title: Direct surface visualization of biofilms with high spin coordination clusters using Magnetic Resonance Imaging.
abstract: Magnetic Resonance Imaging is a powerful tool for the investigation of a biofilms' physical structure determining mass transport behavior which is of major importance in biofilm research. The entire biofilm is imaged in situ non-invasively and non-destructively on a meso-scale. In this study, different contrast agents were applied to study the biofilm's properties with the focus on mass transport, which is achieved by varying the contrast agents with respect to their NMR and interaction properties. The spatio-temporal tracking of these cluster, molecular and particulate contrast agents in biofilms was achieved by T1-, T2-weighted and proton density images during short (20h) and long (14 d) term exposures. The best biofilm surface visualization was observed when applying a new high spin coordination cluster (Fe10Gd10) showing a high affinity to the biofilm's surface and a fast immobilization within minutes. Contrarily, the small molecular contrast agents show no immobilization and fully penetrated into the biofilm. A concentration equilibrium was observed which was confirmed in back diffusion experiments. Interactions between larger nanoparticulate contrast agents and the biofilm required hours to achieve immobilization. Thus, the penetration depth into the biofilm is predominantly size-dependent. Here, it is shown that biofilm surface interactions can be observed in situ and spatio-temporarily resolved. The reported methodology demonstrates a new means to explore mass transfer of various substances in biofilms.
  
  
  CONCLUSIONS
  In biofilm research, the investigation of the biofilms' physical structure is of high relevance for the understanding of mass transport processes. However, commonly used imaging techniques for biofilm imaging such as CLSM or electron microscopy rarely visualize the real biofilm due to their invasiveness and destructiveness. Magnetic Resonance Imaging (MRI) represents the ideal tool to image the biofilm in situ, non-invasively and non-destructively with a spatial resolution of several 10μm. To gain specific structural and functional information, a variety of MRI contrast agents (molecular and particulate) was applied with different properties for the first time. Results elucidate the interactions between the biofilms' surface and the contrast agents and open a new field for biotechnological applications by functional contrast enhancement.
authors.affiliation: Pro(2)NMR, Institute for Biological Interfaces 4 and Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, Adenauerring 20b, 76131 Karlsruhe, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Ranzinger
authors.affiliation: Chair of Water Chemistry and Water Technology, Karlsruhe Institute of Technology, Engler-Bunte-Ring 1, 76131 Karlsruhe, Germany.
authors.forename: Maria P
authors.initials: MP
authors.lastname: Herrling
authors.affiliation: Chair of Water Chemistry and Water Technology, Karlsruhe Institute of Technology, Engler-Bunte-Ring 1, 76131 Karlsruhe, Germany; Urban Material Flow Management Technologies, Bauhaus-Institute for Infrastructure Solutions, Bauhaus University Weimar, Coudraystraße 7, 99423 Weimar, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Lackner
authors.affiliation: Institute of Inorganic Chemistry, Karlsruhe Institute of Technology, Engesserstr. 15, 76131 Karlsruhe, Germany.
authors.forename: Vanessa W
authors.initials: VW
authors.lastname: Grande
authors.affiliation: Institute of Inorganic Chemistry, Karlsruhe Institute of Technology, Engesserstr. 15, 76131 Karlsruhe, Germany; Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Amer
authors.initials: A
authors.lastname: Baniodeh
authors.affiliation: Institute of Inorganic Chemistry, Karlsruhe Institute of Technology, Engesserstr. 15, 76131 Karlsruhe, Germany; Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Annie K
authors.initials: AK
authors.lastname: Powell
authors.affiliation: Chair of Water Chemistry and Water Technology, Karlsruhe Institute of Technology, Engler-Bunte-Ring 1, 76131 Karlsruhe, Germany; DVGW Research Laboratory for Water Chemistry and Water Technology, Engler-Bunte-Ring 1, 76131 Karlsruhe, Germany. Electronic address: Harald.Horn@kit.edu.
authors.forename: Harald
authors.initials: H
authors.lastname: Horn
authors.affiliation: Pro(2)NMR, Institute for Biological Interfaces 4 and Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, Adenauerring 20b, 76131 Karlsruhe, Germany. Electronic address: Gisela.Guthausen@kit.edu.
authors.forename: Gisela
authors.initials: G
authors.lastname: Guthausen
mesh_terms: D018441:Biofilms; D001692:Biological Transport; D003287:Contrast Media / Q000737:chemistry; D003497:Cyclic N-Oxides / Q000737:chemistry; D004058:Diffusion; D005290:Ferric Compounds / Q000737:chemistry; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000737:chemistry; D010316:Particle Size; D013499:Surface Properties
chemical_list: D003287:Contrast Media; D003497:Cyclic N-Oxides; D005290:Ferric Compounds; D009942:Organometallic Compounds; C090600:gadobutrol; C000499:ferric oxide; C003959:TEMPO
keywords: Biofilm carrier; Contrast agents; Diffusion; Magnetic Resonance Imaging; Transport