ARTICLE pubs.acs.org/JPCC
Relaxometric Studies of γ-Fe2O3@SiO2 Core Shell Nanoparticles: When the Coating Matters Sonia L. C. Pinho,†,‡ Sophie Laurent,§ Jo~ao Rocha,† Alain Roch,§ Marie-Helene Delville,‡ Stephane Mornet,‡ Luis D. Carlos,† Luce Vander Elst,§ Robert N. Muller,*,§,^ and Carlos F. G. C. Geraldes*,|| †
Departments of Chemistry and Physics, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal CNRS, Universite de Bordeaux, ICMCB, 87 avenue du Dr. A. Schweitzer, Pessac, F-33608, France § Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, B-7000 Mons, Belgium ^ Center for Microscopy and Molecular Imaging, Rue Adrienne Bolland 8, B-6041 Charleroi, Belgium Department of Life Sciences, Faculty of Science and Technology, and Center of Neurosciences and Cell Biology, University of Coimbra, 3001-401 Coimbra, Portugal
)
‡
ABSTRACT: Iron oxide nanoparticles with a constant superparamagnetic core coated with a silica shell with a thickness ranging from 0.6 to 71 nm were prepared by a fast and facile soft chemistry approach. The increase of the coating thickness of the γ-Fe2O3@SiO2 nanoparticles causes a significant decrease of the r1 and r2 relaxivities of their aqueous suspensions. The sizes of the nanoparticles obtained by relaxometry are significantly lower than those measured by electron microscopy. Their magnetizations measured by relaxometry also decrease relative to the values obtained by magnetometry, which correspond to the core. However, this “magnetic dilution” is smaller than expected if the entire silica shell was water impermeable. Both results indicate that a significant part of the silica coating is permeable to water. The adequate silica shell thickness may, thus, be tuned to allow for both a sufficiently high response as contrast agent and an adequate grafting of targeted biomolecules.
’ INTRODUCTION In the past few years, bioapplications of magnetic nanoparticles have been widely developed with regard to their abilities for magnetic resonance imaging (MRI),1 hyperthermia,2 bioassays,3 and drug or biomolecules transport.4 Coreshell structures and multifunctional nanoparticles that can carry several components with different functionalities are vital for these applications. With the development of novel advanced nanoparticles (NPs) applications emerges the need for the synthesis of well-controlled size and morphology NPs. Among their numerous applications, superparamagnetic iron oxide NPs (USPIO), used in biomedical research, have been developed for diagnosis and therapy.1,518 In the context of magnetic resonance imaging (MRI), USPIOs (
