples. This setup is more challenging than previous mechanistic studies using SERS to characterize the humic acids in tailored settings where only one type of organic matter is present and the concentrations of the nanoparticles can be easily adjusted to the experimental needs. SERS offers the unique opportunity to work with little sample preparation directly with liquid samples, thus significantly reducing artefacts. SERS spectra of different natural organic matter brought into contact with silver nanoparticles indicate humic acid in close proximity to the nanoparticles. This coating was also present after several washing steps by centrifugation and resuspension in deionized water and after an increase in ionic strength.
authors.affiliation: Technische Universität München, Institute of Hydrochemistry, Marchioninistr. 17, D-81377 Munich, Germany. Electronic address: melanie.kuehn@tum.de.
authors.forename: Melanie
authors.initials: M
authors.lastname: Kühn
authors.affiliation: Technische Universität München, Institute of Hydrochemistry, Marchioninistr. 17, D-81377 Munich, Germany. Electronic address: natalia.ivleva@ch.tum.de.
authors.forename: Natalia P
authors.initials: NP
authors.lastname: Ivleva
authors.affiliation: University of Freiburg, Institute of Forest Sciences, Chair of Soil Ecology, D-79085 Freiburg, Germany; Technische Universität Berlin, Department of Soil Science, Ernst-Reuter-Platz 1, 10587 Berlin, Germany. Electronic address: sondra.klitzke@tu-berlin.de.
authors.forename: Sondra
authors.initials: S
authors.lastname: Klitzke
authors.affiliation: Technische Universität München, Institute of Hydrochemistry, Marchioninistr. 17, D-81377 Munich, Germany. Electronic address: reinhard.niessner@ch.tum.de.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Niessner
authors.affiliation: Technische Universität München, Institute of Hydrochemistry, Marchioninistr. 17, D-81377 Munich, Germany. Electronic address: tbaumann@tum.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Baumann
mesh_terms: D053768:Metal Nanoparticles / Q000737:chemistry*; D008956:Models, Chemical; D012834:Silver / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D013499:Surface Properties
chemical_list: D012834:Silver
keywords: Coatings; Engineered inorganic nanoparticles; Natural organic matter; Surface-enhanced Raman scattering