Mastering the Shape and Composition of Dendronized Iron Oxide

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Mastering shape and composition of dendronized iron oxide nanoparticles to tailor magnetic resonance imaging and hyperthermia Aurélie Walter, Claire Billotey, Antonio Garofalo, Corinne Ulhaq-Bouillet, Christophe Lefevre, Jacqueline Taleb, Sophie Laurent, Luce Vander Elst, Robert N. Muller, Lenaic Lartigue, Florence Gazeau, Delphine Felder-Flesch, and Sylvie Begin-Colin Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/cm5019025 • Publication Date (Web): 25 Aug 2014 Downloaded from http://pubs.acs.org on August 26, 2014

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Chemistry of Materials

Mastering shape and composition of dendronized iron oxide nanoparticles to tailor magnetic resonance imaging and hyperthermia. Aurélie Walter1, Claire Billotey2*, Antonio Garofalo1, Corinne Ulhaq-Bouillet1, Christophe Lefèvre1, Jacqueline Taleb2, Sophie Laurent3, Luce Vander Elst3, Robert N. Muller3, Lénaïc Lartigue4, Florence Gazeau4, Delphine Felder-Flesch1* and Sylvie Begin-Colin1* 1

Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS, Université de Strasbourg, 23, rue du Loess, BP 43, 67034 Strasbourg Cedex 2 (France)

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Laboratoire de Physico-Chimie des Matériaux Luminescents, UMR 5620 CNRS-UCBL, Université Claude Bernard Lyon 1, 10 rue Ada Byron 69622 Villeurbanne cedex, France. Hospices Civils de Lyon - Service de Médecine Nucléaire Pavillon B, 5 place d’Arsonval, 69437 Lyon cedex 03, France 3

General, Organic, Biomedical Chemistry; NMR and Molecular Imaging Laboratory. Université de Mons. 19 Avenue Maistriau, B-7000 Mons, Belgium; Center for Microscopy and Molecular Imaging (CMMI), 6041 Gosselies, Belgium 4

Laboratoire Matière et Systèmes complexe, UMR 7057, CNRS, Université Paris 7 Diderot, 75205 Paris Cedex 13, France

Iron oxide; cubic nanoparticles; core-shell; MRI; hyperthermia ABSTRACT: The current challenge in the field of nanomedicine is the design of multifunctional nano-objects efficient both for the diagnostic and the treatment of diseases. Here, dendronized FeO1-x@Fe3-xO4 nanoparticles with spherical, cubic and octopode shapes and oxidized Fe3-xO4 nanocubes have been synthesized and structurally and magnetically characterized. Strong exchange bias properties are highlighted in core-shell nanoparticles due to magnetic interactions between their antiferromagnetic core and ferrimagnetic shell. Both in vitro relaxivity measurements and NMRD profiles have confirmed the very good in vitro MRI properties of core-shell and cubic shape NPs, especially at low concentration. This might be related to the supplementary anisotropy introduced by the exchange bias properties and the cubic shape. The high heating values of core-shell nanoparticles and oxidized nanocubes at low concentration are attributed to dipolar interactions inducing different clustering state as function of concentration. In vivo MRI studies have also evidenced a clustering effect at the injection point depending on the concentration and confirmed the very good in vivo MRI properties of core-shell nanoparticles and oxidized nanocubes in particular at low concentration. These results show that these core-shell and cubic shape dendronized nano-objects are very suitable to combine MRI and hyperthermia properties at low injected dose.

Introduction Some of the most significant and promising applications for magnetic iron oxide nanoparticles (NPs) lie in the fields of biology and biomedicine. The continuous growth of nanotechnology has brought challenging innovations in the design and synthesis of nanovectors for medicine, able to revolutionize the field of diagnosis and therapy. Indeed, concerning the synthesis and functional-

ization of inorganic NPs for biomedical applications, most researchers aim now at developing multifunctional theranostic (i.e. including therapeutic and diagnostic functions) NPs which can both identify disease states and deliver therapy 1,2,3,4,56,7,8,9 and thus allow a therapy followup through imaging. To develop such theranostic iron oxide based nano-objects, several challenges are still to be overcome such as i) the design of functionalized NPs

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allowing an efficient imaging through high MRI contrast enhancement combined to an efficient therapy achieved by hyperthermia, ii) the design of a robust multifunctional organic coating bearing different functions allowing imaging, targeting and drug delivery while ensuring furtivity, suitable biodistribution and bioelimination and iii) in vitro and in vivo validations of their efficiency. Functionalized iron oxide NPs are commercially used as contrast agent (CAs) for MRI and the development of new MRI agents represents a valuable market. Ultra small iron oxide NPs are of particular interest as biodegradable and non-toxic nano-objects compared to other CAs families. 10,11 To be used as CAs, NPs should exhibit high saturation magnetization and be functionalized with molecules favoring water diffusion around and close to the magnetic core and leading to biocompatible stable suspensions in physiological media with an average hydrodynamic size smaller than 100 nm ensuring a high circulation time in the blood.9 Iron oxide NPs are also developed for magnetic hyperthermia (MH). When exposed to alternating magnetic fields of appropriate amplitude and frequency, these NPs release heat locally (where they are concentrated), which reduces the cancer cells viability. The favourable recent results of the “Nanothermotherapy” study in clinical phase II led by a German company MagForce Nanotechnology (hospital Charité in Berlin) 12,13 demonstrated the MH potential. Indeed, MH is shown to enhance the tumor cells sensitivity towards chemo or radio-therapy. Furthermore MH facilitates drug release or acts on cell membranes.14 The current positive impact of MH in therapy will allow us to expect great breakthroughs in biomedical science. One of the main limitations of MH is the low heating power of currently used magnetic NPs, requiring a local injection of large quantities of NPs. There is thus a great challenge for optimizing the heating power of magnetic NPs. The amount of heat generated by NPs is highly dependent on the NPs structural and magnetic properties. First studies have shown that spherical iron oxide NPs with a mean size around 20 nm are suitable for clinical MH.15 However the current progress in the NPs synthesis allows now the synthesis of NPs with variable and controlled shapes and core-shell structures. A very important anti-tumor effect induced by MH has been thus noticed with core-shell NPs consisting of a core displaying a high magnetic anisotropy surrounded by a shell with a small magnetic anisotropy.16 Another strategy for increasing the NPs heating power is to play on their shape and nanostructure therefore affecting their magnetocrystalline anisotropy or enabling cooperative magnetism. For instance iron oxide cubic 17 and flower 18 shaped NPs have recently shown considerably improved MH properties compared to optimized 20 nm spherical iron oxide NPs. Various synthesis methods have been reported for the preparation of iron oxide magnetic NPs such as coprecipitation, hydrothermal, sol gel or polyol methods.19,20,21 The synthesis by thermal decomposition of met-

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al complexes in a high boiling solvent in the presence of surfactants appears to be the most appropriate because it allows a fine control of the NPs size, morphology and composition.22,23 This method opens the possibility to study the influence of these parameters on MRI and hyperthermia properties. Few studies have been reported so far on the influence of the shape and composition of iron oxide NPs on the MRI properties. The transverse relaxivity (r2) of spherical and faceted iron oxide NPs of various sizes were intensively studied and compared.24,25,26,27,28,29 The increase of r2 values with the NPs size was ascribed to the concomitant saturation magnetization increase. Faceted NPs have also been shown to display higher r2 values than spherical NPs 24,28 proving that the crystal shape does influence the anisotropy energy and thus the relaxivities. Unlike the studies of Smolensky et al.23 and Joshi et al27 in which the morphology of the faceted NPs was not homogeneous, N. Lee and al.30,31 reported a very high r2 relaxivity with well-defined ferrimagnetic cubic iron oxide NPs by tuning both size and shape. The influence of the NPs composition on the relaxation properties has also been investigated. Spinel structures with various compositions (MnFe2O4, CoFe2O4, NiFe2O4) have been compared to the standard Fe3-xO4 NPs contrast agents.29,32 Here also the highest r2 values were related to the highest saturation magnetization, namely for MnFe2O4. Among core - shell structure, to the best of our knowledge, the only system which has been investigated is iron@iron oxide core–shell NPs.33,34,35 The presence of a pure iron core enhanced the saturation magnetism and thus the r2 relaxivity which was higher than for standard iron oxide NPs even at low iron concentration.33 These structures were shown to exhibit also interesting Specific Absorption Rate (SAR) values. Worthy to note is that the transverse relaxation is affected by the aggregation state of magnetic NPs. As the aggregation proceeds, the r2 relaxivity value was reported first to increase with agglomeration size, to reach a maximum and then to decrease.36,37 Thus a fine control of the final magnetic particle size after functionalization and of the clustering of NPs is also important to reach optimal conditions (e.g. high contrast/r2) for MRI. Herein, magnetic nano-objects with designed core-shell composition and shapes able to combine MRI and MH have been synthesized. The structural and magnetic properties of spherical, cubic and octopodes shaped coreshell NPs with an antiferromagnetic (AFM) Fe1-xO core and a ferrimagnetic (FIM) spinel Fe3-xO4 shell have been described. Core-shell NPs combining AFM and FIM materials have been shown to display exchange bias properties 38 which results in the modification of the magnetocrystalline energy to which is ascribed a supplementary term referring to the FIM/AFM interface. After their synthesis, these nano-objects are dendronized i.e functionalized with a small branched molecule (dendron) in order to obtain stable water suspensions. Indeed dendronized iron oxide NPs have been earlier demonstrated to be very

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suitable T2 contrast agents with a good bioelimination.39,40,41,42 Then, the effect of such core-shell magnetic NPs structure on both hyperthermia and MRI properties is investigated and compared to that of oxidized nanocubes. To the best of our knowledge, the MRI and hyperthermia properties of Fe1-xO@Fe3-xO4 core shell structures have not been reported so far. Further, we address the challenge to demonstrate that ferrite as a shell capped on a Fe1-xO antiferromagnetic core is also able to display powerful MRI properties. The high contrast enhancement properties of these core-shell structures and of oxidized nanocubes are highlighted by in vivo MRI studies as a function of iron concentration. Coreshell NPs and oxidized nanocubes are shown to display combined MRI and hyperthermia properties at low iron concentration related to clustering effect induced by their anisotropy and dipolar interactions.

at 110°C in absence of a reflux condenser and then the solution was quickly heated to 220°C and maintained at this temperature for 10 min. But then the synthesis mixture was heated at a faster rate (5°C/min) than in the case of cubic nanoparticles and temperature was maintained at 320°C for 1h. The resultant black solution was then cooled to room temperature, and the NPs were washed several times by addition of ethanol and by centrifugation (14000 rpm, 10min). The edges grown cubic NPs or octopodes, named NO24, were easily suspended in THF. Oxidation of the nanocubes (oxNC16) 50 mg of cubic nanoparticles NC16 were dispersed in toluene and heated to reflux during 48h while bubbling air inside the suspension. After this post synthesis oxidation step, the nanoparticles were dispersed and stored in THF after toluene evaporation. After oxidation the NCs are named oxNC16. Synthesis of the dendron molecule and dendronization of NPs

Experimental Section Synthesis of spherical nanoparticles (NS19) Spherical core shell FeO@Fe3O4 NPs were synthesized by thermal decomposition of iron stearate complex in the presence of oleic acid in a high boiling point solvent. 1.38 g (2.2mmol) of Fe (stearate)2 (9.47% Fe, Strem Chemicals) and 1.25g (4. 4 mmol) of oleic acid (OA) (99%, Alfa Aesar) were added to 18g of docosene (99% Fluka, b.p 355°C). The mixture was heated at 110°C in absence of a reflux condenser for 1 hour to evaporate the traces of unwanted solvent and to dissolve the reactants. The solution was then heated to 355°C with a heating rate of 5°C/min and refluxed for 120 min at this temperature under air. The resultant black solution was then cooled to room temperature, and the NPs were washed several times by addition of ethanol and by centrifugation (14000 rpm, 10min) (50ml oak ridgecentrifuge tubes, FEP, Thermo Scientifc, Rochester). The nano spheres, named NS19, were easily suspended in THF. Synthesis of nanocubes (NC16) The cubic nanoparticles were synthesized according to Pichon et al [43]. 2.08g (2.32mmol) of iron oleate, 0.705g (2.32 mmol) of sodium oleate and 0.2 mL (0.65 mmol) of oleic acid were added to 15 mL of octadecene (b.p 318°C). The mixture was first heated at 110°C in absence of a reflux condenser, and then the solution was quickly heated to 220°C and maintained at this temperature for 10 min. Then the solution was heated at a rate of 1°C/min up to 320°C and was refluxed for 1h under argon. The resultant black solution was then cooled to room temperature, and the NPs were washed several times by addition of ethanol and by centrifugation (14000 rpm, 10min). The nano cubes, named NC16 were easily suspended in THF. Synthesis of octopodes (NO24) To synthesize edges grown cubic nanoparticles, the same synthesis mixture as in the case of cubic nanoparticles was prepared. As earlier, the mixture was first heated

A hydrophilic oligoethyleneglycol-derivatized dendron (Dcooh) displaying a phosphonic acid at the focal point together with a long and functional octaethyleneglycol chain in para position has been synthesized according to an 11 steps sequence. Compared to our previously reported dendritic coatings 43,39,42,40 we introduced a linker between the dendritic hydrophilic part and the phosphonic acid focal point mainly to facilitate the dendron anchoring at the NP surface and increase the grafting rate. The synthesis of the dendron molecule is described in SI. The scheme of the dendron Dcooh used to functionnalize the NPs is depicted in Scheme 2 in SI and Figure SI 3b. The different types of nanoparticles (NPs) were functionalized with Dcooh through a direct grafting process. The same procedure was applied for the different NPs: 40 mg of NPs were dispersed in THF at a concentration of 1 mg/mL and were mixed to 10 mg of dendron molecule Dcooh and magnetically stirred (350 rpm) for 24h. After this period, the suspensions were purified by ultrafiltration. The THF suspension was introduce in the apparatus and purification occurred by pressurizing the solution flow. The solvent and un-grafted molecules (released oleic acid and Dcooh molecule excess) went through the membrane while grafted nanoparticles did not. The particles were then re-dispersed in 20mL. This operation was repeated 3 times. After purification, 10 mg of dendron Dcooh were added to the purified suspension, and the suspension was magnetically stirred for another 24h. The nanoparticles were then precipitated by adding hexane. After centrifugation (8000 tr/min, 3 min), the grafted particles were easily re-dispersed in distilled water. Characterization of dendronized NPs The grafting step was confirmed by infrared spectroscopy using a Fourier Transform Infrared (FTIR) spectrometer (Digilab FTS 3000). The grafting rate was determined by elemental analysis. The stability of the dendronized NPs suspensions was

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assessed by measuring the particle size distribution in water. Hysteresis cycles at room temperature, at 5K and ZFC/FC measurements between 5K and 300K under a field of 75 Gauss and at 5K after a cooling under an applied field of 2T, of as synthesized NPs were performed with a Superconducting Quantum Interference Device (SQUID). The NP@OA were characterized by X-ray diffraction (XRD) using a Bruker D8 Advance equipped with a monochromatic copper radiation source, (Kα = 0.154056 nm) and a Sol-X detector in the 25-65° range with a scan step of 0.03°. High purity silicon powder (a=0.543082 nm) was systematically used as an internal standard. All the diffraction patterns were analysed by the Rietveld method using the Fullprof program64 for which the modified Thompson-Cox-Hasting pseudo-Voigt profile function was chosen to generate the line shape of the diffraction peaks.44 Hyperthermia measurements Magnetic hyperthermia measurements were conducted with two experimental set-ups. Measurements at a field frequency of 700 kHz with a field amplitude of 27 mT (21 kA/m) were obtained using a laboratory-made device previously described46. It consists of a resonant RLC circuit with a 16 mm coil. The coil and the sample were thermalized at 37°C. The temperature was probed with a fluoro-optic fiber thermometer (Luxtron STF-2, BFiOPTiLAS SAS). This measurement was performed on oxNC16, NS19 and NC16 samples and the iron concentration was varied from 2 mM to 70mM. The field dependency of the heating power was conducted at the center of a coil producing an oscillating magnetic field of frequency 198 kHz and the field amplitude was adjusted in the range of 12mT to 45mT. In order to generate the alternating current, the coil was connected to an induction generator (Celes inductor C97104) and the sample was thermalized at 37°C. Measurements were performed on oxNC16 and NS19 samples with an iron concentration of 65 and 72 mM, respectively. In both case, the specific loss power (SAR) was calculate using the equation SAR= (CwaterVs/m)*(dT/dt), where Cwater is the volume specific heat capacity of the water (Cwater = 4185 J.L-1.K-1), the nanoparticles contributions are neglected. VS is the volume of the sample (VS = 300 μL or 250 μL for the measurement performed respectively in the first or in the second experimental setup). NMRD profiles Proton NMRD profiles were recorded using a Stelar Fast Field Cycling relaxometer (Mede, Italy). The system operates over a range of magnetic field extending from 0.25 mT to 0.94 T (0.01-40 MHz) at 37°C. T1 and T2 measurements were performed on Bruker Minispectrometers mq20 and mq60 (Karlsrushe, Germany) working at a

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Larmor frequency of 20 MHz (0.47T) and 60 MHz (1.41T) at 37°C. In vitro and in vivo MRI studies In order to assess the oxidized cubic NPs (oxNC16) as MRI contrast agent, and evaluate its biokinetics and biostability, we assessed the MR contrast effect in vivo in rats using a small animal dedicated 7T MR Biospec™ system (Brüker, Wissenbourg, France) equipped with 400 mT/m gradient under gaseous anesthesia (Isoflurane®, LaboratoireBelamont, Neuilly-sur-Seine, France) using experiment protocols approved by the local animal ethic committees. In order to improve the quality of the vascular distribution after intra-venous injection, a catheter inside a saphen vein was implanted in each rat before MRI studies. MR contrast effects were assessed with both multi- gradient echo sequence T1 (repetition time (TR) = 800msec, 12 echos- echo spacing = 2.56 msec – 1st echo time (TE) = 1.54 msec, 2 mm section thickness, 10x7 cm field of view, 256x128 matrix) and rapid echo sequence T2 ([TR/TE = 800/9.1 ms]; flip angle=180°, 3 mm section thickness, 10x10 cm field of view, 256 x 256 matrix) weighted dynamic sequences triggered on respiration (Rapid Biomedical GmbH) constituted by 4 to 6 about 90 sec (T2w.) to 2.3-3 min (T1w.) coronal slices centered on kidneys, bladder, liver and aorta and acquired before and over 1h after injection of 300 to 900 microliters (3.9.10-4 to 1.16.10-3 mmoles of iron) of sterilized oxNC16. The mean value signal (S) was measured at each time point in Region Of Interest (ROI) corresponding to aorta, liver, kidneys (whole organ and/or renal cortex, and urinary intra-renal excretion cavities called “pyelon”) and bladder. In order to quantify the in vivo MR contrast effect of oxNC16 as function of iron mass injected, postinjection delay, the contrast enhancement (EHC) related to the focal dendronized particles deposition was calculated in each ROIs as defined: EHC = [SN(t) – SN(bi)/ SN (bi)]. In order to better analyze the in vivo MR contrast effects, the in vitro measurements were also performed with the same MR system at room temperature on 17 one cm3 iron samples of oxNC16 dispersed in water at 2.4.10-2 to 7.5.10-1 mol.l-1 iron concentration and compared to a water sample. The T1 and T2 relaxation times of each sample were determined using an inversion recovery FLASH (IRFLASH) imaging sequence with varying IR time (Biospec System 70/20, Brucker, Ettlingen, Germany), allowing to calculate the spin-lattice (R1) and spin-spin (R2) relaxivities defined as the concentration-independent measures of the relaxation rate enhancement for respectively the longitudinal and transverse magnetization components.

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Figure 1. TEM (inset: HRTEM) images of NPs: a) NS19, b) NC16, c) NO24 and d) oxNC16.Dashed lines delimitate the Fe1-xO core and strait lines delimitate the Fe3-xO4 shell

In order to assess respectively the in vitro T1 and T2 contrast effects of the oxNC16 dispersed in a water solution, the signal of each samples were measured on 2 mm axial slices acquired respectively with standard spin-echo sequence [TR/TE = 500/12 ms] and multi- spin echo sequence [TR/TE = 2000/70 ms] to calculate the EHC in reference to the water [EHC (%)w= [(((Signal value of dendronized NPs) – (signal value of water))/signal value of water)x 100]. Results 1. Structural and magnetic characterizations of the NPs Spherical, cubic and octopode-shaped NPs were synthesized by thermal decomposition by varying the ligand nature (oleic acid and/or sodium oleate) and the heating rate. According to earlier studies,45,46 a large amount of oleate favors a reducing environment and induces the formation of core-shell NPs with a Fe1-xO core and a Fe3xO4 shell. Core-shell nanocubes were also oxidized to compare the properties of both Fe1-xO @Fe3-xO4 core-shell and oxidized nanocubes. Figure 1 shows transmission electron microscopy (TEM) images of the different NPs. The mean size, determined by measuring at least 100 nanoparticles on the TEM images, is 19 nm (±15%) for nanospheres (NS19), 16 nm (± 12%) for nanocubes (NC16) and 24 nm (±11%) for octopodes (NO24). The mean size corresponds to the mean NPs diameter for NS19, to the mean edge length for NC16, and

to the length between two corners for NO24. In the case of oxidized NCs (oxNC16) (Figure 1D), the oxidation step does not modify the morphology and size of NPs. After the oxidation step, NC16 were called oxNC16. TEM and HRTEM images (Figure 1A to 1C) show a slight contrast difference between core and shell in nanospheres, nanocubes and octopodes due to a Fe1-xO@Fe3-xO4 coreshell structure45 whereas no contrast is observed in nanocubes after the oxidation step (Figure 1D). The structure and the composition of the nano-objects were determined through XRD analysis (Figure SI 1). XRD patterns were refined using Rietveld analysis (Figure SI 2). The XRD pattern of oxNC16 only showed the characteristic peaks of a single spinel iron oxide phase whereas those of NS19, NC16 and NO24 displayed the XRD peaks of both iron oxide spinel and wüstite phases (Figure SI 1). Indeed, it has already been shown45 that cubic NPs synthesized with the same procedure consist in NPs with a wüstite core and a spinel shell. The XRD patterns of NS19, NC16 and NO24 were refined considering two components ascribed to the spinel and wüstite phases respectively (Figure SI 2).

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Table 1. Lattice parameters of Fe1-xO and spinel phases in the different NPs deduced from Rietveld refinements. Lattice parameter (Å) Wüstite phase

Spinel phase

NS19

4.226(1)

8.401(2)

NC16

4.26(1)

8.429(5)

NO24

4.218 (3)

8.409(2)

4.283 (1)

oxNC16

X

8.378(2)

NS10

X

8.379(1)

For NO24, the best XRD refinements were only obtained by introducing two components for the wüstite phase with different cell parameters. It concurs with the presence of wüstite Fe1-xO with different oxidation states as already noticed with Fe1-xO @ Fe3-xO4 cubic shaped NPs 45 . However one may not exclude strains induced by the octopode morphology. The calculated cell parameters for each type of NPs are given in Table 1. For NS19, NC16 and NO24, the spinel lattice parameter is 8.401 (2), 8.429 (5) and 8.409 (2) respectively, which is slightly larger than that of bulk magnetite Fe3-xO4 (8.396 Å, JCPDS file 19-629). By contrast, the Fe1-xO core lattice parameter is smaller than the bulk value (4.326 Å, JCPDS file 01-89-687) of face-centered cubic (fcc) Fe1-xO (0.8 < 1-x 1 MHz) showing an agglomeration of the nanoparticles in agreement with the larger DLS size of these particles and the large r2/r1 ratio. The relaxivities of NC16 are low compared to those of their oxidized counterpart oxNC16 (Figures 7 and SI12a). Such results show the influence of a non magnetic Fe1-xO core. The experimental data were fitted using the usual model assuming a spherical shape of the particles.10,66 The Msat and radius fitted values as a function of the iron amount are shown in Table 5. The radius values agreed well with the TEM data for all particles and whatever the amount of iron considered. As expected, Msat of NS19, NC16 and NO24 increased when only the amount of iron corresponding to the magnetite phase is considered. For nanocubes, the r2 relaxivities increase with the magnetic field whereas for all other NPs, the values are similar at 60

and 300 MHz. The low values measured for NO24 may be related to low Msat. The size values obtained are the same for oxidized and non oxidized nanocubes but the saturation magnetization (Msat) was higher for OxNC16 (Table 5). This behavior agreed well with the largest amount of superparamagnetic material in oxNC16 as compared to NC16. The NMRD profile of NO24 is typical of large particles (> 20 nm) with some agglomerates. 100 NS10 NS19 NC16 NO24 oxNC16

80 -1

2.4.2. Nuclear magnetic resonance dispersion profiles

60

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relaxivity (s mM )

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40

20

0 0.01

0.1

1

10

100

1000

proton Larmor frequency (MHz)

Figure 7: NMRD profiles considering the amount of iron corresponding to the magnetite phase.

Both in vitro relaxivity measurements and NMRD profiles confirmed the very good in vitro MRI properties of core-shell (excluding octopodes) and cubic shape NPs. This might be related to the supplementary anisotropy introduced by the exchange bias properties and/or the cubic shape.

Table 5. Evolution of the NMRD radius and saturation magnetization (Msat) of the dendronized NPs considering the total amount of iron contained in each particles and considering the amount of iron stemming from the Fe3-xO4 phase.

Calculation considering the total amount of Fe Calculation considering the amount of Fe in Fe3-xO4 phase

NS10

NS19

NC16

NO24

oxNC16

Msat (Am /kg)

53.0 ± 0.3

32.0 ± 0.1

24.0 ± 0.1

18.9 ± 0.1

39.3 ± 0.7

radius (nm)

5.97 ± 0.04

7.90 ± 0.06

9.80 ± 0.05

10.0 ± 0.1

9.87 ± 0.03

Msat (Am /kg)

41.3 ± 0.2

32.3 ± 0.2

26.5 ± 0.1

39.3 ± 0.7

radius (nm)

7.72 ± 0.06

9.11 ± 0.05

10.1 ± 0.1

9.87 ± 0.03

2

2

2.4.3. In vivo MRI measurements Core-shell spherical NS19 were intravenous injected at an iron concentration of 1 µmol/kg which was a low concentration compared to usual concentrations injected in mice or rats (up to 50 µmol/kg of body weight) and in human (e.g. 7.5 µmol/kg for RESOVIST™). No macroscopic adverse effect was observed until 3 months after MRI exper-

iments; however any specific toxicological study was performed. The T2w MRI signal in different organs was followed as a function of time and is presented in Figure 8. After injection (at 3 min), no contrast change is evidenced in aorta, followed by a negative EHC which dramatically increases (-39% at 8min) and then stabilizes around at -19% during 10min. Such a strong T2w EHC decrease might be related to a clustering of NPs at the injection point and the fol-

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lowing evolution of the signal over time suggests a fragmentation of these aggregates upon blood circulation. A similar evolution of negative EHC is also observed in the kidney, cortex, pelvic and bladder and the observed values (-8 to -15 % at 14 min post-IV) demonstrate an urinary elimination of NPs. Urine sample removed at the end stage of MRI acquisition have been calcinated and TEM images have shown the presence NPs in the urine (Figure SI 13). The similar signal evolution in liver suggests that the liver signal was mainly due to blood circulation in this organ and that there is no reticulo endothelial system (RES) uptake. The T1w EHC depicted in Figure 8D evolved as expected over time except for blood. Indeed, the strong decrease after injection in blood is in agreement with and correlated to the strong negative contrast observed on T2w images (Figure 8B). These in vivo MRI results confirmed the in vitro study and allowed concluding that core–shell structures with a wüstite core and a magnetite shell could be used as MRI contrast agents even at low iron concentration. As good hyperthermia properties have also been noticed at low concentrations, these NPs appear promising for combining hyperthermia and MRI.

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the iron concentration decreased may be related to an aggregation of NPs at the injection followed by a fragmentation of aggregates upon blood circulation (- 9.5% at 8 min)(figure 9b). The comparison of the EHC evolution in blood between NS19 and oxNC16 suggests the formation of smaller aggregates with oxNC16. It decreased down to zero in the blood due to the decrease of NPs concentration in the blood related to the organs uptake. The evolution of the EHC in bladder suggests an urinary elimination. The signal in liver evolved similarly to that of blood with time suggesting that the liver signal was mainly due to blood circulation in this organ and that there is no RES uptake. These results suggest similar biokinetics between spherical core-shell NPs and oxidized nanocubes.

a)

In vivo studies were also conducted with dendronized oxidized nanocubes OxNC16 which displayed very interesting in vitro contrast properties. The T2w EHC in different organs as a function of time after IV (1.9 µmol/kg) of a low concentrated suspension are given in Figure 9.

Figure 9. A)T2w images centered on the kidneys (a0/a), aorta (bo/b), liver (co/c) and bladder (do/d) before/ and at the EHC peak after injection of oxNC16 at 1.9 µmol/kg equivalent iron concentration, and b) the generated curves of EHC(%) corresponding to each ROI ( Liver (Li)=, =Aorta (Ao), Right Cortex (RC), RPe= Right Pelvic, LK= Left Kidney).

Figure 8.A) T2w (A) and T1w (C) images centered on the liver and aorta (upper) and kidneys (lower), before (left) and at the peak signal (right) after injection of NS19 (right) with the Region of Interest (ROI) corresponding to the Liver (Li)=, =Aorta (Ao), Right Cortex (RC), RPe= Right Pelvic, LK= Left Kidney) and the generated curves of EHC(%) corresponding to each ROI on T2w (B) and T1w sequences.

As previously observed with NS19, the strong decrease of T2w EHC (-25 % at 6min30 vs -7 % at 1min30) although

The EHC evolution on T1w dynamic acquisition at low concentration (1.3 µmol/kg) in main organs is presented in Figure 10. A high positive contrast between 10 and 17 min post IV in the aorta (Figure 10) is observed while the signal is negative at the same times and conditions in the case of spherical core-shell NPs (Figure 8D). Such behavior may be related to the nanocubes ability to align in chains at low concentrations. Further studies are in progress to conclude on this hypothesis. To summarize, an inverse correlation between EHC enhancement and iron blood concentration was evidenced on dynamic T2w acquisition in the aorta after IV injection of core-shell NPs and oxidized nanocubes. The influence

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of the NPs clustering on the MRI properties has been reported by Roch et al. 67 during in vitro measurements at low magnetic field. They evidenced increased transverse relaxivity during the clustering process of iron oxide NPs up to a critical size and decreased relaxivity above this critical size. To investigate such clustering effect on in vivo MRI properties, suspensions at different iron concentration were injected. T1w and T2w signals were followed in different organs as a function of time delay after IV injection and as a function of the injected concentration. Only the T1w EHC and T2w EHC in blood (aorta) are presented on Figure 11.

tion may be related to the formation of aggregates of different sizes depending on the NPs concentration. At concentration higher than 2 µmol/kg, large aggregates are formed leading to high T2w negative contrast and low T1w positive contrasts. For concentration lower than 2 µMol/kg, smaller aggregates are probably formed leading to both high positive and negative contrasts. Whatever the concentrations: after 1 hour, the T2w signal slightly increases and reaches zero, proving the elimination of the NPs from the blood after 1 hour.

Figure 11.Generated EHC (%) curves of blood generated from aorta ROI drawn on T1w or T2w dynamic sequences as a function ofdifferent iron concentrations of oxNC16.

a)

3. CONCLUSION NPs with three different shapes (spherical, cubical and octopode shapes) displaying a wüstite core and a magnetite shell were synthesized and shown to display exchange bias properties (high exchange (He) and coercitive (Hc) fields) inducing an additional anisotropy. After an oxidation step, cubic nanoparticles with a composition close to a spinel iron oxide were obtained.

Figure 10. T1w images centered on the kidneys and aorta before (right) and at the EHC blood peak after injection of oxNC16 at 1.3 µmol/kg iron concentration, and the generated curves of EHC(%) corresponding to liver, aorta, cortex and pelvic area of each kidney. Arrows indicated the bright enhancement of signal generated in aorta and right pelvic after injection. For iron concentration smaller than 2 µmol/kg, a positive T1w EHC is observed as well as a negative T2w EHC. This suggested that for this range of concentration either T1w or T2w MRI can be performed. At higher concentration no more positive T1w EHC is observed and only a negative T2w EHC is noticed. This is in agreement with the results reported by Roch et al.59,60 demonstrating that the longitudinal relaxation rate enhancement decreases as the aggregate size increases. Thus the different contrast evolution in blood as function of the iron oxide concentra-

Hyperthermia measurements were performed on the most suitable nano-objects for MRI and demonstrated a dependence of the heating properties on iron concentration and a suitable heating power of core-shell and cubic shaped NPs at low concentration. Our extensive study of the MRI properties demonstrated that core-shell Fe1xO@Fe3-xO4 particles display very high in vitro as well as in vivo MRI properties, even at very low concentration. Thus, a spinel shell in core-shell nano-objects has been proved to be efficient as contrast agent. Furthermore oxidized nanocubes exhibit interesting positive T1w contrast at low concentration allowing envisioning a dual contrast agent (i.e. positive contrast on T1w images and negative contrast on T2w images) with an improvement of the sensitivity related to the bright signal and thus improving the safety of the imaging interpretation procedure. In this way, the nanostructures studied here appear very promising for combining MRI and hyperthermia.

AUTHOR INFORMATION Corresponding Author E-Mail : [email protected]

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E-Mail : [email protected] E-Mail : [email protected]

Author Contributions All authours contributed to writing the manuscript and approved the final version of the manuscript.

ACKNOWLEDGMENT This work was financially supported by the CNRS, the University of Strasbourg, the French Ministry of research (MENRT fellowship to A. Walter), the French National Research Agency (ANR) through NANOTHER and EMERGENT (fellowship to, A. Garofalo) projects. Thanks to Patrick Roux and Jean-Baptiste Langlois for their MRI technical assistance and Alain Derory for technical support with SQUID measurements. The authors thank also the CERMEP-Imagerie du Vivant (Bron, France) for the free access to 7T MRI equipment.

SUPPORTING INFORMATION AVAILABLE. Synthesis of the dendron molecule. Diffraction patterns of the particles. Magnetic measurements at 300K. Infrared spectroscopy. DLS measurements and supplementary MRI properties. This material is available free of charge via the Internet at http://pubs.acs.org. REFERENCES (1) Liong, M.; Lu, J.; Kovochich, M.; Xia, T.; Ruehm, S. G.; Nel, A. E.; Tamanoi, F.; Zink, J. I. ACS Nano 2008, 2, 889–896. (2) Kim, J.; Piao, Y.; Hyeon, T. Chem. Soc. Rev. 2009, 38, 372–390. (3) De, M.; Ghosh, P. S.; Rotello, V. M. Adv. Mater. 2008, 20, 4225–4241. (4) Mornet, S.; Vasseur, S.; Grasset, F.; Duguet, E. J. Mater. Chem. 2004, 14, 2161–2175. (5) Fang, C.; Zhang, M. J. Mater. Chem. 2009, 19, 6258– 6266. (6) Pankhurst, Q. A.; Connolly, J.; Jones, S. K.; Dobson, J. J. Phys. Appl. Phys. 2003, 36, R167. (7) Mura, S.; Couvreur, P. Adv. Drug Deliv. Rev. 2012, 64, 1394-14-16. (8) Choi, K. Y.; Liu, G.; Lee, S.; Chen, X. Nanoscale 2012, 4, 330–342. (9) Barick, K. C.; Singh, S.; Jadhav, N. V.; Bahadur, D.; Pandey, B. N.; Hassan, P. A. Adv. Funct. Mater. 2012, 22, 4975– 4984. (10) Laurent, S.; Forge, D.; Port, M.; Roch, A.; Robic, C.; Vander Elst, L.; Muller, R. N. Chem. Rev. 2008, 108, 2064–2110. (11) Na, H. B.; Song, I. C.; Hyeon, T. Adv. Mater. 2009, 21, 2133–2148. (12) Maier-Hauff, K.; Rothe, R.; Scholz, R.; Gneveckow, U.; Wust, P.; Thiesen, B.; Feussner, A.; Deimling, A.; Waldoefner, N.; Felix, R.; Jordan, A. J. Neurooncol. 2007, 81, 53–60. (13) Maier-Hauff, K.; Ulrich, F.; Nestler, D.; Niehoff, H.; Wust, P.; Thiesen, B.; Orawa, H.; Budach, V.; Jordan, A. J. Neurooncol. 2011, 103, 317–324. (14) Goya, G. F.; Asín, L.; Ibarra, M. R. Int. J. Hyperthermia 2013, 29, 810–818. (15) Gazeau, F.; Lévy, M.; Wilhelm, C. Nanomed. 2008, 3, 831–844.

Page 14 of 16

(16) Lee, J.-H.; Jang, J.; Choi, J.; Moon, S. H.; Noh, S.; Kim, J.; Kim, J.-G.; Kim, I.-S.; Park, K. I.; Cheon, J. Nat. Nanotechnol. 2011, 6, 418–422. (17) Guardia, P.; Di Corato, R.; Lartigue, L.; Wilhelm, C.; Espinosa, A.; Garcia-Hernandez, M.; Gazeau, F.; Manna, L.; Pellegrino, T. ACS Nano 2012, 6, 3080–3091. (18) Hugounenq, P.; Levy, M.; Alloyeau, D.; Lartigue, L.; Dubois, E.; Cabuil, V.; Ricolleau, C.; Roux, S.; Wilhelm, C.; Gazeau, F.; Bazzi, R. J. Phys. Chem. C 2012, 116, 15702–15712. (19) Reddy, L. H.; Arias, J. L.; Nicolas, J.; Couvreur, P. Chem. Rev. 2012, 112, 5818–5878. (20) Lu, A.-H.; Salabas, E. L.; Schüth, F. Angew. Chem. Int. Ed. 2007, 46, 1222–1244. (21) Yang, C.; Wu, J.; Hou, Y. Chem. Commun. 2011, 47, 5130–5141. (22) Park, J.; An, K.; Hwang, Y.; Park, J.-G.; Noh, H.-J.; Kim, J.-Y.; Park, J.-H.; Hwang, N.-M. Nat. Mater. 2004, 3, 891–895. (23) Sun, S.; Zeng, H.; Robinson, D. B.; Raoux, S.; Rice, P. M.; Wang, S. X.; Li, G. J Am Chem Soc 2003, 126, 273–279. (24) Smolensky, E. D.; Park, H.-Y. E.; Zhou, Y.; Marjanska, M.; Botta, M.; Pierre, V. J. Mater. Chem. B 2013. (25) De Montferrand, C.; Hu, L.; Milosevic, I.; Russier, V.; Bonnin, D.; Motte, L.; Brioude, A.; Lalatonne, Y. Acta Biomater. 2013, 9, 6150–6157. (26) Song, M.; Zhang, Y.; Hu, S.; Song, L.; Dong, J.; Chen, Z.; Gu, N. Colloids Surf. Physicochem. Eng. Asp. 2012, 408, 114–121. (27) Kucheryavy, P.; He, J.; John, V. T.; Maharjan, P.; Spinu, L.; Goloverda, G. Z.; Kolesnichenko, V. L. Langmuir 2013, 29, 710– 716. (28) Joshi, H. M.; Lin, Y. P.; Aslam, M.; Prasad, P. V.; Schultz-Sikma, E. A.; Edelman, R.; Meade, T.; Dravid, V. P. J Phys Chem C 2009, 113, 17761–17767. (29) Wang, W.; Pacheco, V.; Krause, H.-J.; Zhang, Y.; Dong, H.; Hartmann, R.; Willbold, D.; Offenhäusser, A.; Gu, Z. J. Phys. Chem. C 2012, 116, 17880–17884. (30) Lee, N.; Choi, Y.; Lee, Y.; Park, M.; Moon, W. K.; Choi, S. H.; Hyeon, T. Nano Lett. 2012, 12, 3127–3131. (31) Lee, N.; Kim, H.; Choi, S. H.; Park, M.; Kim, D.; Kim, H.-C.; Choi, Y.; Lin, S.; Kim, B. H.; Jung, H. S.; Kim, H.; Park, K. S.; Moon, W. K.; Hyeon, T. Proc. Natl. Acad. Sci. 2011, 108, 2662– 2667. (32) Lee, J.-H.; Huh, Y.-M.; Jun, Y.; Seo, J.; Jang, J.; Song, H.T.; Kim, S.; Cho, E.-J.; Yoon, H.-G.; Suh, J.-S.; Cheon, J. Nat. Med. 2006, 13, 95–99. (33) Cheong, S.; Ferguson, P.; Feindel, K. W.; Hermans, I. F.; Callaghan, P. T.; Meyer, C.; Slocombe, A.; Su, C.-H.; Cheng, F.-Y.; Yeh, C.-S.; Ingham, B.; Toney, M. F.; Tilley, R. D. Angew. Chem. Int. Ed. 2011, 50, 4206–4209. (34) Lacroix, L.-M.; Frey Huls, N.; Ho, D.; Sun, X.; Cheng, K.; Sun, S. Nano Lett. 2011, 11, 1641–1645. (35) Khurshid, H.; Hadjipanayis, C. G.; Chen, H.; Li, W.; Mao, H.; Machaidze, R.; Tzitzios, V.; Hadjipanayis, G. C. J. Magn. Magn. Mater. 2013, 331, 17–20. (36) Lee, N.; Hyeon, T. Chem. Soc. Rev. 2012, 41, 2575–2589. (37) Pöselt, E.; Kloust, H.; Tromsdorf, U.; Janschel, M.; Hahn, C.; Maßlo, C.; Weller, H. ACS Nano 2012, 6, 1619–1624. (38) Meiklejohn, W. H.; Bean, C. P. Phys. Rev. 1956, 102, 1413–1414. (39) Basly, B.; Popa, G.; Fleutot, S.; Pichon, B. P.; Garofalo, A.; Ghobril, C.; Billotey, C.; Berniard, A.; Bonazza, P.; Martinez, H.; Felder-Flesch, D.; Begin-Colin, S. Dalton Trans. 2012. (40) Basly, B.; Felder-Flesch, D.; Perriat, P.; Pourroy, G.; Bégin-Colin, S. Contrast Media Mol. Imaging 2011, 6, 132–138.

14


Page 15 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(41) Lamanna, G.; Kueny-Stotz, M.; Mamlouk-Chaouachi, H.; Ghobril, C.; Basly, B.; Bertin, A.; Miladi, I.; Billotey, C.; Pourroy, G.; Begin-Colin, S.; Felder-Flesch, D. Biomaterials 2011, 32, 8562–8573. (42) Ghobril, C.; Popa, G.; Parat, A.; Billotey, C.; Taleb, J.; Bonazza, P.; Begin-Colin, S.; Felder-Flesch, D. Chem. Commun. 2013, 49, 9158–9160. (43) Basly, B.; Felder-Flesch, D.; Perriat, P.; Billotey, C.; Taleb, J.; Pourroy, G.; Begin-Colin, S. Chem. Commun. 2010, 46, 985–987. (44) Thompson, P.; Cox, D. E.; Hastings, J. B. J. Appl. Crystallogr. 1987, 20, 79–83. (45) Pichon, B. P.; Gerber, O.; Lefevre, C.; Florea, I.; Fleutot, S.; Baaziz, W.; Pauly, M.; Ohlmann, M.; Ulhaq, C.; Ersen, O.; Pierron-Bohnes, V.; Panissod, P.; Drillon, M.; Begin-Colin, S. Chem Mater 2011, 23, 2886–2900. (46) Hai, H. T.; Yang, H. T.; Kura, H.; Hasegawa, D.; Ogata, Y.; Takahashi, M.; Ogawa, T. J. Colloid Interface Sci. 2010, 346, 37–42. (47) Wetterskog, E.; Tai, C.-W.; Grins, J.; Bergström, L.; Salazar-Alvarez, G. ACS Nano 2013, 7, 7132–7144. (48) Levy, M.; Quarta, A.; Espinosa, A.; Figuerola, A.; Wilhelm, C.; García-Hernández, M.; Genovese, A.; Falqui, A.; Alloyeau, D.; Buonsanti, R.; Cozzoli, P. D.; García, M. A.; Gazeau, F.; Pellegrino, T. Chem Mater 2011, 23, 4170–4180. (49) Hai, H. T.; Kura, H.; Takahashi, M.; Ogawa, T. J. Appl. Phys. 2010, 107, 09E301–09E301–3. (50) Kavich, D. W.; Dickerson, J. H.; Mahajan, S. V.; Hasan, S. A.; Park, J.-H. Phys. Rev. B 2008, 78, 174414. (51) Sun, X.; Frey Huls, N.; Sigdel, A.; Sun, S. Nano Lett. 2012, 12, 246–251. (52) Pan, B.; Cui, D.; Xu, P.; Ozkan, C.; Feng, G.; Ozkan, M.; Huang, T.; Chu, B.; Li, Q.; He, R.; Hu, G. Nanotechnology 2009, 20, 125101. (53) Pan, B.; Gao, F.; Gu, H. J. Colloid Interface Sci. 2005, 284, 1–6. (54) De la Presa, P.; Luengo, Y.; Multigner, M.; Costo, R.; Morales, M. P.; Rivero, G.; Hernando, A. J. Phys. Chem. C 2012, 116, 25602–25610. (55) Fortin, J.-P.; Wilhelm, C.; Servais, J.; Ménager, C.; Bacri, J.-C.; Gazeau, F. J Am Chem Soc 2007, 129, 2628–2635. (56) Lartigue, L.; Innocenti, C.; Kalaivani, T.; Awwad, A.; Sanchez Duque, M. del M.; Guari, Y.; Larionova, J.; Guérin, C.; Montero, J.-L. G.; Barragan-Montero, V.; Arosio, P.; Lascialfari, A.; Gatteschi, D.; Sangregorio, C. J Am Chem Soc 2011, 133, 10459– 10472. (57) Lévy, M.; Wilhelm, C.; Siaugue, J.-M.; Horner, O.; Bacri, J.-C.; Gazeau, F. J. Phys. Condens. Matter 2008, 20, 204133. (58) Bae, K. H.; Park, M.; Do, M. J.; Lee, N.; Ryu, J. H.; Kim, G. W.; Kim, C.; Park, T. G.; Hyeon, T. ACS Nano 2012, 6, 5266– 5273. (59) Martinez-Boubeta, C.; Simeonidis, K.; Makridis, A.; Angelakeris, M.; Iglesias, O.; Guardia, P.; Cabot, A.; Yedra, L.; Estradé, S.; Peiró, F.; Saghi, Z.; Midgley, P. A.; Conde-Leborán, I.; Serantes, D.; Baldomir, D. Sci. Rep. 2013, 3. (60) Mehdaoui, B.; Tan, R. P.; Meffre, A.; Carrey, J.; Lachaize, S.; Chaudret, B.; Respaud, M. Phys. Rev. B 2013, 87, 174419. (61) Lartigue, L.; Hugounenq, P.; Alloyeau, D.; Clarke, S. P.; Lévy, M.; Bacri, J.-C.; Bazzi, R.; Brougham, D. F.; Wilhelm, C.; Gazeau, F. ACS Nano 2012, 6, 10935–10949. (62) Serantes, D.; Simeonidis, K.; Angelakeris, M.; Chubykalo-Fesenko, O.; Marciello, M.; Morales, M. del P.; Baldomir, D.; Martinez-Boubeta, C. J. Phys. Chem. C 2014, 118, 5927–5934.

(63) Billotey, C.; Wilhelm, C.; Devaud, M.; Bacri, J. c.; Bittoun, J.; Gazeau, F. Magn. Reson. Med. 2003, 49, 646–654. (64) Paquet, C.; de Haan, H. W.; Leek, D. M.; Lin, H.-Y.; Xiang, B.; Tian, G.; Kell, A.; Simard, B. ACS Nano 2011, 5, 3104– 3112. (65) Basti, H.; Ben Tahar, L.; Smiri, L. S.; Herbst, F.; Vaulay, M.-J.; Chau, F.; Ammar, S.; Benderbous, S. J. Colloid Interface Sci. 2010, 341, 248–254. (66) Roch, A.; Gillis, P.; Ouakssim, A.; Muller, R. N. J. Magn. Magn. Mater. 1999, 201, 77–79. (67) Roch, A.; Gossuin, Y.; Muller, R. N.; Gillis, P. J. Magn. Magn. Mater. 2005, 293, 532–539.

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Mastering the Shape and Composition of Dendronized Iron Oxide

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