Francesco Pineider - Academia.edu (original) (raw)
Papers by Francesco Pineider
Nature, 2010
A fundamental step towards atomic-or molecular-scale spintronic devices has recently been made by... more A fundamental step towards atomic-or molecular-scale spintronic devices has recently been made by demonstrating that the spin of an individual atom deposited on a surface 1 , or of a small paramagnetic molecule embedded in a nanojunction 2 , can be externally controlled. An appealing next step is the extension of such a capability to the field of information storage, by taking advantage of the magnetic bistability and rich quantum behaviour of single-molecule magnets 3-6 (SMMs). Recently, a proof of concept that the magnetic memory effect is retained when SMMs are chemically anchored to a metallic surface 7 was provided. However, control of the nanoscale organization of these complex systems is required for SMMs to be integrated into molecular spintronic devices 8,9 . Here we show that a preferential orientation of Fe 4 complexes on a gold surface can be achieved by chemical tailoring. As a result, the most striking quantum feature of SMMs-their stepped hysteresis loop, which results from resonant quantum tunnelling of the magnetization 5,6 -can be clearly detected using synchrotron-based spectroscopic techniques. With the aid of multiple theoretical approaches, we relate the angular dependence of the quantum tunnelling resonances to the adsorption geometry, and demonstrate that molecules predominantly lie with their easy axes close to the surface normal. Our findings prove that the quantum spin dynamics can be observed in SMMs chemically grafted to surfaces, and offer a tool to reveal the organization of matter at the nanoscale.
Magneto-optical (MO) techniques are well-established procedures to characterize the dynamics and ... more Magneto-optical (MO) techniques are well-established procedures to characterize the dynamics and reversal process of nanostructured materials and surfaces. At the same time MO properties include information on the band structure because MO effects are produced by the spin-orbit coupling. This interaction is largely modified in nanomaterials due to quantum confinement effects, changes in the electronic structure and surface contribution. Electronic plasmon excitations, typical of metal nanostructures, can also affect the MO response and the magnetic dynamics. Moreover the interaction between femtosecond light and magnetic materials can produce changes in the dynamic of the reversal process. As a consequence MO studies are emerging as fundamental methods to investigate the correlations between the magnetic, optical and electronic properties of nano-sized materials with an important role for understanding the possibility of manipulation of the magnetic information with light. In our pr...
Page 1. XMCD FOR THE INVESTIGATION OF SINGLE MOLECULE MAGNETS BASED SELF-ASSEMBLED MONOLAYERS Mat... more Page 1. XMCD FOR THE INVESTIGATION OF SINGLE MOLECULE MAGNETS BASED SELF-ASSEMBLED MONOLAYERS Matteo MANNINI,a Philippe SAINCTAVIT,b Chiara DANIELI,c Francesco PINEIDER,a Christophe CARTIER ...
ABSTRACT A detailed study of the composition and structure of Co-doped maghemite nanoparticles wi... more ABSTRACT A detailed study of the composition and structure of Co-doped maghemite nanoparticles with systematically varying composition has been carried out by Transmission Electron Microscopy (TEM) techniques, such as high resolution TEM (HRTEM), scanning TEM (STEM) and Energy Dispersive X-ray Spectrometry (EDS), and by X-ray absorption spectroscopy (XAS) at the Fe and Co K-edges, analyzing both the Extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near edge structure (XANES) regions. The latter techniques in particular, allow us to determine the degree of inversion of divalent and trivalent metal ions among the octahedral and tetrahedral sites in the spinel structure of the nanoparticles and gives detailed information on atomic distances. The samples consist of single-crystal nanoparticles with a composition corresponding to the Fe/Co ratio used in the synthesis. The degree of inversion is quite similar for all samples and close to the value found in a pure cobalt ferrite bulk sample.
We present the magnetic, optical and relaxometric properties of multifunctional Au-Fe 3 O 4 hybri... more We present the magnetic, optical and relaxometric properties of multifunctional Au-Fe 3 O 4 hybrid nanoparticles (HNPs), as possible novel contrast agents (CAs) for magnetic resonance imaging (MRI). The HNPs have been synthesized by wet chemical methods in heterodimer and core-shell geometries and capped with oleylamine. Structural characterization of the samples have been made by X-ray diffraction and transmission electron microscopy, while magnetic properties have been investigated by means of Superconducting Quantum Interference Device-SQUID magnetometry experiments. As required for MRI applications using negative CAs, the samples resulted superparamagnetic at room temperature and well above their blocking temperatures. Optical properties have been investigated by analyzing the optical absorbtion spectra collected in UV-visible region. Relaxometric measurements have been performed on organic suspensions of HNPs and Nuclear Magnetic Resonance (NMR) dispersion curves have been obtained by measuring the longitudinal 1/T 1 and transverse 1/T 2 relaxation rates of solvent protons in the range 10 kHz/300 MHz at room temperature. NMR relaxivities r 1 and r 2 have been compared with ENDOREM s , one of the commercial superparamagnetic iron oxide based MRI contrast agents. MRI contrast enhancement efficiencies have been investigated also by examining T 2 -weighted MR images of suspensions. The experimental results suggest that the nanoparticles' suspensions are good candidates as negative CAs.
The Journal of Physical Chemistry C, 2015
We report a broadband 1 H NMR study of the spin dynamics of coated maghemite and gold−maghemite h... more We report a broadband 1 H NMR study of the spin dynamics of coated maghemite and gold−maghemite hybrid nanostructures with two different geometries, namely dimers and core−shells. All the samples have a superparamagnetic behavior, displaying a blocking temperature (T B ∼ 80 K (maghemite), ∼105 K (dimer), ∼150 K (core−shell)), and the magnetization reversal time follows the Vogel−Fulcher law. We observed three different anomalies in 1 H NMR T 1 −1 versus T that decrease in amplitude when increasing the applied magnetic field. We suggest that the anomalies are related to three distinct system dynamics: molecular rotations of the organic groups (240 < T < 270 K), superparamagnetic spin blockage (100 < T < 150 K), and surface−core spin dynamics (T < 25 K). By fitting the T 1 −1 data with a heuristic model, we achieved a good agreement with magnetic relaxation data and literature values for methyl group rotation frequencies.
Journal of Materials Chemistry C, 2013
ABSTRACT Terbium(III) bis-phthalocyaninato neutral complex, a robust and evaporable Single Molecu... more ABSTRACT Terbium(III) bis-phthalocyaninato neutral complex, a robust and evaporable Single Molecule Magnet (SMM) with a record height of the anisotropy barrier, has recently attracted a great interest as an active unit in single molecule electronics, but at the same time its magnetic hysteresis has been found to be strongly affected when the environment is different from the crystalline phase. Here we present a systematic investigation of the magnetization dynamics in different environments, obtained by magnetic dilution, thermal treatment and sublimation of the molecules, to shed some light on the origin of the evanescence of the hysteretic behavior of this unique SMM.
Springer Proceedings in Physics, 2010
Molecular magnetism is here presented with emphasis concerning the single molecule magnets (SMMs)... more Molecular magnetism is here presented with emphasis concerning the single molecule magnets (SMMs). The architecture of SMMs is reviewed as well as the various ingredients promoting magnetic anisotropy and the relation between magnetic anisotropy and the dynamics of magnetization. Then it is shown how XAS and XMCD can be unique tools to unravel the magnetic properties of SMM submonolayers grafted on clean surfaces. We bring a special attention to the spectral features associated with the magnetic anisotropy and magnetization dynamics.
Chemistry of Materials, 2015
ABSTRACT In iron oxide nanoparticles the transformation of the metastable magnetite phase to magh... more ABSTRACT In iron oxide nanoparticles the transformation of the metastable magnetite phase to maghemite, through the oxidation of iron, often represents a major drawback for correct interpretation of their physical properties and their effective use in several applicative areas. To solve this issue we propose an innovative method for identifying the chemical composition of complex ferrite nanostructures based on magneto-optical (MO) spectroscopy. Spherical iron oxide nanoparticles with increasing size are investigated by magnetic circular dichroism (MCD) in the nUV-vis-nIR range (350-1000 nm). Particular attention is dedicated to the time evolution of the MO response, which is ascribable to the oxidation process of the nanomaterial. The measured MCD spectra show a complex line shape due to the overlap of several MO transitions. Deconvolution analysis of MCD hysteresis loops allows the interpretation of this complex response as the combination of two distinct contributions, originating from magnetite and maghemite domains in the nanoparticles. We consider this method a viable complement to conventional techniques for the discrimination of the two magnetic phases in nanostructured materials.
Nano Letters, 2014
Advanced nanostructured materials, such as gold nanoparticles, magnetic nanoparticles, and multif... more Advanced nanostructured materials, such as gold nanoparticles, magnetic nanoparticles, and multifunctional materials, are nowadays used in many state-of-the-art biomedical application. However, although the engineering in this field is very advanced, there remain some fundamental problems involving the interaction mechanisms between nanostructures and cells or tissues. Here we show the potential of 1 H NMR in the investigation of the uptake of two different kinds of nanostructures, that is, maghemite and gold nanoparticles, and of a chemotherapy drug (Temozolomide) in glioblastoma tumor cells. The proposed experimental protocol provides a new way to investigate the general problem of cellular uptake for a variety of biocompatible nanostructures and drugs.
The Journal of Physical Chemistry C, 2012
ABSTRACT We present a study of the structural, magnetic, and magneto-optical properties of a seri... more ABSTRACT We present a study of the structural, magnetic, and magneto-optical properties of a series of Co-substituted ferrite nanoparticles (NPs) prepared by thermal decomposition of metallo-organic precursors in high boiling solvents. The structural characterization, carried out by using several techniques (transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and magnetic circular dichroism measurements), showed all the samples are high crystalline, 5–6 nm spherical NPs with the cubic spinel structure typical of ferrites. The evolution of lattice parameters with cobalt content suggests that the material is Co-substituted maghemite, also confirmed by XAS and magneto optical (MO) characterizations. The investigation of the magnetic and magneto-optical properties displays peculiar trends with the cobalt content, the main features being the large increase of the saturation magnetization and the anomalous dependence of magnetic anisotropy which reaches its maximum values for intermediate compositions. The large tuneability of this material makes it possible to implement the performances of devices used in biomedical and sensing applications.
Soft Matter, 2011
The paper describes the effect of a low-frequency alternating magnetic field (LF-AMF) on the perm... more The paper describes the effect of a low-frequency alternating magnetic field (LF-AMF) on the permeability and release properties of large (LUVs) and giant (GUVs) unilamellar vesicles loaded with citrate coated cobalt ferrite nanoparticles (NPs). The citrate shell allows a high loading of NPs in lipid vesicles without modifying their magnetic properties. The increase of magnetic LUVs permeability upon exposure to LF-AMF has been evaluated as the fluorescence self-quenching of carboxyfluorescein (CF) entrapped inside the liposome aqueous pool. Liposome leakage has been monitored as a function of field frequency, time exposure and concentration of the citrate coated NPs. Confocal Laser Scanning Microscopy (CLSM) experiments performed on magnetic GUVs labeled with the fluorescent probe DiIC 18 and loaded with Alexa 488-C5-maleimide fluorescent dye provided insights on the release mechanism induced by LF-AMF. The results show that LF-AMF strongly affects vesicles permeability, suggesting the formation of pores in the lipid bilayer due to both hyperthermic effects and nanoparticle oscillations in the vesicles pool at the applied frequency. The behaviour of these magnetic vesicles in the presence of LF-AMF makes this system a good candidate for controlled drug delivery. † Electronic supplementary information (ESI) available: Cryo-TEM images of magnetoliposomes, AC-measurements on powder samples of citrate-coated and uncoated Cobalt ferrite nanoparticles, picture of the magnet used to apply the LF-AMF, measurements of the magnetic field anisotropy of the magnet at different positions. See
Optics Communications, 2011
By near-field optics, we characterized the local optical properties of clusters of gold nanoparti... more By near-field optics, we characterized the local optical properties of clusters of gold nanoparticles randomly distributed under a 50 nm-thick SiO 2 thin film. A local field enhancement is visible above isolated clusters. A few hundred nanometers away from them, we observed a polarization-dependent pattern with elliptical lobes oriented in the incident polarization direction. A simple simulation shows that the observed near-field images can be represented by the sum of the field of an oscillating dipole and the incident field. When the cluster density is larger, the measured near-field images show numerous bright and dark spots. The position of the bright spots does not necessarily coincide with the gold clusters showing the presence of coupling effects between them.
Nature Materials, 2009
In the field of molecular spintronics 1 , the use of magnetic molecules for information technolog... more In the field of molecular spintronics 1 , the use of magnetic molecules for information technology is a main target and the observation of magnetic hysteresis on individual molecules organized on surfaces is a necessary step to develop molecular memory arrays. Although simple paramagnetic molecules can show surface-induced magnetic ordering and hysteresis when deposited on ferromagnetic surfaces 2 , information storage at the molecular level requires molecules exhibiting an intrinsic remnant magnetization, like the so-called singlemolecule magnets 3 (SMMs). These have been intensively investigated for their rich quantum behaviour 4 but no magnetic hysteresis has been so far reported for monolayers of SMMs on various non-magnetic substrates, most probably owing to the chemical instability of clusters on surfaces 5 . Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism synchrotron-based techniques, pushed to the limits in sensitivity and operated at sub-kelvin temperatures, we have now found that robust, tailor-made Fe 4 complexes retain magnetic hysteresis at gold surfaces. Our results demonstrate that isolated SMMs can be used for storing information. The road is now open to address individual molecules wired to a conducting surface 6,7 in their blocked magnetization state, thereby enabling investigation of the elementary interactions between electron transport and magnetism degrees of freedom at the molecular scale 8,9 .
Nature, 2010
A fundamental step towards atomic-or molecular-scale spintronic devices has recently been made by... more A fundamental step towards atomic-or molecular-scale spintronic devices has recently been made by demonstrating that the spin of an individual atom deposited on a surface 1 , or of a small paramagnetic molecule embedded in a nanojunction 2 , can be externally controlled. An appealing next step is the extension of such a capability to the field of information storage, by taking advantage of the magnetic bistability and rich quantum behaviour of single-molecule magnets 3-6 (SMMs). Recently, a proof of concept that the magnetic memory effect is retained when SMMs are chemically anchored to a metallic surface 7 was provided. However, control of the nanoscale organization of these complex systems is required for SMMs to be integrated into molecular spintronic devices 8,9 . Here we show that a preferential orientation of Fe 4 complexes on a gold surface can be achieved by chemical tailoring. As a result, the most striking quantum feature of SMMs-their stepped hysteresis loop, which results from resonant quantum tunnelling of the magnetization 5,6 -can be clearly detected using synchrotron-based spectroscopic techniques. With the aid of multiple theoretical approaches, we relate the angular dependence of the quantum tunnelling resonances to the adsorption geometry, and demonstrate that molecules predominantly lie with their easy axes close to the surface normal. Our findings prove that the quantum spin dynamics can be observed in SMMs chemically grafted to surfaces, and offer a tool to reveal the organization of matter at the nanoscale.
Nanoscale, 2010
We present a novel additive process, which allows the spatially controlled integration of nanopar... more We present a novel additive process, which allows the spatially controlled integration of nanoparticles (NPs) inside silicon surfaces. The NPs are placed between a conductive stamp and a silicon surface; by applying a bias voltage a SiO 2 layer grows underneath the stamp protrusions, thus embedding the particles. We report the successful nanoembedding of CoFe 2 O 4 nanoparticles patterned in lines, grids and logic structures.
Nanoscale, 2013
We describe an environmentally friendly, top-down approach to the synthesis of Au 89 Fe 11 nanopa... more We describe an environmentally friendly, top-down approach to the synthesis of Au 89 Fe 11 nanoparticles (NPs). The plasmonic response of the gold moiety and the magnetism of the iron moiety coexist in the Au 89 Fe 11 nanoalloy with strong modification compared to single element NPs, revealing a non-linear surface plasmon resonance dependence on the iron fraction and a transition from paramagnetic to a spin-glass state at low temperature. These nanoalloys are accessible to conjugation with thiolated molecules and they are promising contrast agents for magnetic resonance imaging. † Electronic supplementary information (ESI) available: TEM images, size histogram, HRTEM images and EFTEM mapping of PEG-AuFeNPs; temperature dependence of c 00 ; calibration curve for analysis of XRD data. See
Nature, 2010
A fundamental step towards atomic-or molecular-scale spintronic devices has recently been made by... more A fundamental step towards atomic-or molecular-scale spintronic devices has recently been made by demonstrating that the spin of an individual atom deposited on a surface 1 , or of a small paramagnetic molecule embedded in a nanojunction 2 , can be externally controlled. An appealing next step is the extension of such a capability to the field of information storage, by taking advantage of the magnetic bistability and rich quantum behaviour of single-molecule magnets 3-6 (SMMs). Recently, a proof of concept that the magnetic memory effect is retained when SMMs are chemically anchored to a metallic surface 7 was provided. However, control of the nanoscale organization of these complex systems is required for SMMs to be integrated into molecular spintronic devices 8,9 . Here we show that a preferential orientation of Fe 4 complexes on a gold surface can be achieved by chemical tailoring. As a result, the most striking quantum feature of SMMs-their stepped hysteresis loop, which results from resonant quantum tunnelling of the magnetization 5,6 -can be clearly detected using synchrotron-based spectroscopic techniques. With the aid of multiple theoretical approaches, we relate the angular dependence of the quantum tunnelling resonances to the adsorption geometry, and demonstrate that molecules predominantly lie with their easy axes close to the surface normal. Our findings prove that the quantum spin dynamics can be observed in SMMs chemically grafted to surfaces, and offer a tool to reveal the organization of matter at the nanoscale.
Magneto-optical (MO) techniques are well-established procedures to characterize the dynamics and ... more Magneto-optical (MO) techniques are well-established procedures to characterize the dynamics and reversal process of nanostructured materials and surfaces. At the same time MO properties include information on the band structure because MO effects are produced by the spin-orbit coupling. This interaction is largely modified in nanomaterials due to quantum confinement effects, changes in the electronic structure and surface contribution. Electronic plasmon excitations, typical of metal nanostructures, can also affect the MO response and the magnetic dynamics. Moreover the interaction between femtosecond light and magnetic materials can produce changes in the dynamic of the reversal process. As a consequence MO studies are emerging as fundamental methods to investigate the correlations between the magnetic, optical and electronic properties of nano-sized materials with an important role for understanding the possibility of manipulation of the magnetic information with light. In our pr...
Page 1. XMCD FOR THE INVESTIGATION OF SINGLE MOLECULE MAGNETS BASED SELF-ASSEMBLED MONOLAYERS Mat... more Page 1. XMCD FOR THE INVESTIGATION OF SINGLE MOLECULE MAGNETS BASED SELF-ASSEMBLED MONOLAYERS Matteo MANNINI,a Philippe SAINCTAVIT,b Chiara DANIELI,c Francesco PINEIDER,a Christophe CARTIER ...
ABSTRACT A detailed study of the composition and structure of Co-doped maghemite nanoparticles wi... more ABSTRACT A detailed study of the composition and structure of Co-doped maghemite nanoparticles with systematically varying composition has been carried out by Transmission Electron Microscopy (TEM) techniques, such as high resolution TEM (HRTEM), scanning TEM (STEM) and Energy Dispersive X-ray Spectrometry (EDS), and by X-ray absorption spectroscopy (XAS) at the Fe and Co K-edges, analyzing both the Extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near edge structure (XANES) regions. The latter techniques in particular, allow us to determine the degree of inversion of divalent and trivalent metal ions among the octahedral and tetrahedral sites in the spinel structure of the nanoparticles and gives detailed information on atomic distances. The samples consist of single-crystal nanoparticles with a composition corresponding to the Fe/Co ratio used in the synthesis. The degree of inversion is quite similar for all samples and close to the value found in a pure cobalt ferrite bulk sample.
We present the magnetic, optical and relaxometric properties of multifunctional Au-Fe 3 O 4 hybri... more We present the magnetic, optical and relaxometric properties of multifunctional Au-Fe 3 O 4 hybrid nanoparticles (HNPs), as possible novel contrast agents (CAs) for magnetic resonance imaging (MRI). The HNPs have been synthesized by wet chemical methods in heterodimer and core-shell geometries and capped with oleylamine. Structural characterization of the samples have been made by X-ray diffraction and transmission electron microscopy, while magnetic properties have been investigated by means of Superconducting Quantum Interference Device-SQUID magnetometry experiments. As required for MRI applications using negative CAs, the samples resulted superparamagnetic at room temperature and well above their blocking temperatures. Optical properties have been investigated by analyzing the optical absorbtion spectra collected in UV-visible region. Relaxometric measurements have been performed on organic suspensions of HNPs and Nuclear Magnetic Resonance (NMR) dispersion curves have been obtained by measuring the longitudinal 1/T 1 and transverse 1/T 2 relaxation rates of solvent protons in the range 10 kHz/300 MHz at room temperature. NMR relaxivities r 1 and r 2 have been compared with ENDOREM s , one of the commercial superparamagnetic iron oxide based MRI contrast agents. MRI contrast enhancement efficiencies have been investigated also by examining T 2 -weighted MR images of suspensions. The experimental results suggest that the nanoparticles' suspensions are good candidates as negative CAs.
The Journal of Physical Chemistry C, 2015
We report a broadband 1 H NMR study of the spin dynamics of coated maghemite and gold−maghemite h... more We report a broadband 1 H NMR study of the spin dynamics of coated maghemite and gold−maghemite hybrid nanostructures with two different geometries, namely dimers and core−shells. All the samples have a superparamagnetic behavior, displaying a blocking temperature (T B ∼ 80 K (maghemite), ∼105 K (dimer), ∼150 K (core−shell)), and the magnetization reversal time follows the Vogel−Fulcher law. We observed three different anomalies in 1 H NMR T 1 −1 versus T that decrease in amplitude when increasing the applied magnetic field. We suggest that the anomalies are related to three distinct system dynamics: molecular rotations of the organic groups (240 < T < 270 K), superparamagnetic spin blockage (100 < T < 150 K), and surface−core spin dynamics (T < 25 K). By fitting the T 1 −1 data with a heuristic model, we achieved a good agreement with magnetic relaxation data and literature values for methyl group rotation frequencies.
Journal of Materials Chemistry C, 2013
ABSTRACT Terbium(III) bis-phthalocyaninato neutral complex, a robust and evaporable Single Molecu... more ABSTRACT Terbium(III) bis-phthalocyaninato neutral complex, a robust and evaporable Single Molecule Magnet (SMM) with a record height of the anisotropy barrier, has recently attracted a great interest as an active unit in single molecule electronics, but at the same time its magnetic hysteresis has been found to be strongly affected when the environment is different from the crystalline phase. Here we present a systematic investigation of the magnetization dynamics in different environments, obtained by magnetic dilution, thermal treatment and sublimation of the molecules, to shed some light on the origin of the evanescence of the hysteretic behavior of this unique SMM.
Springer Proceedings in Physics, 2010
Molecular magnetism is here presented with emphasis concerning the single molecule magnets (SMMs)... more Molecular magnetism is here presented with emphasis concerning the single molecule magnets (SMMs). The architecture of SMMs is reviewed as well as the various ingredients promoting magnetic anisotropy and the relation between magnetic anisotropy and the dynamics of magnetization. Then it is shown how XAS and XMCD can be unique tools to unravel the magnetic properties of SMM submonolayers grafted on clean surfaces. We bring a special attention to the spectral features associated with the magnetic anisotropy and magnetization dynamics.
Chemistry of Materials, 2015
ABSTRACT In iron oxide nanoparticles the transformation of the metastable magnetite phase to magh... more ABSTRACT In iron oxide nanoparticles the transformation of the metastable magnetite phase to maghemite, through the oxidation of iron, often represents a major drawback for correct interpretation of their physical properties and their effective use in several applicative areas. To solve this issue we propose an innovative method for identifying the chemical composition of complex ferrite nanostructures based on magneto-optical (MO) spectroscopy. Spherical iron oxide nanoparticles with increasing size are investigated by magnetic circular dichroism (MCD) in the nUV-vis-nIR range (350-1000 nm). Particular attention is dedicated to the time evolution of the MO response, which is ascribable to the oxidation process of the nanomaterial. The measured MCD spectra show a complex line shape due to the overlap of several MO transitions. Deconvolution analysis of MCD hysteresis loops allows the interpretation of this complex response as the combination of two distinct contributions, originating from magnetite and maghemite domains in the nanoparticles. We consider this method a viable complement to conventional techniques for the discrimination of the two magnetic phases in nanostructured materials.
Nano Letters, 2014
Advanced nanostructured materials, such as gold nanoparticles, magnetic nanoparticles, and multif... more Advanced nanostructured materials, such as gold nanoparticles, magnetic nanoparticles, and multifunctional materials, are nowadays used in many state-of-the-art biomedical application. However, although the engineering in this field is very advanced, there remain some fundamental problems involving the interaction mechanisms between nanostructures and cells or tissues. Here we show the potential of 1 H NMR in the investigation of the uptake of two different kinds of nanostructures, that is, maghemite and gold nanoparticles, and of a chemotherapy drug (Temozolomide) in glioblastoma tumor cells. The proposed experimental protocol provides a new way to investigate the general problem of cellular uptake for a variety of biocompatible nanostructures and drugs.
The Journal of Physical Chemistry C, 2012
ABSTRACT We present a study of the structural, magnetic, and magneto-optical properties of a seri... more ABSTRACT We present a study of the structural, magnetic, and magneto-optical properties of a series of Co-substituted ferrite nanoparticles (NPs) prepared by thermal decomposition of metallo-organic precursors in high boiling solvents. The structural characterization, carried out by using several techniques (transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and magnetic circular dichroism measurements), showed all the samples are high crystalline, 5–6 nm spherical NPs with the cubic spinel structure typical of ferrites. The evolution of lattice parameters with cobalt content suggests that the material is Co-substituted maghemite, also confirmed by XAS and magneto optical (MO) characterizations. The investigation of the magnetic and magneto-optical properties displays peculiar trends with the cobalt content, the main features being the large increase of the saturation magnetization and the anomalous dependence of magnetic anisotropy which reaches its maximum values for intermediate compositions. The large tuneability of this material makes it possible to implement the performances of devices used in biomedical and sensing applications.
Soft Matter, 2011
The paper describes the effect of a low-frequency alternating magnetic field (LF-AMF) on the perm... more The paper describes the effect of a low-frequency alternating magnetic field (LF-AMF) on the permeability and release properties of large (LUVs) and giant (GUVs) unilamellar vesicles loaded with citrate coated cobalt ferrite nanoparticles (NPs). The citrate shell allows a high loading of NPs in lipid vesicles without modifying their magnetic properties. The increase of magnetic LUVs permeability upon exposure to LF-AMF has been evaluated as the fluorescence self-quenching of carboxyfluorescein (CF) entrapped inside the liposome aqueous pool. Liposome leakage has been monitored as a function of field frequency, time exposure and concentration of the citrate coated NPs. Confocal Laser Scanning Microscopy (CLSM) experiments performed on magnetic GUVs labeled with the fluorescent probe DiIC 18 and loaded with Alexa 488-C5-maleimide fluorescent dye provided insights on the release mechanism induced by LF-AMF. The results show that LF-AMF strongly affects vesicles permeability, suggesting the formation of pores in the lipid bilayer due to both hyperthermic effects and nanoparticle oscillations in the vesicles pool at the applied frequency. The behaviour of these magnetic vesicles in the presence of LF-AMF makes this system a good candidate for controlled drug delivery. † Electronic supplementary information (ESI) available: Cryo-TEM images of magnetoliposomes, AC-measurements on powder samples of citrate-coated and uncoated Cobalt ferrite nanoparticles, picture of the magnet used to apply the LF-AMF, measurements of the magnetic field anisotropy of the magnet at different positions. See
Optics Communications, 2011
By near-field optics, we characterized the local optical properties of clusters of gold nanoparti... more By near-field optics, we characterized the local optical properties of clusters of gold nanoparticles randomly distributed under a 50 nm-thick SiO 2 thin film. A local field enhancement is visible above isolated clusters. A few hundred nanometers away from them, we observed a polarization-dependent pattern with elliptical lobes oriented in the incident polarization direction. A simple simulation shows that the observed near-field images can be represented by the sum of the field of an oscillating dipole and the incident field. When the cluster density is larger, the measured near-field images show numerous bright and dark spots. The position of the bright spots does not necessarily coincide with the gold clusters showing the presence of coupling effects between them.
Nature Materials, 2009
In the field of molecular spintronics 1 , the use of magnetic molecules for information technolog... more In the field of molecular spintronics 1 , the use of magnetic molecules for information technology is a main target and the observation of magnetic hysteresis on individual molecules organized on surfaces is a necessary step to develop molecular memory arrays. Although simple paramagnetic molecules can show surface-induced magnetic ordering and hysteresis when deposited on ferromagnetic surfaces 2 , information storage at the molecular level requires molecules exhibiting an intrinsic remnant magnetization, like the so-called singlemolecule magnets 3 (SMMs). These have been intensively investigated for their rich quantum behaviour 4 but no magnetic hysteresis has been so far reported for monolayers of SMMs on various non-magnetic substrates, most probably owing to the chemical instability of clusters on surfaces 5 . Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism synchrotron-based techniques, pushed to the limits in sensitivity and operated at sub-kelvin temperatures, we have now found that robust, tailor-made Fe 4 complexes retain magnetic hysteresis at gold surfaces. Our results demonstrate that isolated SMMs can be used for storing information. The road is now open to address individual molecules wired to a conducting surface 6,7 in their blocked magnetization state, thereby enabling investigation of the elementary interactions between electron transport and magnetism degrees of freedom at the molecular scale 8,9 .
Nature, 2010
A fundamental step towards atomic-or molecular-scale spintronic devices has recently been made by... more A fundamental step towards atomic-or molecular-scale spintronic devices has recently been made by demonstrating that the spin of an individual atom deposited on a surface 1 , or of a small paramagnetic molecule embedded in a nanojunction 2 , can be externally controlled. An appealing next step is the extension of such a capability to the field of information storage, by taking advantage of the magnetic bistability and rich quantum behaviour of single-molecule magnets 3-6 (SMMs). Recently, a proof of concept that the magnetic memory effect is retained when SMMs are chemically anchored to a metallic surface 7 was provided. However, control of the nanoscale organization of these complex systems is required for SMMs to be integrated into molecular spintronic devices 8,9 . Here we show that a preferential orientation of Fe 4 complexes on a gold surface can be achieved by chemical tailoring. As a result, the most striking quantum feature of SMMs-their stepped hysteresis loop, which results from resonant quantum tunnelling of the magnetization 5,6 -can be clearly detected using synchrotron-based spectroscopic techniques. With the aid of multiple theoretical approaches, we relate the angular dependence of the quantum tunnelling resonances to the adsorption geometry, and demonstrate that molecules predominantly lie with their easy axes close to the surface normal. Our findings prove that the quantum spin dynamics can be observed in SMMs chemically grafted to surfaces, and offer a tool to reveal the organization of matter at the nanoscale.
Nanoscale, 2010
We present a novel additive process, which allows the spatially controlled integration of nanopar... more We present a novel additive process, which allows the spatially controlled integration of nanoparticles (NPs) inside silicon surfaces. The NPs are placed between a conductive stamp and a silicon surface; by applying a bias voltage a SiO 2 layer grows underneath the stamp protrusions, thus embedding the particles. We report the successful nanoembedding of CoFe 2 O 4 nanoparticles patterned in lines, grids and logic structures.
Nanoscale, 2013
We describe an environmentally friendly, top-down approach to the synthesis of Au 89 Fe 11 nanopa... more We describe an environmentally friendly, top-down approach to the synthesis of Au 89 Fe 11 nanoparticles (NPs). The plasmonic response of the gold moiety and the magnetism of the iron moiety coexist in the Au 89 Fe 11 nanoalloy with strong modification compared to single element NPs, revealing a non-linear surface plasmon resonance dependence on the iron fraction and a transition from paramagnetic to a spin-glass state at low temperature. These nanoalloys are accessible to conjugation with thiolated molecules and they are promising contrast agents for magnetic resonance imaging. † Electronic supplementary information (ESI) available: TEM images, size histogram, HRTEM images and EFTEM mapping of PEG-AuFeNPs; temperature dependence of c 00 ; calibration curve for analysis of XRD data. See