Publications by authors named "Thierry Gacoin"

66 Publications

Measuring 3D orientation of nanocrystals via polarized luminescence of rare-earth dopants.

Nat Commun 2021 03 29;12(1):1943. Epub 2021 Mar 29.

Laboratoire de Physique de la Matière Condensée, CNRS, École Polytechnique, Institut Polytechnique de Paris, Palaiseau, France.

Orientation of nanoscale objects can be measured by examining the polarized emission of optical probes. To retrieve a three-dimensional (3D) orientation, it has been essential to observe the probe (a dipole) along multiple viewing angles and scan with a rotating analyzer. However, this method requires a sophisticated optical setup and is subject to various external sources of error. Here, we present a fundamentally different approach employing coupled multiple emission dipoles that are inherent in lanthanide-doped phosphors. Simultaneous observation of different dipoles and comparison of their relative intensities allow to determine the 3D orientation from a single viewing angle. Moreover, the distinct natures of electric and magnetic dipoles originating in lanthanide luminescence enable an instant orientation analysis with a single-shot emission spectrum. We demonstrate a straightforward orientation analysis of Eu-doped NaYF nanocrystals using a conventional fluorescence microscope. Direct imaging of the rod-shaped nanocrystals proved the high accuracy of the measurement. This methodology would provide insights into the mechanical behaviors of various nano- and biomolecular systems.
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http://dx.doi.org/10.1038/s41467-021-22158-4DOI Listing
March 2021

Fast Imaging of SHG Nanoprobes with Multiphoton Light-Sheet Microscopy.

ACS Photonics 2020 Apr 28;7(4):1036-1049. Epub 2020 Feb 28.

Laboratory for Optics and Biosciences, Ecole Polytechnique, CNRS, INSERM, Université Paris-Saclay, 91128 Palaiseau Cedex, France.

Two-photon light-sheet microscopy (2P-SPIM) provides a unique combination of advantages for fast and deep fluorescence imaging in live tissues. Detecting coherent signals such as second-harmonic generation (SHG) in 2P-SPIM in addition to fluorescence would open further imaging opportunities. However, light-sheet microscopy involves an orthogonal configuration of illumination and detection that questions the ability to detect coherent signals. Indeed, coherent scattering from micron-sized structures occurs predominantly along the illumination beam. By contrast, point-like sources such as SHG nanocrystals can efficiently scatter light in multiple directions and be detected using the orthogonal geometry of a light-sheet microscope. This study investigates the suitability of SHG light-sheet microscopy (SHG-SPIM) for fast imaging of SHG nanoprobes. Parameters that govern the detection efficiency of KTiOPO and BaTiO nanocrystals using SHG-SPIM are investigated theoretically and experimentally. The effects of incident polarization, detection numerical aperture, nanocrystal rotational motion, and second-order susceptibility tensor symmetries on the detectability of SHG nanoprobes in this specific geometry are clarified. Guidelines for optimizing SHG-SPIM imaging are established, enabling fast light-sheet imaging combining SHG and two-photon excited fluorescence. Finally, microangiography was achieved in live zebrafish embryos by SHG imaging at up to 180 frames per second and single-particle tracking of SHG nanoprobes in the blood flow.
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http://dx.doi.org/10.1021/acsphotonics.9b01749DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7735018PMC
April 2020

Elaboration of Superparamagnetic and Bioactive Multicore-Shell Nanoparticles (γ-FeO@SiO-CaO): A Promising Material for Bone Cancer Treatment.

ACS Appl Mater Interfaces 2020 Oct 8;12(42):47820-47830. Epub 2020 Oct 8.

CNRS, SIGMA Clermont, ICCF, Université Clermont Auvergne, Clermont-Ferrand F-63000, France.

The past few decades have seen the development of new bone cancer therapies, triggered by the discovery of new biomaterials. When the tumoral area is small and accessible, the common clinical treatment implies the tumor mass removal followed by bone reconstruction or consolidation with a bioceramic or a metallic scaffold. Even though the treatment also involves chemotherapy or radiotherapy, resurgence of cancer cells remains possible. We have thus designed a new kind of heterostructured nanobiomaterial, composed of SiO-CaO bioactive glass as the shell and superparamagnetic γ-FeO iron oxide as the core in order to combine the benefits of bone repair thanks to the glass bioactivity and cancer cell destruction through magnetic hyperthermia. These multifunctional core-shell nanoparticles (NPs) have been obtained using a two-stage procedure, involving the coprecipitation of 11 nm sized iron oxide NPs followed by their encapsulation inside a bioactive glass shell by sol-gel chemistry. The as-produced spherical multicore-shell NPs show a narrow size distribution of 73 ± 7 nm. Magnetothermal loss measurements by calorimetry under an alternating magnetic field and in vitro bioactivity assessment performed in simulated body fluid showed that these heterostructures exhibit a good heating capacity and a fast mineralization process (hydroxyapatite forming ability). In addition, their in vitro cytocompatibility, evaluated in the presence of human mesenchymal stem cells during 3 and 7 days, has been demonstrated. These first findings suggest that γ-FeO@SiO-CaO heterostructures are a promising biomaterial to fill bone defects resulting from bone tumor resection, as they have the ability to both repair bone tissue and act as thermoseeds for cancer therapy.
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http://dx.doi.org/10.1021/acsami.0c12769DOI Listing
October 2020

Toward a Chemical Control of Colloidal YVO Nanoparticles Microstructure.

Langmuir 2020 Aug 30;36(31):9124-9131. Epub 2020 Jul 30.

Laboratoire de Physique de la Matière Condensée, Ecole Polytechnique, CNRS, Université Paris-Saclay, Route de Saclay, 91128 Palaiseau Cedex, France.

Rare-earth-doped oxides are a class of compounds that have been largely studied in the context of the development of luminescent nanocrystals for various applications including fluorescent labels for bioimaging, MRI contrast agents, luminescent nanocomposite coatings, etc. Elaboration of colloidal suspensions is usually achieved through coprecipitation. Particles exhibit emission properties that are similar to the bulk counterparts, although altered by crystalline defects or surface quenching species. Focusing on YVO:Eu, one of the first reported systems, the aim of this work is to revisit the elaboration of nanoparticles obtained through a simple aqueous coprecipitation route. The objective is more precisely to get a better understanding of the parameters affecting the particles' internal microstructure, a feature that is poorly controlled and characterized. We show that the hydroxyl concentration in the precursor solution has a drastic effect on the particles' microstructure. Moreover, discrepancies in the reported particle structure are shown to possibly arise from the carbonation of the strongly basic orthovanadate precursor. For this study, SAXS/WAXS is shown to be a powerful tool to characterize the multiscale structure of the particles. It could be shown that playing on the precursor composition, it may be varied between almost monocrystalline nanocrystals to particles exhibiting a hierarchical microstructure well described by a surface fractal model. This work provides a new methodology for the characterization of nanoparticles microstructure and opens new directions for its optimization in view of applications.
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http://dx.doi.org/10.1021/acs.langmuir.0c01266DOI Listing
August 2020

NaYF Microstructure, beyond Their Well-Shaped Morphology.

Nanomaterials (Basel) 2019 Nov 4;9(11). Epub 2019 Nov 4.

Laboratoire de Physique de la Matière Condensée, École Polytechnique, CNRS, Université Paris Saclay, 91128 Palaiseau, France.

Lanthanide-doped nanoparticles are widely investigated for their optical properties. However, the sensitivity of the lanthanide ions' luminescence to the local symmetry, useful when investigating structural environments, becomes a drawback for optimized properties in the case of poorly controlled crystallinity. In this paper, we focus on β -NaYF nanorods in order to provide a detailed description of their chemical composition and microstructure. The combination of detailed XRD analysis and TEM observations show that strong variation may be observed from particles from a same batch of synthesis, but also when considering small variations of synthesis conditions. Moreover, also the nanorods observed by SEM exhibit a very nice faceted shape, they are far from being monocrystalline and present significant local deviation of crystalline symmetry and orientation. All these structural considerations, sensitively probed by polarized emission analysis, are crucial to analyze for the development of optimal systems toward the targeted applications.
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http://dx.doi.org/10.3390/nano9111560DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6915562PMC
November 2019

Luminescence mechanochromism of copper iodide clusters: a rational investigation.

Dalton Trans 2019 Jun 14;48(22):7899-7909. Epub 2019 May 14.

Laboratoire de Physique de la Matière Condensée (PMC), CNRS - Ecole Polytechnique, 91128 Palaiseau Cedex, France.

The development of luminescent mechanochromic materials depends mainly on the possibility to rationally design them with the desired properties. Molecular copper iodide clusters constitute an unprecedented family of compounds exhibiting great changes of their luminescence properties upon mechanical stress. From previous studies, the mechanochromic properties of cubane [CuIL] (L = organic ligand) clusters have been attributed to modifications of cuprophilic interactions induced by mechanical solicitation. In this study, we ascertain our hypothesis by choosing to study the luminescence mechanochromism of a [CuI(PPh)] cluster which presents two crystalline polymorphs exhibiting strikingly different Cu-Cu bond lengths. As forecasted, only one of these two polymorphs exhibits mechanochromic properties. Structural and optical characterization methods are reported along with structural characterization under controlled pressure allowing a precise analysis of the structural changes occurring under mechanical stress. In addition to confirming our mechanism based on enhancement of cuprophilic interactions under pressure, this study demonstrates the possibility of prediction of mechanochromic properties in the family of copper iodide compounds that constitutes a step further toward the rational design of stimuli-responsive materials.
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http://dx.doi.org/10.1039/c9dt01161gDOI Listing
June 2019

Luminescence Vapochromism of a Dynamic Copper Iodide Mesocate.

Chemistry 2018 Dec 16;24(71):18868-18872. Epub 2018 Nov 16.

Laboratoire de Physique de la Matière Condensée (PMC), Ecole Polytechnique-CNRS, 91128, Palaiseau Cedex, France.

A copper iodide complex coordinated by three phosphine ligands with the formula [Cu I (Ph PC (C H )C PPh ) ] exhibits solvatochromic and vapochromic luminescence properties. A mechanism based on solvent-dependent molecular motion appears to occur. The highly contrasted response observed upon THF solvent exposure makes this complex an appealing candidate for chemical sensor applications.
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http://dx.doi.org/10.1002/chem.201804377DOI Listing
December 2018

Strain engineering of photo-induced phase transformations in Prussian blue analogue heterostructures.

Nanoscale 2018 Aug;10(34):16030-16039

Physique de la Matière Condensée, Ecole Polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France.

Heterostructures based on Prussian blue analogues (PBA) combining photo- and magneto-striction have shown a large potential for the development of light-induced magnetization switching. However, studies of the microscopic parameters that control the transfer of the mechanical stresses across the interface and their propagation in the magnetic material are still too scarce to efficiently improve the elastic coupling. Here, this coupling strength is tentatively controlled by strain engineering in heteroepitaxial PBA core-shell heterostructures involving the same Rb0.5Co[Fe(CN)6]0.8·zH2O photostrictive core and isostructural shells of similar thickness and variable mismatch with the core lattice. The shell deformation and the optical electron transfer at the origin of photostriction are monitored by combined in situ and real time synchrotron X-ray powder diffraction and X-ray absorption spectroscopy under visible light irradiation. These experiments show that rather large strains, up to +0.9%, are developed within the shell in response to the tensile stresses associated with the expansion of the core lattice upon illumination. The shell behavior is, however, complex, with contributions in dilatation, in compression or unchanged. We show that a tailored photo-response in terms of strain amplitude and kinetics with potential applications for a magnetic manipulation using light requires a trade-off between the quality of the interface (which needs a small lattice mismatch i.e. a small a-cubic parameter for the shell) and the shell rigidity (decreased for a large a-parameter). A shell with a high compressibility that is further increased by the presence of misfit dislocations will show a decrease in its mechanical retroaction on the photo-switching properties of the core particles.
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http://dx.doi.org/10.1039/c8nr03597kDOI Listing
August 2018

Tin dioxide nanoparticles as catalyst precursors for plasma-assisted vapor-liquid-solid growth of silicon nanowires with well-controlled density.

Nanotechnology 2018 Oct 3;29(43):435301. Epub 2018 Aug 3.

GeePs, CNRS, CentraleSupelec, Université Paris-Sud, Université Paris-Saclay, Sorbonne Université-UPMC Université Paris 06, 91192 Gif-sur-Yvette Cedex, France. LPICM, CNRS, Ecole Polytechnique, Université Paris-Saclay, F-91128 Palaiseau, France. Physique de la Matière Condensée, CNRS, Ecole Polytechnique, Université Paris-Saclay, F-91128 Palaiseau, France.

The fabrication of arrays of silicon nanowires (Si NWs) with well-defined surface coverage using the vapor-liquid-solid process requires a good control of the density and size distribution for the metal catalyst. We report on a cost-effective bottom-up approach to produce Si NWs by a low-temperature deposition technology using plasma-enhanced chemical vapor deposition and tin dioxide (SnO) nanoparticles as the source of tin catalyst. This strategy offers a straightforward method to select specific particle sizes by conventional colloidal techniques, and to tune the surface coverage using a polyelectrolyte layer to efficiently immobilize the particles on the substrate by electrostatic grafting. After a further step of reduction into tin metal droplets using hydrogen plasma treatment, the catalyst particles are used for the growth of Si NWs. This approach allows the prodcution of controlled Si NWs arrays which can be used as a template for radial junction thin film solar cells.
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http://dx.doi.org/10.1088/1361-6528/aad7dbDOI Listing
October 2018

Polarized Luminescence of Anisotropic LaPO:Eu Nanocrystal Polymorphs.

J Am Chem Soc 2018 08 17;140(30):9512-9517. Epub 2018 Jul 17.

Laboratoire de Physique de la Matière Condensée , Ecole Polytechnique, CNRS, Université Paris-Saclay , 91128 Palaiseau , France.

Lanthanide elements exhibit highly appealing spectroscopic properties that are extensively used for phosphor applications. Their luminescence contains precise information on the internal structure of the host materials. Especially, the polarization behavior of the transition sublevel peaks is a fingerprint of the crystal phase, symmetry, and defects. However, this unique feature is poorly explored in current research on lanthanide nanophosphors. We here report on a detailed investigation of the evolution of Eu luminescence during the thermally induced phase transition of LaPO nanocrystal hosts. By means of c-axis-aligned nanocrystal assemblies, we demonstrate a dramatic change of the emission polarization feature corresponding to the distinct Eu site symmetries in different LaPO polymorphs. We also show that changes of the nanocrystal structure can be identified by this spectroscopic method, with a much higher sensitivity than the X-ray diffraction analysis. This new insight into the nanostructure-luminescence relationship, associated with the unprecedented polarization characterizations, provides a new methodology to investigate phase transitions in nanomaterials. It also suggests a novel function of lanthanide emitters as orientation-sensing nanoprobes for innovative applications such as in bioimaging or microfluidics.
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http://dx.doi.org/10.1021/jacs.8b03983DOI Listing
August 2018

Enhancing Magnetic Light Emission with All-Dielectric Optical Nanoantennas.

Nano Lett 2018 06 2;18(6):3481-3487. Epub 2018 May 2.

ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology , Castelldefels , 08860 Barcelona , Spain.

Electric and magnetic optical fields carry the same amount of energy. Nevertheless, the efficiency with which matter interacts with electric optical fields is commonly accepted to be at least 4 orders of magnitude higher than with magnetic optical fields. Here, we experimentally demonstrate that properly designed photonic nanoantennas can selectively manipulate the magnetic versus electric emission of luminescent nanocrystals. In particular, we show selective enhancement of magnetic emission from trivalent europium-doped nanoparticles in the vicinity of a nanoantenna tailored to exhibit a magnetic resonance. Specifically, by controlling the spatial coupling between emitters and an individual nanoresonator located at the edge of a near-field optical scanning tip, we record with nanoscale precision local distributions of both magnetic and electric radiative local densities of states (LDOS). The map of the radiative LDOS reveals the modification of both the magnetic and electric quantum environments induced by the presence of the nanoantenna. This manipulation and enhancement of magnetic light-matter interaction by means of nanoantennas opens up new possibilities for the research fields of optoelectronics, chiral optics, nonlinear and nano-optics, spintronics, and metamaterials, among others.
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http://dx.doi.org/10.1021/acs.nanolett.8b00548DOI Listing
June 2018

Evaluation of Ligands Effect on the Photophysical Properties of Copper Iodide Clusters.

Inorg Chem 2018 Apr 5;57(8):4328-4339. Epub 2018 Apr 5.

Laboratoire de Physique de la Matière Condensée (PMC) , CNRS-Ecole Polytechnique , 91128 Palaiseau Cedex, France.

Luminescent materials based on copper complexes are currently receiving increasing attention because of their rich photophysical properties, opening a wide field of applications. The copper iodide clusters formulated [CuIL] (L = ligand), are particularly relevant for the development of multifunctional materials based on their luminescence stimuli-responsive properties. In this context, controlling and modulating their photophysical properties is crucial and this can only be achieved by thorough understanding of the origin of the optical properties. We thus report here, the comparative study of a series of cubane copper iodide clusters coordinated by different phosphine ligands, with the goal of analyzing the effect of the ligands nature on the photoluminescence properties. The synthesis, structural, and photophysical characterizations along with theoretical investigations of copper iodide clusters with ligands presenting different electronic properties, are described. A method to simplify the analysis of the P solid-state NMR spectra is also reported. While clusters with electron-donating groups present classical luminescence properties, the cluster bearing strong electron-withdrawing substituents exhibits original behavior demonstrating a clear influence of the ligands properties. In particular, the electron-withdrawing character induces a decrease in energy of the unoccupied molecular orbitals, that consequently impacts the emission properties. The modification of the luminescence thermochromic properties of the clusters are supported by density functional theory (DFT) calculations. This study demonstrates that the control of the luminescence properties of these compounds can be achieved through modification of the coordinated ligands, nevertheless the role of the crystal packing should not be underestimated.
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http://dx.doi.org/10.1021/acs.inorgchem.7b03160DOI Listing
April 2018

Luminescence Mechanochromism Induced by Cluster Isomerization.

Inorg Chem 2017 Oct 26;56(20):12379-12388. Epub 2017 Sep 26.

Institut des Matériaux Jean Rouxel, Université de Nantes, CNRS , 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3, France.

Luminescent mechanochromic materials exhibiting reversible changes of their emissive properties in response to external mechanical forces are currently emerging as an important class of stimuli-responsive materials because of promising technological applications. Here, we report on the luminescence mechanochromic properties of a [CuI(PPh)] copper iodide cluster presenting a chair geometry, being an isomer of the most common cubane form. This molecular cluster formulated [CuI(PPh)]·2CHCl (1) exhibits a highly contrasted emission response to manual grinding, and, interestingly, the optical properties of the ground phase present striking similarities with those of the cubane isomer. In order to understand the underlying mechanism, a comparison with two related compounds has been conducted. The first one is a pseudopolymorph of 1 formulated as [CuI(PPh)]·CHCl (2), which exhibits luminescent mechanochromic properties as well. The other one is also a chair compound but with a slightly different phosphine ligand, namely, [CuI(PPhCHCOH)] (3), lacking mechanochromic properties. Structural and optical characterizations of the clusters have been analyzed in light of previous electronic structure calculations. The results suggest an unpreceded mechanochromism phenomenon based on a solid-state chair → cubane isomer conversion. This study shows that polynuclear copper iodide compounds are particularly relevant for the development of luminescent mechanochromic materials.
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http://dx.doi.org/10.1021/acs.inorgchem.7b01870DOI Listing
October 2017

Metrology of Multiphoton Microscopes Using Second Harmonic Generation Nanoprobes.

Small 2017 11 19;13(42). Epub 2017 Sep 19.

Laboratory for Optics and Biosciences, Ecole Polytechnique, CNRS, INSERM, Université Paris-Saclay, 91128, Palaiseau cedex, France.

In multiphoton microscopy, the ongoing trend toward the use of excitation wavelengths spanning the entire near-infrared range calls for new standards in order to quantify and compare the performances of microscopes. This article describes a new method for characterizing the imaging properties of multiphoton microscopes over a broad range of excitation wavelengths in a straightforward and efficient manner. It demonstrates how second harmonic generation (SHG) nanoprobes can be used to map the spatial resolution, field curvature, and chromatic aberrations across the microscope field of view with a precision below the diffraction limit and with unique advantages over methods based on fluorescence. KTiOPO4 nanocrystals are used as SHG nanoprobes to measure and compare the performances over the 850-1100 nm wavelength range of several microscope objectives designed for multiphoton microscopy. Finally, this approach is extended to the post-acquisition correction of chromatic aberrations in multicolor multiphoton imaging. Overall, the use of SHG nanoprobes appears as a uniquely suited method to standardize the metrology of multiphoton microscopes.
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http://dx.doi.org/10.1002/smll.201701442DOI Listing
November 2017

Monitoring the orientation of rare-earth-doped nanorods for flow shear tomography.

Nat Nanotechnol 2017 09 19;12(9):914-919. Epub 2017 Jun 19.

Laboratoire de Physique de la Matière Condensée, Ecole Polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France.

Rare-earth phosphors exhibit unique luminescence polarization features originating from the anisotropic symmetry of the emitter ion's chemical environment. However, to take advantage of this peculiar property, it is necessary to control and measure the ensemble orientation of the host particles with a high degree of precision. Here, we show a methodology to obtain the photoluminescence polarization of Eu-doped LaPO nanorods assembled in an electrically modulated liquid-crystalline phase. We measure Eu emission spectra for the three main optical configurations (σ, π and α, depending on the direction of observation and the polarization axes) and use them as a reference for the nanorod orientation analysis. Based on the fact that flowing nanorods tend to orient along the shear strain profile, we use this orientation analysis to measure the local shear rate in a flowing liquid. The potential of this approach is then demonstrated through tomographic imaging of the shear rate distribution in a microfluidic system.
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http://dx.doi.org/10.1038/nnano.2017.111DOI Listing
September 2017

Determination of paramagnetic concentrations inside a diamagnetic matrix using solid-state NMR.

Phys Chem Chem Phys 2017 May;19(19):12175-12184

Laboratoire de Physique de la Matière Condensée, École polytechnique, CNRS, Université Paris Saclay, 91128 Palaiseau Cedex, France.

The determination of very low doping levels in solid materials is an important issue for many applications. When considering paramagnetic dopants, the NMR relaxation technique appears to be much more accurate than classical techniques such as Vegard's law resulting from X-ray diffraction (XRD) measurements or chemical analysis that cannot provide information on appropriate dopant spatial distributions. In a recent report, the linear variation of 1/T, i.e. the nuclear relaxation rate, as a function of Nd content has been used to determine doping levels with a good dispersion homogeneity in the monazite LaPO matrix down to 0.1 mol%. We here extend this study to more complex compounds doped with Nd, such as YPO, the solid solution YScPO, Ba(PO)Cl and a phosphate glass. For all considered compounds except Ba(PO)Cl:Nd, 1/T is found to be linearly proportional to the nominal Nd concentration, confirming the ability of the method to investigate the dopant concentration and spatial homogeneity. The results obtained for different compounds open up the discussion on the parameters, such as the orbital overlap and the average P-P distances, influencing the nuclear relaxation rate.
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http://dx.doi.org/10.1039/c7cp00451fDOI Listing
May 2017

Ultra-wide range field-dependent measurements of the relaxivity of GdEuVO nanoparticle contrast agents using a mechanical sample-shuttling relaxometer.

Sci Rep 2017 03 20;7:44770. Epub 2017 Mar 20.

NIMBE, CEA-CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France.

The current trend for Magnetic Resonance Imaging points towards higher magnetic fields. Even though sensitivity and resolution are increased in stronger fields, T1 contrast is often reduced, and this represents a challenge for contrast agent design. Field-dependent measurements of relaxivity are thus important to characterize contrast agents. At present, the field-dependent curves of relaxivity are usually carried out in the field range of 0 T to 2 T, using fast field cycling relaxometers. Here, we employ a high-speed sample shuttling device to switch the magnetic fields experienced by the nuclei between virtually zero field, and the center of any commercial spectrometer. We apply this approach on rare-earth (mixed Gadolinium-Europium) vanadate nanoparticles, and obtain the dispersion curves from very low magnetic field up to 11.7 T. In contrast to the relaxivity profiles of Gd chelates, commonly used for clinical applications, which display a plateau and then a decrease for increasing magnetic fields, these nanoparticles provide maximum contrast enhancement for magnetic fields around 1-1.5 T. These field-dependent curves are fitted using the so-called Magnetic Particle (MP) model and the extracted parameters discussed as a function of particle size and composition. We finally comment on the new possibilities offered by this approach.
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http://dx.doi.org/10.1038/srep44770DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5357940PMC
March 2017

Lanthanoid-Doped Phosphate/Vanadate Mixed Hollow Particles as Ratiometric Luminescent Sensors.

ACS Appl Mater Interfaces 2017 Jan 6;9(2):1635-1644. Epub 2017 Jan 6.

Solid State Chemistry Group/Laboratoire de Physique de la Matière Condensée, Ecole Polytechnique , Route de Saclay, 91128 Palaiseau Cedex, France.

Rare earth (RE) phosphates and vanadates are structurally similar compositions that display distinct but complementary luminescent properties. The properties of these phosphors can be combined in REPO-REVO heterostructures during the development of new sensing technologies for biological applications. This work presents the synthesis of hollow RE phosphate/vanadate colloidal particles and evaluates their applicability as luminescent markers. Hydrothermal treatments of RE hydroxycarbonate particles in the presence of the PO and VO precursors afforded the final REPO-REVO solids in a two-step template synthesis. We converted precursor hydroxycarbonate particles into the final heterostructures and characterized their structure and morphology. According to our detailed study into the spectroscopic properties of Eu-doped particles and their luminescence response to several species, the presence of the phosphate and vanadate phases in a single particle provided different chemical environments and enabled the design of a ratiometric approach to detect HO. These results open new perspectives for the development of new intracellular luminescent markers.
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http://dx.doi.org/10.1021/acsami.6b14837DOI Listing
January 2017

Efficient second-harmonic imaging of collagen in histological slides using Bessel beam excitation.

Sci Rep 2016 07 20;6:29863. Epub 2016 Jul 20.

Laboratory for optics and biosciences, Ecole polytechnique, CNRS, INSERM, Université Paris-Saclay, 91128 Palaiseau cedex, France.

Second-harmonic generation (SHG) is the most specific label-free indicator of collagen accumulation in widespread pathologies such as fibrosis, and SHG-based measurements hold important potential for biomedical analyses. However, efficient collagen SHG scoring in histological slides is hampered by the limited depth-of-field of usual nonlinear microscopes relying on focused Gaussian beam excitation. In this work we analyze theoretically and experimentally the use of Bessel beam excitation to address this issue. Focused Bessel beams can provide an axially extended excitation volume for nonlinear microscopy while preserving lateral resolution. We show that shaping the focal volume has consequences on signal level and scattering directionality in the case of coherent signals (such as SHG) which significantly differ from the case of incoherent signals (two-photon excited fluorescence, 2PEF). We demonstrate extended-depth SHG-2PEF imaging of fibrotic mouse kidney histological slides. Finally, we show that Bessel beam excitation combined with spatial filtering of the harmonic light in wave vector space can be used to probe collagen accumulation more efficiently than the usual Gaussian excitation scheme. These results open the way to SHG-based histological diagnoses.
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http://dx.doi.org/10.1038/srep29863DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4951755PMC
July 2016

Luminescent nanoparticle trapping with far-field optical fiber-tip tweezers.

Nanoscale 2016 Mar;8(9):5334-42

Univ. Grenoble Alpes, Inst NEEL, 38000 Grenoble, France. and CNRS, Inst NEEL, 38000 Grenoble, France.

We report stable and reproducible trapping of luminescent dielectric YAG:Ce(3+) nanoparticles with sizes down to 60 nm using far-field dual fiber tip optical tweezers. The particles are synthesized by a specific glycothermal route followed by an original protected annealing step, resulting in significantly enhanced photostability. The tweezers properties are analyzed by studying the trapped particles residual Brownian motion using video or reflected signal records. The trapping potential is harmonic in the transverse direction to the fiber axis, but reveals interference fringes in the axial direction. Large trapping stiffness of 35 and 2 pN μm(-1) W(-1) is measured for a fiber tip-to-tip distance of 3 μm and 300 nm and 60 nm particles, respectively. The forces acting on the nanoparticles are discussed within the dipolar approximation (gradient and scattering force contributions) or exact calculations using the Maxwell Stress Tensor formalism. Prospects for trapping even smaller particles are discussed.
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http://dx.doi.org/10.1039/c5nr07727cDOI Listing
March 2016

Pressure Control of Cuprophilic Interactions in a Luminescent Mechanochromic Copper Cluster.

Inorg Chem 2015 Oct 29;54(20):9821-5. Epub 2015 Sep 29.

Laboratoire de Physique de la Matière Condensée (PMC), CNRS, Ecole Polytechnique , 91128 Palaiseau Cedex, France.

For the development of applications based on mechanochromic luminescent materials, a comprehensive study of the mechanism responsible for the emission changes is required. We report the study of a mechanochromic copper iodide cluster under hydrostatic pressure, which allows control of crystal packing via modification of the intermolecular interactions. In situ single-crystal powder X-ray diffraction analysis and emission measurements under pressure permit one to establish a direct correlation between the molecular structure and luminescence properties and, in particular, to demonstrate that cuprophilic interactions are responsible for the stimuli-responsive luminescence properties of such multinuclear coordination compounds.
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http://dx.doi.org/10.1021/acs.inorgchem.5b01546DOI Listing
October 2015

Electric field induced birefringence in non-aqueous dispersions of mineral nanorods.

Soft Matter 2015 Sep;11(33):6595-603

Centre de Recherche Paul-Pascal, CNRS - Université de Bordeaux, 115 Avenue Schweitzer, 33600 Pessac, France.

Lanthanum phosphate (LaPO4) nanorods dispersed in the non-aqueous solvent of ethylene glycol form a system exhibiting large intrinsic birefringence, high colloidal stability and the ability to self-organize into liquid crystalline phases. In order to probe the electro-optical response of these rod dispersions we study here the electric-field-induced birefringence, also called Kerr effect, for a concentrated isotropic liquid state with an in-plane a.c. sinusoidal electric field, in conditions of directly applied (electrodes in contact with the sample) or externally applied (electrodes outside the sample cell) fields. Performing an analysis of the electric polarizability of our rod-like particles in the framework of Maxwell-Wagner-O'Konski theory, we account quantitatively for the coupling between the induced steady-state birefringence and the electric field as a function of the voltage frequency for both sample geometries. The switching time of this non-aqueous transparent system has been measured, and combined with its high Kerr coefficients and its features of optically isotropic "off-state" and athermal phase behavior, this represents a promising proof-of-concept for the integration of anisotropic nanoparticle suspensions into a new generation of electro-optical devices.
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http://dx.doi.org/10.1039/c5sm01427aDOI Listing
September 2015

Geometry flexibility of copper iodide clusters: variability in luminescence thermochromism.

Inorg Chem 2015 May 10;54(9):4483-94. Epub 2015 Apr 10.

⊗Science et Technologies, Université Lille, F-59000 Lille, France.

An original copper(I) iodide cluster of novel geometry obtained by using a diphosphine ligand is reported and is formulated [Cu6I6(PPh2(CH2)3PPh2)3] (1). Interestingly, this sort of "eared cubane" cluster based on the [Cu6I6] inorganic core can be viewed as a combination of the two known [Cu4I4] units, namely, the cubane and the open-chair isomeric geometries. The synthesis, structural and photophysical characterisations, as well as theoretical study of this copper iodide along with the derived cubane (3) and open-chair (2) [Cu4I4(PPh3)4] forms, were investigated. A new polymorph of the cubane [Cu4I4(PPh3)4] cluster is indeed presented (3). The structural differences of the clusters were analyzed by solid-state nuclear magnetic resonance spectroscopy. Luminescence properties of the three clusters were studied in detail as a function of the temperature showing reversible luminescence thermochromism for 1 with an intense orange emission at room temperature. This behavior presents different feature compared to the cubane cluster and completely contrasts with the open isomer, which is almost nonemissive at room temperature. Indeed, the thermochromism of 1 differs by a concomitant increase of the two emission bands by lowering the temperature, in contrast to an equilibrium phenomenon for 3. The luminescence properties of 2 are very different by exhibiting only one single band when cooled. To rationalize the different optical properties observed, density functional theory calculations were performed for the three clusters giving straightforward explanation for the different luminescence thermochromism observed, which is attributed to different contributions of the ligands to the molecular orbitals. Comparison of 3 with its [Cu4I4(PPh3)4] cubane polymorphs highlights the sensibility of the emission properties to the cuprophilic interactions.
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http://dx.doi.org/10.1021/acs.inorgchem.5b00321DOI Listing
May 2015

Mechanochromic luminescence of copper iodide clusters.

Chemistry 2015 Apr 5;21(15):5892-7. Epub 2015 Mar 5.

Laboratoire de Physique de la Matière Condensée, UMR 7643, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France).

Luminescent mechanochromic materials are particularly appealing for the development of stimuli-responsive materials. Establishing the mechanism responsible for the mechanochromism is always an issue owing to the difficulty in characterizing the ground phase. Herein, the study of real crystalline polymorphs of a mechanochromic and thermochromic luminescent copper iodide cluster permits us to clearly establish the mechanism involved. The local disruption of the crystal packing induces changes in the cluster geometry and in particular the modification of the cuprophilic interactions, which consequently modify the emissive states. This study constitutes a step further toward the understanding of the mechanism involved in the mechanochromic luminescent properties of multimetallic coordination complexes.
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http://dx.doi.org/10.1002/chem.201500251DOI Listing
April 2015

Nanoparticulate coatings with efficient up-conversion properties.

ACS Appl Mater Interfaces 2014 Dec 3;6(24):22483-9. Epub 2014 Dec 3.

Laboratoire de Physique de la Matière Condensée, Ecole Polytechnique , CNRS UMR 7643 Route de Saclay, 91 128 Palaiseau Cedex, France.

Nanoparticulate films with high up-conversion emission (UC) properties were prepared by spray-deposition of nanometer-sized YVO4:Yb,Er particles. The optical properties of YVO4:Yb,Er were optimized upon annealing before the film deposition in order to get the highest possible UC signal in the considered type of system. Thanks to a simple model and some time-resolved spectroscopic investigations, the contribution of the scattering to the UC signal could be separated from the intrinsic properties (crystallinity, surface defects) of the material. The films obtained by this technique present the advantages of having both high UC and good transparency.
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http://dx.doi.org/10.1021/am5065377DOI Listing
December 2014

Single YVO4:Eu nanoparticle emission spectra using direct Eu3+ ion excitation with a sum-frequency 465-nm solid-state laser.

Opt Express 2014 Aug;22(17):20542-50

We report emission spectrum measurements on single YxEu(1-x)VO4 nanoparticles. The inhomogeneous widths of the emission peaks are identical for single nanoparticles and for ensembles of nanoparticles, while being broader than those of the bulk material. This indicates that individual nanoparticles are identical in terms of the distribution of different local Eu3+ sites due to crystalline defects and confirms their usability as identical, single-particle oxidant biosensors. Moreover, we report a 465 nm solid-state laser based on sum-frequency mixing that provides a compact, efficient solution for direct Eu3+ excitation of these nanoparticles. Both these two aspects should broaden the scope of Eu-doped nanoparticle applications.
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http://dx.doi.org/10.1364/OE.22.020542DOI Listing
August 2014

Multifunctional rare-Earth vanadate nanoparticles: luminescent labels, oxidant sensors, and MRI contrast agents.

ACS Nano 2014 Nov 20;8(11):11126-37. Epub 2014 Oct 20.

Laboratoire d'Optique et Biosciences, Ecole Polytechnique , CNRS UMR 7645-INSERM U696, 91128 Palaiseau Cedex, France.

Collecting information on multiple pathophysiological parameters is essential for understanding complex pathologies, especially given the large interindividual variability. We report here multifunctional nanoparticles which are luminescent probes, oxidant sensors, and contrast agents in magnetic resonance imaging (MRI). Eu(3+) ions in an yttrium vanadate matrix have been demonstrated to emit strong, nonblinking, and stable luminescence. Time- and space-resolved optical oxidant detection is feasible after reversible photoreduction of Eu(3+) to Eu(2+) and reoxidation by oxidants, such as H2O2, leading to a modulation of the luminescence emission. The incorporation of paramagnetic Gd(3+) confers in addition proton relaxation enhancing properties to the system. We synthesized and characterized nanoparticles of either 5 or 30 nm diameter with compositions of GdVO4 and Gd0.6Eu0.4VO4. These particles retain the luminescence and oxidant detection properties of YVO4:Eu. Moreover, the proton relaxivity of GdVO4 and Gd0.6Eu0.4VO4 nanoparticles of 5 nm diameter is higher than that of the commercial Gd(3+) chelate compound Dotarem at 20 MHz. Nuclear magnetic resonance dispersion spectroscopy showed a relaxivity increase above 10 MHz. Complexometric titration indicated that rare-earth leaching is negligible. The 5 nm nanoparticles injected in mice were observed with MRI to concentrate in the liver and the bladder after 30 min. Thus, these multifunctional rare-earth vanadate nanoparticles pave the way for simultaneous optical and magnetic resonance detection, in particular, for in vivo localization evolution and reactive oxygen species detection in a broad range of physiological and pathophysiological conditions.
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http://dx.doi.org/10.1021/nn504170xDOI Listing
November 2014