Saturation of Specific Absorption Rate for Soft and Hard Spinel Ferrite Nanoparticles Synthesized by Polyol Process

Spinel ferrite nanoparticles represent a class of magnetic nanoparticles (MNPs) with enormous potential in magnetic hyperthermia. In this study, we investigated the magnetic and heating properties of spinel soft NiFe2O4, MnFe2O4, and hard CoFe2O4 MNPs of comparable sizes (12–14 nm) synthesized by the polyol method. Similar to the hard ferrite, which predominantly is ferromagnetic at room temperature, the soft ferrite MNPs display a non-negligible coercivity (9–11 kA/m) arising from the strong interparticle interactions. The heating capabilities of ferrite MNPs were evaluated in aqueous media at concentrations between 4 and 1 mg/mL under alternating magnetic fields (AMF) amplitude from 5 to 65 kA/m at a constant frequency of 355 kHz. The hyperthermia data revealed that the SAR values deviate from the quadratic dependence on the AMF amplitude in all three cases in disagreement with the Linear Response Theory. Instead, the SAR values display a sigmoidal dependence on the AMF amplitude, with a maximum heating performance measured for the cobalt ferrites (1780 W/gFe+Co), followed by the manganese ferrites (835 W/gFe+Mn), while the nickel ferrites (540 W/gFe+Ni) present the lowest values of SAR. The heating performances of the ferrites are in agreement with their values of coercivity and saturation magnetization

Spin-dependent tunneling into single cobalt-phthalocyanine molecules

Cette thèse présente une étude des propriétés électroniques polarisés en spin d'une molécule individuélle de cobalt-phthalocyanine (CoPc), qui sont potentiellement intéressantes pour le domaine émergeant de l'électronique de spin. Les résultats expérimentThe thesis presents an experimental study of both the electronic and the spin-polarized properties of single cobalt-phthalocyanine (CoPc) molecules, which are potentially interesting for the emerging eld of molecular spintronics. The CoPc molecules were

Spin-dependent tunneling into single cobalt-phthalocyanine molecules

Cette thèse présente une étude des propriétés électroniques polarisés en spin d'une molécule individuélle de cobalt-phthalocyanine (CoPc), qui sont potentiellement intéressantes pour le domaine émergeant de l'électronique de spin. Les résultats expérimentaux sont analysés par des calculs de type DFT en collaborartion avec J. Kortus (Université Technique de Freiberg, Allemagne). Les molécules de CoPc ont été déposés sur des surfaces non-magnétiques et magnétiques, pour ensuite être individuellement étudiés à basse température par un microscope à effet tunnel. Deux aspects fondamentaux sont abordés: l'injection d'électrons polarisés en spin dans une molécule individuelle et le couplage magnétique de cette molécule avec une surface magnétique. En utilisant une pointe de Co polarisée en spin et un nanoîlot des Co comme électrodes magnétiques et la molécule de CoPc comme élément actif, une résonance polarisée en spin est identiée sur le centre de la molécule. Cette résonance, ayant pour origine les orbitals moléculaire d'du cobalt, reète l'existence d'états stationnaires des spin. Ces états prouvent notamment que le moment magnetique de CoPc est figé dans une direction " up " ou " down " après adsorption sur la surface de cobalt magnétique. Les calculs DFT montrent que la molécule de CoPc est ferromagnétiquement couplée avec les nanoîlots via deux mécanismes d'échange (direct et superéchange) et illustrent le rôle important joué par les ligands organiques dans le magnétisme mais aussi dans le transport de spin. Des études expérimentales comparatives ont été effectué sur des surfaces non-magnétiques [Au(111) et Cu(111)] où la molécule de CoPc devient non-magnétique après adsorption comme les calculs DFT le prédisent.The thesis presents an experimental study of both the electronic and the spin-polarized properties of single cobalt-phthalocyanine (CoPc) molecules, which are potentially interesting for the emerging eld of molecular spintronics. The CoPc molecules were deposited on a nonmagnetic and a magnetic surface and individually studied at low temperature using a scanning tunneling microscope. Two fundamental aspects of molecular spintronics are addressed, namely the injection of electron spins into a single molecule and the magnetic coupling of the molecule with the underlying magnetic surface. To do so, spin-polarized scanning tunneling spectroscopy is employed to locally inject spin-polarized electron across the vacuum barrier into a single CoPc molecule. Using the spin-polarized Co terminated tip and Co nanoislands of opposite magnetization as magnetic electrodes, and the CoPc molecule as an active element, spin-polarized electronic features are identied over the center of the molecule. The Co nanoislands were grown on Cu(111) and thoroughly calibrated to eliminate electronic artifacts. The stationary spin states of CoPc arise from the d-orbitals of the cobalt ion and reect two molecular spin orientations. DFT calculations establish that CoPc couples ferromagnetically with the Co nanoislands through two exchange mechanisms (direct and superexchange), illustrating the important role played by the organic ligands in the spin-dependent transport properties. Comparative experimental studies are done on non-magnetic surfaces [Au(111) and Cu(111)], where the paramagnetic CoPc becomes non-magnetic upon adsorption, as DFT calculations predict

Visualisation de la polarisation en spin d'une molécule par microscopie à effet tunnel

Cette thèse présente une étude des propriétés électroniques polarisés en spin d'une molécule individuélle de cobalt-phthalocyanine (CoPc), qui sont potentiellement intéressantes pour le domaine émergeant de l'électronique de spin. Les résultats expérimentaux sont analysés par des calculs de type DFT en collaborartion avec J. Kortus (Université Technique de Freiberg, Allemagne). Les molécules de CoPc ont été déposés sur des surfaces non-magnétiques et magnétiques, pour ensuite être individuellement étudiés à basse température par un microscope à effet tunnel. Deux aspects fondamentaux sont abordés: l'injection d'électrons polarisés en spin dans une molécule individuelle et le couplage magnétique de cette molécule avec une surface magnétique. En utilisant une pointe de Co polarisée en spin et un nanoîlot des Co comme électrodes magnétiques et la molécule de CoPc comme élément actif, une résonance polarisée en spin est identiée sur le centre de la molécule. Cette résonance, ayant pour origine les orbitals moléculaire d du cobalt, reète l'existence d'états stationnaires des spin. Ces états prouvent notamment que le moment magnetique de CoPc est figé dans une direction " up " ou " down " après adsorption sur la surface de cobalt magnétique. Les calculs DFT montrent que la molécule de CoPc est ferromagnétiquement couplée avec les nanoîlots via deux mécanismes d'échange (direct et superéchange) et illustrent le rôle important joué par les ligands organiques dans le magnétisme mais aussi dans le transport de spin. Des études expérimentales comparatives ont été effectué sur des surfaces non-magnétiques [Au(111) et Cu(111)] où la molécule de CoPc devient non-magnétique après adsorption comme les calculs DFT le prédisent.The thesis presents an experimental study of both the electronic and the spin-polarized properties of single cobalt-phthalocyanine (CoPc) molecules, which are potentially interesting for the emerging eld of molecular spintronics. The CoPc molecules were deposited on a nonmagnetic and a magnetic surface and individually studied at low temperature using a scanning tunneling microscope. Two fundamental aspects of molecular spintronics are addressed, namely the injection of electron spins into a single molecule and the magnetic coupling of the molecule with the underlying magnetic surface. To do so, spin-polarized scanning tunneling spectroscopy is employed to locally inject spin-polarized electron across the vacuum barrier into a single CoPc molecule. Using the spin-polarized Co terminated tip and Co nanoislands of opposite magnetization as magnetic electrodes, and the CoPc molecule as an active element, spin-polarized electronic features are identied over the center of the molecule. The Co nanoislands were grown on Cu(111) and thoroughly calibrated to eliminate electronic artifacts. The stationary spin states of CoPc arise from the d-orbitals of the cobalt ion and reect two molecular spin orientations. DFT calculations establish that CoPc couples ferromagnetically with the Co nanoislands through two exchange mechanisms (direct and superexchange), illustrating the important role played by the organic ligands in the spin-dependent transport properties. Comparative experimental studies are done on non-magnetic surfaces [Au(111) and Cu(111)], where the paramagnetic CoPc becomes non-magnetic upon adsorption, as DFT calculations predict.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Enhanced Magnetic Hyperthermia Performance of Zinc Ferrite Nanoparticles under a Parallel and a Transverse Bias DC Magnetic Field

The collective organization of magnetic nanoparticles (MNPs) influences significantly their hyperthermic properties, relevant for their in vitro and in vivo applications. We report a systematic investigation of the effects of the concentration and the static bias direct current (DC) magnetic field superposed over the alternating magnetic field (AMF), both in a parallel and perpendicular configuration, on the specific absorption rate (SAR) by using zinc ferrite MNPs. The nonmonotonic dependence of the SAR on the concentration, with a maximum at very small concentrations (c ≤ 0.1 mgFe/mL), followed by a minimum at 0.25 mgFe/mL, and the second maximum of 3.3 kW/gFe at around 1 mgFe/mL, was explained by the passage of the MNPs from a single particle behavior to a collective one and the role of the dipolar interactions. By superposing a static 10 kA/m bias DC field on the AMF we obtained an increase in the SAR for both parallel and perpendicular orientations, up to 4285 W/gFe and 4070 W/gFe, respectively. To the best of our knowledge, this is the first experimental proof of a significant enhancement of the SAR produced by a perpendicular DC field. The effect of the DC field to increase the SAR is accompanied by an increase in the hyperthermia coercive field (HcHyp) for both configurations. No enhancement of the DC fields was noticed for the MNPs immobilized in a solid matrix but the DC field increases the HcHyp only in the parallel configuration. This translates into a higher SAR value for the perpendicular configuration as compared to the parallel configuration. These results have practical applications for magnetic hyperthermia

Doxorubicin Loaded Thermosensitive Magneto-Liposomes Obtained by a Gel Hydration Technique: Characterization and In Vitro Magneto-Chemotherapeutic Effect Assessment

The combination of magnetic hyperthermia with chemotherapy is considered a promising strategy in cancer therapy due to the synergy between the high temperatures and the chemotherapeutic effects, which can be further developed for targeted and remote-controlled drug release. In this paper we report a simple, rapid, and reproducible method for the preparation of thermosensitive magnetoliposomes (TsMLs) loaded with doxorubicin (DOX), consisting of a lipidic gel formation from a previously obtained water-in-oil microemulsion with fine aqueous droplets containing magnetic nanoparticles (MNPs) dispersed in an organic solution of thermosensitive lipids (transition temperature of ~43 °C), followed by the gel hydration with an aqueous solution of DOX. The obtained thermosensitive magnetoliposomes (TsMLs) were around 300 nm in diameter and exhibited 40% DOX incorporation efficiency. The most suitable MNPs to incorporate into the liposomal aqueous lumen were Zn ferrites, with a very low coercive field at 300 K (7 kA/m) close to the superparamagnetic regime, exhibiting a maximum absorption rate (SAR) of 1130 W/gFe when dispersed in water and 635 W/gFe when confined inside TsMLs. No toxicity of Zn ferrite MNPs or of TsMLs was noticed against the A459 cancer cell line after 48 h incubation over the tested concentration range. The passive release of DOX from the TsMLs after 48h incubation induced a toxicity starting with a dosage level of 62.5 ug/cm2. Below this threshold, the subsequent exposure to an alternating magnetic field (20–30 kA/m, 355 kHz) for 30 min drastically reduced the viability of the A459 cells due to the release of incorporated DOX. Our results strongly suggest that TsMLs represent a viable strategy for anticancer therapies using the magnetic field-controlled release of DOX

Assembly of 2D ionic layers by reaction of alkali halides with the organic electrophile 7,7,8,8-tetracyano-p-quinodimethane (TCNQ)

Sublimation of alkali halides (NaCl and LiCl) onto a pre-assembled hydrogen-bonded layer of TCNQ on Au(111) resulted in the formation of 2D ionic layers via a direct charge-transfer reaction without involvement of the substrate. The presented approach allows for the fabrication of different ionic layers, decoupled from the substrate and offering new, potentially interesting properties

One-Step Synthesis of PEGylated Gold Nanoparticles with Tunable Surface Charge

The present work reports a rapid, simple and efficient one-step synthesis and detailed characterisation of stable aqueous colloids of gold nanoparticles (AuNPs) coated with unmodified poly(ethylene)glycol (PEG) molecules of different molecular weights and surface charges. By mixing and heating aqueous solutions of PEG with variable molecular chain and gold(III) chloride hydrate (HAuCl4) in the presence of NaOH, we have successfully produced uniform colloidal 5 nm PEG coated AuNPs of spherical shape with tunable surface charge and an average diameter of 30 nm within a few minutes. It has been found out that PEGylated AuNPs provide optical enhancement of the characteristic vibrational bands of PEG molecules attached to the gold surface when they are excited with both visible (532 nm) and NIR (785 nm) laser lines. The surface enhanced Raman scattering (SERS) signal does not depend on the length of the PEG molecular chain enveloping the AuNPs, and the stability of the colloid is not affected by the addition of concentrated salt solution (0.1 M NaCl), thus suggesting their potential use for in vitro and in vivo applications. Moreover, by gradually changing the chain length of the biopolymer, we were able to control nanoparticles’ surface charge from −28 to −2 mV, without any modification of the Raman enhancement properties and of the colloidal stability

Controlling the Dimensionality and Structure of Supramolecular Porphyrin Assemblies by their Functional Substituents: Dimers, Chains, and Close-Packed 2D Assemblies

A staging of supramolecular aggregation from (0D) clusters to (1D) chains and (2D) assemblies as a function of molecular coverage of dipolar porphyrins adsorbed on the Ag(111) surface is described. It displays a complex interplay of both attractive and repulsive molecule–molecule interactions, the emergence of chirality, and the registry of the substrate.