Geneviève Pourroy

Nanoparticles for Imaging, Sensing, and Therapeutic Intervention

Nanoparticles have the potential to contribute to new modalities in molecular imaging and sensing as well as in therapeutic interventions. In this Nano Focus article, we identify some of the current challenges and knowledge gaps that need to be confronted to accelerate the developments of various applications. Using specific examples, we journey from the characterization of these complex hybrid nanomaterials; continue with surface design and (bio)physicochemical properties, their fate in biological media and cells, and their potential for cancer treatment; and finally reflect on the role of animal models to predict their behavior in humans.

Dendronized iron oxide nanoparticles for multimodal imaging

The synthesis of small-size dendrons and their grafting at the surface of iron oxide nanoparticles were achieved with the double objective to obtain a good colloidal stability with a mean hydrodynamic diameter smaller than 100 nm and to ensure the possibility of tuning the organic coating characteristics including morphology, functionalities, physico-chemical properties, grafting of fluorescent or targeting molecules. Magnetic resonance and fluorescence imaging are then demonstrated to be simultaneously possible using such versatile superparamagnetic iron oxide nanocrystals covered by a dendritic shell displaying either carboxylate or ammonium groups at their periphery which could be further labelled with a fluorescent dye. The grafting conditions of these functionalized dendrons at the surface of SPIO NPs synthesized by co-precipitation have been optimized as a function of the nature of the peripheral functional group. The colloidal stability has been investigated in water and osmolar media, and in vitro and in vivo MRI and optical imaging measurements have been performed showing encouraging biodistribution.

Properties and suspension stability of dendronized iron oxide nanoparticles for MRI applications

Functionalized iron oxide nanoparticles have attracted an increasing interest in the last 10 years as contrast agents for MRI. One challenge is to obtain homogeneous and stable aqueous suspensions of iron oxide nanoparticles without aggregates. Iron oxide nanoparticles with sizes around 10 nm were synthesized by two methods: the particle size distribution in water suspension of iron oxide nanoparticles synthesized by the co-precipitation method was improved by a process involving two steps of ligand exchange and phase transfer and was compared with that of iron oxide nanoparticles synthesized by thermal decomposition and functionalized by the same dendritic molecule. The saturation magnetization of dendronized nanoparticles synthesized by thermal decomposition was lower than that of nanoparticles synthesized by co-precipitation. The r(2) relaxivity values were shown to decrease with the agglomeration state in suspension and high r(2) values and r(2) /r(1) ratios were obtained with nanoparticles synthesized by co-precipitation by comparison with those of commercial products. Dendronized iron oxide nanoparticles thus have potential properties as contrast agent.

Epitaxial thin films of multiferroic GaFeO3 on conducting indium tin oxide (001) buffered yttrium-stabilized zirconia (001) by pulsed laser deposition

Epitaxial films of an alternative multiferroic material, GaFeO3 (GFO), were grown by pulsed laser deposition on yttrium-stabilized zirconia (001) and on conducting buffer layers of indium tin oxide (001). They present a perfect epitaxial growth along the GFO [010] axis and six crystallographic variants in the film’s plane. Their magnetic properties are close to those of the bulk with an out-of-plane [010] hard direction and a Curie temperature of ∼200K. The films did exhibit ferroelectric properties when characterized by electrostatic force microscopy.

Room temperature ferrimagnetic thin films of the magnetoelectric Ga2−xFexO3

(0k0) oriented films of the magnetoelectric material Ga2−xFexO3 (0.8 ≤ x ≤ 1.4) have been grown by pulsed laser deposition on various substrates: the non conducting yttrium stabilized zirconia (YSZ) (001) and the conducting indium tin oxide (ITO) buffered YSZ(001) and single crystalline Pt(111) buffered YSZ(111). The films are ferrimagnetic for all compositions and their Curie temperature increases with x. For x = 1.4, their Curie temperature is above room temperature (370 K) and their room temperature saturation magnetization is 90 emu/cm3. The effect of the conducting substrates on both the crystalline and electrical properties of the films has been studied. The single crystalline Pt(111) buffered YSZ(111) substrates allow substantial improvements both on the crystallographic and electrical points of view with a reduction of the number of in-plane variants down to 3 and a decrease of the leakage current down to 10−5 A at 10 V. This work opens new perspectives for the integration of a room temperature ferrimagnetic magnetoelectric material in spintronic devices.

Structural defects in Sr2FeMoO6 double perovskite: Experimental versus theoretical approach

The lower than expected magnetization of imperfect Sr2FeMoO6 (SFMO) double perovskites is usually attributed to the presence of Fe at antisite positions that would be antiferromagnetically coupled to their regular neighbors. However, ab initio calculations suggest strongly that such defective Fe sites would be ferromagnetically coupled and, consequently, the magnetization reduction would originate from other kinds of defects. The magnetic, hyperfine, and structural properties of SFMO perovskites prepared by solid-state reaction under a variety of conditions are reported and correlated with ab initio calculations of the magnetic moments and hyperfine fields of Mo and Fe ions in different local environments (antisites, antisite neighbors, and neighbors of an oxygen vacancy). When plotted against the order parameter the experimental magnetization is found to decrease at a rate of about −7.6μB per Mo–Fe antisite pair as in other previous experiments, where the theoretical calculation predicts −6.56μB per anti...

Effect of ball-milling and Fe-/Al-doping on the structural aspect and visible light photocatalytic activity of TiO2 towards Escherichia coli bacteria abatement.

Escherichia coli abatement was studied in liquid phase under visible light in the presence of two commercial titania photocatalysts, and of Fe- and Al-doped titania samples prepared by high energy ball-milling. The two commercial titania photocatalysts, Aeroxide P25 (Evonik industries) exhibiting both rutile and anatase structures and MPT625 (Ishihara Sangyo Kaisha), a Fe-, Al-, P- and S-doped titania exhibiting only the rutile phase, are active suggesting that neither the structure nor the doping is the driving parameter. Although the MPT625 UV-visible spectrum is shifted towards the visible domain with respect to the P25 one, the effect on bacteria is not increased. On the other hand, the ball milled iron-doped P25 samples exhibit low activities in bacteria abatement under visible light due to charge recombinations unfavorable to catalysis as shown by photoluminescence measurements. While doping elements are in interstitial positions within the rutile structure in MPT625 sample, they are located at the surface in ball milled samples and in isolated octahedral units according to (57)Fe Mössbauer spectrometry. The location of doping elements at the surface is suggested to be responsible for the sample cytotoxicity observed in the dark.

Fluoride controlled release tablets for intrabuccal use.

We have developed a fluoride controlled release delivering system for intrabuccal use, permitting to reach high enough local concentrations for desirable therapeutic effect with minimal side effects. We have formulated tablets of 160-200mg intended to be fixed on a tooth. The tablets have a granular matrix composed of pure hydroxyapatite, Eudragit((R)) and/or ethylcellulose. NaF is added either by a mechanical mixing or an impregnation method. Profiles of continuous in vitro drug release in saline phosphate buffered solution were recorded by means of a fluoride selective electrode. Linear profiles are observed when ethylcellulose is used. The most reproducible results are obtained when the impregnation method is used. Eudragit((R)) increases the dissolution efficiencies while ethylcellulose decreases it.

Pressure effect on the magnetization of Sr2FeMoO6 thin films grown by pulsed laser deposition

Thin films of Sr2FeMoO6 (SFMO) are grown on SrTiO3 (001) substrates by pulsed laser deposition. The best films provide 3.2μB∕f.u. at 5K, a Curie temperature above 400K, low roughness, high crystallinity, and low splashing. Therefore, the use of such SFMO electrodes in magnetic tunnel junctions patterned with conventional lithography is promising. Pseudomorphic epitaxial growth is obtained for thicknesses under 50nm. Above this thickness the films do not relax homogeneously. A coherent and systematic variation of the magnetization with the deposition conditions is obtained, which highlights a high reproducibility. Under a reasonable O2 partial pressure to avoid parasite phases, the limiting factor for high magnetization is the total pressure or the deposition rate. Therefore, the deposition rate is suspected to have a strong influence on the Fe∕Mo ordering. Highly magnetic samples are obtained under a low gas flow of either a 20% O2+N2 or a 0.3% O2+Ar.

Stabilization of iron-cobalt alloy isomorphous of α-Mn in a metal ferrite composite

Abstract An iron-cobalt alloy isomorphous with α-Mn and containing 28 at.% Fe is observed in the metal-oxide composite synthesized in aqueous media below 130 °C. The oxide is a cobalt-containing magnetite. The metal has two structures: the α-Mn, also called Re24Ti5, structure (space group I − 43m) with a = 8.747(1) A , and a b.c.c. (α-Fe) structure with a = 2.842(1) A . The powder pattern has been refined by using a Rietveld method. The α-Mn structure transforms into the b.c.c. structure above 170 °C.