Rym Boubekri - Academia.edu (original) (raw)

Papers by Rym Boubekri

ACS Nano, 2012

We present a new approach for homogeneous real-time immunodiagnostics (denoted as &am... more We present a new approach for homogeneous real-time immunodiagnostics (denoted as "PlasMag") that can be directly carried out in sample solutions such as serum, thus promising to circumvent the need of sample preparation. It relies on highly sensitive plasmon-optical detection of the relaxation dynamics of magnetic nanoparticles immersed in the sample solution, which changes when target molecules bind to the surfaces of the nanoparticles due to the increase in their hydrodynamic radii. This method requires hybrid nanoparticles that combine both magnetic and optical anisotropic properties. Our model calculations show that core-shell nanorods with a cobalt core diameter of 6 nm, a cobalt core length of 80 nm, and a gold shell thickness of 5 nm are ideally suited as nanoprobes. On the one hand, the spectral position of the longitudinal plasmon resonance of such nanoprobes lies in the near-infrared, where the optical absorption in serum is minimal. On the other hand, the expected change in their relaxation properties on analyte binding is maximal for rotating magnetic fields as excitation in the lower kHz regime. In order to achieve high alignment ratios of the nanoprobes, the strength of the magnetic field should be around 5 mT. While realistic distributions of the nanoprobe properties result in a decrease of their mean optical extinction, the actual relaxation signal change on analyte binding is largely unaffected. These model calculations are supported by measurements on plain cobalt nanorod dispersions, which are the base component of the aspired core-shell nanoprobes currently under development.

Nano Research, 2015

The diameter dependence of the coercivity of cobalt nanowires is quantitatively described by micr... more The diameter dependence of the coercivity of cobalt nanowires is quantitatively described by micromagnetic modelling, which reveals that the magnetization reversal is driven by nucleation at the edges or at stacking faults F. Ott, www-llb.cea.fr G. Viau, www.lpcno.

The Journal of Physical Chemistry C, 2012

ABSTRACT This paper describes specific and nondestructive detection of two isomers of diarylethen... more ABSTRACT This paper describes specific and nondestructive detection of two isomers of diarylethene derivative, namely 1,2-bis (5'-ethoxy-2'-(2 "-pyridyl)thiazolyl)perfluorocyclopentene (DE) by surface-enhanced Raman scattering (SERS). UV and visible light irradiations transform reversibly DE between open-form (OF) and closed-form (CF) isomers, respectively. A mixture of poly(methyl methacrylate) and DE was spin-coated onto gold nanoparticles (GNP) aggregates, which support localized surface plasmon (LSP) in the near-infrared (NIR) region, leading to significant SERS enhancement when 785 nm laser excitation was used. SERS experiments showed that the SEAS spectrum of the CF isomer is clearly distinguished from that of the OF isomer with a strong contrast. A comparison between photoisomerization kinetics obtained from SERS measurements recorded at 633 and 785 nm excitation revealed that excitation in the NIR enables less destructive detection of isomeric states compared to visible excitation. However, weak photoisomerization was detected even with the NIR excitation. We discuss possible mechanisms at the origin of the observed NIR ring-opening process.

Journal of Solid State Chemistry, 2013

We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparti... more We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles ( $ 10) at high temperatures (up to 623 K) using in-situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by m 0 H C ¼ 2(K MC þK shape )/M S with K MC the magnetocrystalline anisotropy constant, K shape the shape anisotropy constant and M S the saturation magnetization. H C decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500 K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300-500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation.

Journal of Raman Spectroscopy, 2013

In this paper, the photochromic reaction of the 1,2-bis(5′-ethoxy-2′-(2″-pyridyl) thiazolyl) comp... more In this paper, the photochromic reaction of the 1,2-bis(5′-ethoxy-2′-(2″-pyridyl) thiazolyl) compound (named DE) was studied by ultraviolet-visible absorption and various Raman spectroscopies associated with density functional theory calculations. To explain the growth of the visible absorption spectrum when the compound is irradiated with ultraviolet light, we suggest the existence of several conformations of the colored form. We also studied the vibrational spectroscopic properties of DE in different conditions such as powder, thin solid film, or in gold nanorods colloidal solutions. This compound is found photochromic in all these conditions. The theoretical Raman spectra of the open and closed forms reproduce fairly well the experimental data and help the complete assignment of the observed bands.

ACS Nano, 2012

We present a new approach for homogeneous real-time immunodiagnostics (denoted as &am... more We present a new approach for homogeneous real-time immunodiagnostics (denoted as "PlasMag") that can be directly carried out in sample solutions such as serum, thus promising to circumvent the need of sample preparation. It relies on highly sensitive plasmon-optical detection of the relaxation dynamics of magnetic nanoparticles immersed in the sample solution, which changes when target molecules bind to the surfaces of the nanoparticles due to the increase in their hydrodynamic radii. This method requires hybrid nanoparticles that combine both magnetic and optical anisotropic properties. Our model calculations show that core-shell nanorods with a cobalt core diameter of 6 nm, a cobalt core length of 80 nm, and a gold shell thickness of 5 nm are ideally suited as nanoprobes. On the one hand, the spectral position of the longitudinal plasmon resonance of such nanoprobes lies in the near-infrared, where the optical absorption in serum is minimal. On the other hand, the expected change in their relaxation properties on analyte binding is maximal for rotating magnetic fields as excitation in the lower kHz regime. In order to achieve high alignment ratios of the nanoprobes, the strength of the magnetic field should be around 5 mT. While realistic distributions of the nanoprobe properties result in a decrease of their mean optical extinction, the actual relaxation signal change on analyte binding is largely unaffected. These model calculations are supported by measurements on plain cobalt nanorod dispersions, which are the base component of the aspired core-shell nanoprobes currently under development.

Chemistry of Materials, 2009

ABSTRACT Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-pr... more ABSTRACT Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-produced crystals are paramagnetic. However, heating at 400 °C under a nitrogen atmosphere for 1 h induces ferromagnetism at room temperature, characterized by coercive field (0.38 kOe) and magnetization at 10 kOe (0.10 μB/Co) similar to the values reported recently for nanocrystalline Co:ZnO aggregates. To understand this evolution, we have characterized the samples by chemical and physical analyses including X-ray diffraction (XRD), transmission electron microscopy (TEM), UV−visible−IR absorption spectroscopy, magnetic measurements, and EPR experiments. These analyses show that the Co ions are incorporated into the wurtzite structure, forming a Zn1−xCoxO solid solution. X-ray diffraction and electron microscopy failed to detect secondary phases, neither before nor after the thermal treatment. However, the shape of the nanoparticles is modified and becomes more spherical upon annealing, which gives evidence of an important diffusion of atomic species. X-band electron paramagnetic resonance (EPR) reveals the presence of magnetic clusters in the annealed samples. Both the magnetic and optical properties show that these are Co clusters that have grown at the expense of the cobalt diluted in the host matrix. The thermal treatment survey performed by thermogravimetric analysis coupled with mass spectrometry and IR spectroscopy gives evidence of desorption of organic species and liberation of oxygen from the surface of the particles. This study then suggests that the origin of the magnetism believed to be intrinsic to the material in many prior works is extrinsic in nature and is due to the diffusion of cobalt and oxygen species at the surface of the particles, where Co forms nanoclusters while most of the oxygen is liberated in the annealing process.

ACS Nano, 2012

We present a new approach for homogeneous real-time immunodiagnostics (denoted as &am... more We present a new approach for homogeneous real-time immunodiagnostics (denoted as "PlasMag") that can be directly carried out in sample solutions such as serum, thus promising to circumvent the need of sample preparation. It relies on highly sensitive plasmon-optical detection of the relaxation dynamics of magnetic nanoparticles immersed in the sample solution, which changes when target molecules bind to the surfaces of the nanoparticles due to the increase in their hydrodynamic radii. This method requires hybrid nanoparticles that combine both magnetic and optical anisotropic properties. Our model calculations show that core-shell nanorods with a cobalt core diameter of 6 nm, a cobalt core length of 80 nm, and a gold shell thickness of 5 nm are ideally suited as nanoprobes. On the one hand, the spectral position of the longitudinal plasmon resonance of such nanoprobes lies in the near-infrared, where the optical absorption in serum is minimal. On the other hand, the expected change in their relaxation properties on analyte binding is maximal for rotating magnetic fields as excitation in the lower kHz regime. In order to achieve high alignment ratios of the nanoprobes, the strength of the magnetic field should be around 5 mT. While realistic distributions of the nanoprobe properties result in a decrease of their mean optical extinction, the actual relaxation signal change on analyte binding is largely unaffected. These model calculations are supported by measurements on plain cobalt nanorod dispersions, which are the base component of the aspired core-shell nanoprobes currently under development.

Nano Research, 2015

The diameter dependence of the coercivity of cobalt nanowires is quantitatively described by micr... more The diameter dependence of the coercivity of cobalt nanowires is quantitatively described by micromagnetic modelling, which reveals that the magnetization reversal is driven by nucleation at the edges or at stacking faults F. Ott, www-llb.cea.fr G. Viau, www.lpcno.

The Journal of Physical Chemistry C, 2012

ABSTRACT This paper describes specific and nondestructive detection of two isomers of diarylethen... more ABSTRACT This paper describes specific and nondestructive detection of two isomers of diarylethene derivative, namely 1,2-bis (5'-ethoxy-2'-(2 "-pyridyl)thiazolyl)perfluorocyclopentene (DE) by surface-enhanced Raman scattering (SERS). UV and visible light irradiations transform reversibly DE between open-form (OF) and closed-form (CF) isomers, respectively. A mixture of poly(methyl methacrylate) and DE was spin-coated onto gold nanoparticles (GNP) aggregates, which support localized surface plasmon (LSP) in the near-infrared (NIR) region, leading to significant SERS enhancement when 785 nm laser excitation was used. SERS experiments showed that the SEAS spectrum of the CF isomer is clearly distinguished from that of the OF isomer with a strong contrast. A comparison between photoisomerization kinetics obtained from SERS measurements recorded at 633 and 785 nm excitation revealed that excitation in the NIR enables less destructive detection of isomeric states compared to visible excitation. However, weak photoisomerization was detected even with the NIR excitation. We discuss possible mechanisms at the origin of the observed NIR ring-opening process.

Journal of Solid State Chemistry, 2013

We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparti... more We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles ( $ 10) at high temperatures (up to 623 K) using in-situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by m 0 H C ¼ 2(K MC þK shape )/M S with K MC the magnetocrystalline anisotropy constant, K shape the shape anisotropy constant and M S the saturation magnetization. H C decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500 K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300-500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation.

Journal of Raman Spectroscopy, 2013

In this paper, the photochromic reaction of the 1,2-bis(5′-ethoxy-2′-(2″-pyridyl) thiazolyl) comp... more In this paper, the photochromic reaction of the 1,2-bis(5′-ethoxy-2′-(2″-pyridyl) thiazolyl) compound (named DE) was studied by ultraviolet-visible absorption and various Raman spectroscopies associated with density functional theory calculations. To explain the growth of the visible absorption spectrum when the compound is irradiated with ultraviolet light, we suggest the existence of several conformations of the colored form. We also studied the vibrational spectroscopic properties of DE in different conditions such as powder, thin solid film, or in gold nanorods colloidal solutions. This compound is found photochromic in all these conditions. The theoretical Raman spectra of the open and closed forms reproduce fairly well the experimental data and help the complete assignment of the observed bands.

ACS Nano, 2012

We present a new approach for homogeneous real-time immunodiagnostics (denoted as &am... more We present a new approach for homogeneous real-time immunodiagnostics (denoted as "PlasMag") that can be directly carried out in sample solutions such as serum, thus promising to circumvent the need of sample preparation. It relies on highly sensitive plasmon-optical detection of the relaxation dynamics of magnetic nanoparticles immersed in the sample solution, which changes when target molecules bind to the surfaces of the nanoparticles due to the increase in their hydrodynamic radii. This method requires hybrid nanoparticles that combine both magnetic and optical anisotropic properties. Our model calculations show that core-shell nanorods with a cobalt core diameter of 6 nm, a cobalt core length of 80 nm, and a gold shell thickness of 5 nm are ideally suited as nanoprobes. On the one hand, the spectral position of the longitudinal plasmon resonance of such nanoprobes lies in the near-infrared, where the optical absorption in serum is minimal. On the other hand, the expected change in their relaxation properties on analyte binding is maximal for rotating magnetic fields as excitation in the lower kHz regime. In order to achieve high alignment ratios of the nanoprobes, the strength of the magnetic field should be around 5 mT. While realistic distributions of the nanoprobe properties result in a decrease of their mean optical extinction, the actual relaxation signal change on analyte binding is largely unaffected. These model calculations are supported by measurements on plain cobalt nanorod dispersions, which are the base component of the aspired core-shell nanoprobes currently under development.

Chemistry of Materials, 2009

ABSTRACT Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-pr... more ABSTRACT Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-produced crystals are paramagnetic. However, heating at 400 °C under a nitrogen atmosphere for 1 h induces ferromagnetism at room temperature, characterized by coercive field (0.38 kOe) and magnetization at 10 kOe (0.10 μB/Co) similar to the values reported recently for nanocrystalline Co:ZnO aggregates. To understand this evolution, we have characterized the samples by chemical and physical analyses including X-ray diffraction (XRD), transmission electron microscopy (TEM), UV−visible−IR absorption spectroscopy, magnetic measurements, and EPR experiments. These analyses show that the Co ions are incorporated into the wurtzite structure, forming a Zn1−xCoxO solid solution. X-ray diffraction and electron microscopy failed to detect secondary phases, neither before nor after the thermal treatment. However, the shape of the nanoparticles is modified and becomes more spherical upon annealing, which gives evidence of an important diffusion of atomic species. X-band electron paramagnetic resonance (EPR) reveals the presence of magnetic clusters in the annealed samples. Both the magnetic and optical properties show that these are Co clusters that have grown at the expense of the cobalt diluted in the host matrix. The thermal treatment survey performed by thermogravimetric analysis coupled with mass spectrometry and IR spectroscopy gives evidence of desorption of organic species and liberation of oxygen from the surface of the particles. This study then suggests that the origin of the magnetism believed to be intrinsic to the material in many prior works is extrinsic in nature and is due to the diffusion of cobalt and oxygen species at the surface of the particles, where Co forms nanoclusters while most of the oxygen is liberated in the annealing process.