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Letter

Size and Surface Effects on the MRI Relaxivity of Manganese Ferrite Nanoparticle Contrast Agents

Supporting Info

Ulrich I. Tromsdorf,^†^# Nadja C. Bigall,^†^# Michael G. Kaul,^‡ Oliver T. Bruns,^§ Marija S. Nikolic,^† Birgit Mollwitz,^§ Ralph A. Sperling, Rudolph Reimer, Heinz Hohenberg, Wolfgang J. Parak, Stephan Förster,^† Ulrike Beisiegel,^§ Gerhard Adam,^‡ and Horst Weller*^†

Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany, Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany, Department of Biochemistry and Molecular Biology II: Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany, Ludwig-Maximilians-University, Center of NanoScience, Amalienstrasse 54, 80799 Munich, Germany, and Department of Electron Microscopy and Micro Technology, Heinrich-Pette Institute, Martinistrasse 52, 20251 Hamburg, Germany

Nano Lett., 2007, 7 (8), pp 2422–2427

DOI: 10.1021/nl071099b

Publication Date (Web): July 20, 2007

†

Institute of Physical Chemistry, University of Hamburg.

These authors contributed equally to this work.

‡

Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf.

Department of Biochemistry and Molecular Biology II: Molecular Cell Biology, University Medical Center Hamburg-Eppendorf.

Ludwig-Maximilians-University, Center of NanoScience.

Department of Electron Microscopy and Micro Technology, Heinrich-Pette Institute.

Corresponding author. E-mail: weller@chemie.uni-hamburg.de.

Abstract

Superparamagnetic MnFe₂O₄ nanocrystals of different sizes were synthesized in high-boiling ether solvent and transferred into water using three different approaches. First, we applied a ligand exchange in order to form a water soluble polymer shell. Second, the particles were embedded into an amphiphilic polymer shell. Third, the nanoparticles were embedded into large micelles formed by lipids. Although all approaches lead to effective negative contrast enhancement, we observed significant differences concerning the magnitude of this effect. The transverse relaxivity, in particular r₂*, is greatly higher for the micellar system compared to the polymer-coated particles using same-sized nanoparticles. We also observed an increase in transverse relaxivities with increasing particle size for the polymer-coated nanocrystals. The results are qualitatively compared with theoretical models describing the dependence of relaxivity on the size of magnetic spheres.

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