title: Europium doping of superparamagnetic iron oxide nanoparticles enables their detection by fluorescence microscopy and for quantitative analytics.
abstract: BACKGROUND
  Pharmacokinetic studies and histological detection of superparamagnetic iron oxide nanoparticles (SPIO) in biomedical research are limited due to a high iron background especially in pathological tissues.
  
  
  OBJECTIVE
  The suitability of doping the iron oxide cores of SPIO with europium (Eu) was tested for improved histologic detection and for quantitative analysis without changing their properties as probes for magnetic resonance imaging (MRI). A special variant of SPIO, so called very small superparamagnetic iron oxide nanoparticles (VSOP), was used for this approach.
  
  
  METHODS
  VSOP, stabilized by a citrate coating, were synthesized with and without addition of Eu (Eu-VSOP and VSOP, respectively). MR signal enhancing effects of Eu-VSOP and VSOP were studied in vitro. Cellular uptake of Eu-VSOP and VSOP was examined in RAW264.7 cells. For Eu-VSOP, fluorescence microscopy and spectrophotometry were used. Eu fluorescence was enhanced by means of an antenna system. For VSOP, Prussian blue staining and photometry using the phenanthroline method were applied. Results for both VSOP variants were compared.
  
  
  RESULTS
  Eu-VSOP and VSOP did not differ with respect to MR signal enhancing effects nor to uptake characteristics in the RAW264.7 cell experiments. Fluorescence microscopy detects Eu-VSOP with higher sensitivity compared to light microscopy using Prussian blue staining. In microscopy as well as in the analytical quantification using fluorescence, detection of Eu-VSOP is not contaminated by Fe background.
  
  
  CONCLUSIONS
  Doping the VSOP with Eu allows for their improved detection by fluorescence microscopy and quantitative analysis without changing their cellular uptake characteristics or their MR signal enhancing effects and thus would allow for a multimodal approach for studying their pharmacokinetics and biodistribution in experimental research.
authors.affiliation: Department of Interventional and Diagnostic Radiology and Nuclear Medicine, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: Yuske
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Department of Radiology, Division of Experimental Radiology, Charité - Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Hauptmann
authors.affiliation: Department of Radiology, Division of Experimental Radiology, Charité - Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Kratz
authors.affiliation: Department of Radiology, Division of Experimental Radiology, Charité - Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Ebert
authors.affiliation: Wagner MSL Management, 15831 Mahlow, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Wagner
authors.affiliation: Department of Radiology, Division of Experimental Radiology, Charité - Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Taupitz
mesh_terms: D000818:Animals; D005063:Europium; D005290:Ferric Compounds / Q000737:chemistry*; D008279:Magnetic Resonance Imaging; D058185:Magnetite Nanoparticles / Q000032:analysis* / Q000737:chemistry; D051379:Mice; D008856:Microscopy, Fluorescence / Q000379:methods; D000067996:RAW 264.7 Cells / Q000737:chemistry / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D058185:Magnetite Nanoparticles; C000499:ferric oxide; D005063:Europium
keywords: Iron oxide nanoparticles; MRI; lanthanide luminescence; macrophage; molecular imaging