title: Not all that glitters is gold-Electron microscopy study on uptake of gold nanoparticles in Daphnia magna and related artifacts.
abstract: Increasing use of engineered nanoparticles has led to extensive research into their potential hazards to the environment and human health. Cellular uptake from the gut is sparsely investigated, and microscopy techniques applied for uptake studies can result in misinterpretations. Various microscopy techniques were used to investigate internalization of 10-nm gold nanoparticles in Daphnia magna gut lumen and gut epithelial cells following 24-h exposure and outline potential artifacts (i.e., high-contrast precipitates from sample preparation related to these techniques). Light sheet microscopy confirmed accumulation of gold nanoparticles in the gut lumen. Scanning transmission electron microscopy and elemental analysis revealed gold nanoparticles attached to the microvilli of gut cells. Interestingly, the peritrophic membrane appeared to act as a semipermeable barrier between the lumen and the gut epithelium, permitting only single particles through. Structures resembling nanoparticles were also observed inside gut cells. Elemental analysis could not verify these to be gold, and they were likely artifacts from the preparation, such as osmium and iron. Importantly, gold nanoparticles were found inside holocrine cells with disrupted membranes. Thus, false-positive observations of nanoparticle internalization may result from either preparation artifacts or mistaking disrupted cells for intact cells. These findings emphasize the importance of cell integrity and combining elemental analysis with the localization of internalized nanoparticles using transmission electron microscopy. Environ Toxicol Chem 2017;36:1503-1509. © 2016 SETAC.
authors.affiliation: Center for Electron Nanoscopy, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Louise Helene Søgaard
authors.initials: LHS
authors.lastname: Jensen
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Lars Michael
authors.initials: LM
authors.lastname: Skjolding
authors.affiliation: Department of Science and Environment, Roskilde University, Roskilde, Denmark.
authors.forename: Amalie
authors.initials: A
authors.lastname: Thit
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Sara Nørgaard
authors.initials: SN
authors.lastname: Sørensen
authors.affiliation: Department of Micro- and Nanotechnology, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Carsten
authors.initials: C
authors.lastname: Købler
authors.affiliation: Department of Micro- and Nanotechnology, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Kristian
authors.initials: K
authors.lastname: Mølhave
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Baun
mesh_terms: D000818:Animals; D016477:Artifacts; D003621:Daphnia / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D004064:Digestive System / Q000473:pathology; D016650:Fluorescein-5-isothiocyanate / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000633:toxicity; D008854:Microscopy, Electron; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence
chemical_list: D006046:Gold; D016650:Fluorescein-5-isothiocyanate
keywords: Aquatic invertebrate; Freshwater toxicology; Nanoparticle; Nanotoxicology