Size and surface effects on the MRI relaxivity of manganese ferrite nanoparticle contrast agents.
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.
Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany.
Ulrich I
UI
Tromsdorf
Nadja C
NC
Bigall
Michael G
MG
Kaul
Oliver T
OT
Bruns
Marija S
MS
Nikolic
Birgit
B
Mollwitz
Ralph A
RA
Sperling
Rudolph
R
Reimer
Heinz
H
Hohenberg
Wolfgang J
WJ
Parak
Stephan
S
Förster
Ulrike
U
Beisiegel
Gerhard
G
Adam
Horst
H
Weller
D003287:Contrast Media / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D046911:Macromolecular Substances / Q000737:chemistry; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D017895:Manganese Compounds / Q000737:chemistry*; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods; D010316:Particle Size; D013499:Surface Properties; D017967:Zinc Compounds / Q000737:chemistry*
D003287:Contrast Media; D046911:Macromolecular Substances; D017895:Manganese Compounds; D017967:Zinc Compounds