Doru Constantin

Doru Constantin
French National Centre for Scientific Research | CNRS · Institut Charles Sadron

PhD

About

102
Publications
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Introduction
I am a soft matter physicist, currently employed as permanent researcher with the CNRS (French research institution) in Strasbourg.

Publications

Publications (102)
Article
Rational nanoparticle design is one of the main goals of materials science, but it can only be achieved via a thorough understanding of the growth process and of the respective roles of the molecular species involved. We demonstrate that a combination of complementary techniques can yield novel information with respect to their individual contribut...
Article
Full-text available
We study the assembly kinetics of surfactant-stabilized gold nanoparticles in the presence of sulfate ions. The reaction proceeds in two steps: very rapid (a few minutes) formation of amorphous aggregates, followed by slow reordering (over several hours). The latter process is the only one detectable via absorbance spectroscopy and results in the f...
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Organizing nanoparticles (NPs) into periodic structures is a central goal in materials science. Despite progress in the last decades, it is still challenging to produce macroscopic assemblies reliably. In this work, the analysis of the pervaporation‐induced organization of gold octahedra into supercrystals within microfluidic channels using a combi...
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Pentagonal packing is a long‐standing issue and a rich mathematical topic, brought to the fore by recent progress in nanoparticle design. Gold pentagonal bipyramids combine five‐fold symmetry and anisotropy and their section varies along the length. In this work, we obtain colloidal supercrystals of pentagonal gold bipyramids in a compact arrangeme...
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Bimetallic Au/Ag core–shell cuboid nanoparticles (NPs) exhibit a complex plasmonic response dominated by a dipolar longitudinal mode and higher-order transverse modes in the near-UV, which may be exploited for a range of applications. In this paper, we take advantage of the strong signature of these modes in the NP ultrafast transient optical respo...
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We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the num...
Article
New collective optical properties emerge nowadays with organized and oriented arrays of close packed semiconducting and metallic nanoparticles (NPs). However, it is challenging to obtain NP assemblies everywhere similar on...
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The two main classes of liquid-crystal (LC) phases of rodlike molecules are nematics, where the rods align in the same direction (the nematic director n), and smectics, where the rods not only are aligned but also form layers. The electro-optic effects in LC devices that are a backbone in today’s display industry mainly use the Fréedericksz transit...
Article
Many soft matter systems are composed of roughly spherical objects that can self-assemble in ordered structures. Unlike hard spheres, at high volume fraction these soft spheres adapt their shape to the local geometrical constraints and the question of space filling needs to be entirely revisited. Hydrophobically coated gold nanocrystals self-assemb...
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Recently developed, nanoscale metal-organic frameworks (nanoMOFs) functionalized with versatile coatings are drawing special attention in the nanomedicine field. Here we show the preparation of core–shell MIL-100(Al) nanoMOFs for the delivery of the anticancer drug doxorubicin (DOX). DOX was efficiently incorporated in the MOFs and was released in...
Preprint
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Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and near-infrared spectral ranges and have many applications. Modifying the size, shape, and composition of the nanoparticles changes the number of modes and their properties. The characteristics of these modes are transiently affected when illuminating the na...
Article
Despite their promising use in electrochemical and electrokinetic devices, ionic-liquid-based electrolytes often exhibit complex behavior arising from a subtle interplay of their structure and dynamics. Here, we report a joint experimental and molecular simulation study of such electrolytes obtained by mixing 1-butyl 3-methylimidazolium tetrafluoro...
Article
Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and near‐infrared spectral ranges and have many applications. Modifying the size, shape, and composition of the nanoparticles changes the number of modes and their properties. The characteristics of these modes are transiently affected when illuminating the na...
Article
Correction for ‘Solution self-assembly of plasmonic Janus nanoparticles’ by Nicolò Castro et al. , Soft Matter , 2016, 12 , 9666–9673, DOI: 10.1039/C6SM01632D.
Article
We study by synchrotron-based time-resolved small angle X-ray scattering the growth of silver shells on gold nanorods in the presence of hexadecyltrimethylammonium chloride (CTAC) as a function of the silver/gold molar ratio K. For all but the highest K values, the silver precursor is completely converted to the solid phase. The growth rate of the...
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Accurately measuring the shape, structure and concentration of nanoparticles (NPs) is a crucial step towards understanding their formation and a prerequisite for any applications. While determining these parameters for single-metal NPs is by now rather routine, reliably characterizing bimetallic NPs is still a challenge. Using four complementary te...
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Revealing the Dynamics of Functional Nanomaterials in Their Formation and Application Media with Liquid and Gas-phase TEM - Damien Alloyeau, Abdelali Khelfa, Kinan Aliyah, Adrian Chmielewski, Jun Meng, Hakim Amara, Hazar Guesmi, Jaysen Nelayah, guillaume Wang, Cyrille Hamon, Doru Constantin, Christian Ricolleau
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Grazing incidence X-ray diffraction (GIXD) studies of monolayers of biomolecules at an air–water interface give quantitative information of in-plane packing, coherence length of crystalline domains, etc. Rheo-GIXD measurements can reveal quantitative changes in the nanocrystalline domains of a monolayer under shear. Here, we report GIXD studies of...
Preprint
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In 1993, Nallet, Laversanne and Roux put forward a simplified model for the intensity scattered by lamellar phases, which was nonetheless very successfully used in fitting experimental results, especially those obtained with powder systems. I argue that the success as well as the simple expression of the model result from an approximate integration...
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Liquid Crystal (LC) topological defects have been shown to trap nanoparticles (NPs) in the defect cores. The LC topological defects may thus be used as a matrix for new kinds of NP organizations templated by the defect geometry. We here study composites of LC smectic dislocations and gold NPs. Straight NP chains parallel to the dislocations are obt...
Article
In this article, we show how advanced hierarchical structures of topological defects in the so-called smectic oily streaks can be used to sequentially transfer their geometrical features to gold nanospheres. We use two kinds of topological defects, 1D dislocations and 2D ribbon-like topological defects. The large trapping efficiency of the smectic...
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Engineering plasmonic hot-spots is essential for applications of plasmonic nanoparticles. A particularly appealing route is to weld plasmonic nanoparticles together to form more complex structures sustaining plasmons with symmetries targeted to given applications. However, the control of the welding and subsequent hotspot characteristic is still ch...
Preprint
p>Plasmonic particles can be welded together, but controlling the metallurgy of the hotspots is a challenge in colloidal chemistry. In this paper, we demonstrate an original method that connects gold particles to their neighbors by another metal of choice. To achieve this goal, we first assemble gold bipyramids in a tip-to-tip configuration, yieldi...
Preprint
Rational nanoparticle design is one of the main goals of materials science, but it can only be achieved via a thorough understanding of the growth process and of the respective roles of the molecular species involved. We demonstrate that a combination of complementary techniques can yield novel information with respect to their individual contribut...
Article
Two dimensional ultra thin CdSe nanoplatelets have attracted a large interest due to their optical properties but their formation mechanism is not well understood. Several different mechanisms have been proposed: confined growth in a surfactant mesophase acting as a template, anisotropic ripening of small seeds into 2D nanoplatelets or continuous a...
Preprint
Full-text available
Grazing Incidence X-ray Diffraction (GIXD) studies of monolayers of biomolecules at the air-water interface give quantitative information of in-plane packing, coherence lengths of the ordered (diffracting) domains and orientation of hydrocarbon chains of the model membranes. Rheo-GIXD measurements revel quantitative changes in the monolayer under s...
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Nanosized metal-organic frameworks (nanoMOFs) MIL-100(Fe) are highly porous and biodegradable materials that have emerged as promising drug nanocarriers. A challenging issue concerns their surface functionalization in order to evade the immune system and to provide molecular recognition ability, so that they can be used for specific targeting. A co...
Article
Within the framework of a discrete Gaussian model, we present analytical results for the interaction induced by a lamellar phase between small embedded colloidal particles. We consider the two limits of particles strongly adherent to the adjacent membranes and of particles impenetrable to the membranes. Our approach takes into account the finite si...
Article
Viral capsid proteins have the remarkable ability to self-assemble around a cargo core, whether their genome, a polyelectrolyte or an inorganic nanoparticle. Although the equilibrium properties of gold nanoparticles encapsulated in viral capsids have been broadly investigated, little is known about the kinetic pathways leading to their assembly. Th...
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Tailoring the crystal structure of plasmonic nanoparticle superlattices is a crucial step in controlling the collective physical response of these nanostructured materials. Various strategies can achieve this goal for isotropic nanoparticles, but few of them have been successful with anisotropic building blocks. In this work we use hybrid particles...
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The survival of viruses partly relies on their ability to self-assemble inside host cells. Although coarse-grained simulations have identified different pathways leading to assembled virions from their components, experimental evidence is severely lacking. Here, we use time-resolved small-angle X-ray scattering to uncover the nonequilibrium self-as...
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Using synchrotron-based small angle x-ray scattering, we study rigid \textit{fd} viruses assembled into isolated monolayers from mixtures with a non-absorbing polymer, which acts as osmotic agent. As the polymer concentration increases we observe a direct liquid to crystal transition, without an intermediate hexatic phase, in contrast with many oth...
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The phase diagram of colloidal suspensions of electrically charged nanosheets, such as clays, despite their many industrial uses, is not yet understood either experimentally or theoretically. When the nanosheet diameter is very large (∼100 nm to 1 µm), it is quite challenging to distinguish the lamellar liquid-crystalline phase from a nematic phase...
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The activity of cell membrane inclusions (such as ion channels) is influenced by the host lipid membrane, to which they are elastically coupled. This coupling concerns the hydrophobic thickness of the bilayer (imposed by the length of the channel, as per the hydrophobic matching principle) but also its slope at the boundary of the inclusion. Howeve...
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We study the local effect of the antimicrobial peptide Gramicidin A on bilayers composed of lipids or surfactants using nuclear magnetic resonance spectroscopy and wide-angle X-ray scattering, techniques that probe the orientational and positional order of the alkyl chains, respectively. The two types of order vary with temperature and peptide conc...
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Interactions mediated by the cell membrane between inclusions, such as membrane proteins or antimicrobial peptides, play important roles in their biological activity. They also constitute a fascinating challenge for physicists, since they test the boundaries of our understanding of self-assembled lipid membranes, which are remarkable examples of tw...
Article
We designed a nanocomposite consisting of CdSe nanoplatelets dispersed in the form of short stacks in the polybutadiene domains of a polystyrene–polybutadiene–polystyrene (SBS) thermoplastic elastomer matrix. Under strain, the material displays reversible, macroscopic anisotropic properties, e.g. the fluorescence signal. We present here a structura...
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Ionic Liquids (ILs) are a specific class of molecular electrolytes characterized by the total absence of co-solvent. Due to their remarkable chemical and electrochemical stability, they are prime candidates for the development of safe and sustainable energy storage systems. The competition between electrostatic and van der Waals interactions leads...
Article
Janus nanoparticles bearing two different properties on a single particle are amenable to self-assembly into higher-order structures via their directional interaction. We show that gold/silica Janus nanoparticles self-assemble in solution into clusters resembling colloidal micelles upon addition of a hydrophobic thiol which provides them with a sur...
Article
Viruses are astonishing edifices in which hundreds of molecular building blocks fit into the final structure with pinpoint accuracy. We established a robust kinetic model accounting for the in vitro self-assembly of a capsid shell derived from an icosahedral plant virus by using time-resolved small-angle X-ray scattering (TR-SAXS) data at high spat...
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When probed at the macroscopic scale, Ionic Liquids (ILs) behave as highly dissociated (i.e. strong) electrolytes while, at the molecular scale, they show clear characteristics of weak ionic solutions. The multi-scale analysis we report in this paper reconciles these apparently at odds behaviors. We investigate by quasi-elastic neutron scattering (...
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Analytical or semi-analytical expressions are provided for the small-angle scattering of colloidal objects that can be described as curved plates. These models could help to characterize a variety of inorganic or biological systems.
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We compare the light extinction spectra of elongated gold nanoparticles with different shapes (cylinder, spherocylinder and ellipsoid) and sizes of 10 to 100nm. We argue that the equivalence of the various moments of mass distribution is the natural comparison criterion —rather than the length-to-diameter (aspect) ratio generally used in the litera...
Article
Viral capsids derived from an icosahedral plant virus widely used in physical and nanotechnological investigations were fully dissociated into dimers by a rapid change of pH. The process was probed in vitro at high spatiotemporal resolution by time-resolved small-angle X-ray scattering using a high brilliance synchrotron source. A powerful custom-m...
Article
Understanding the formation mechanism of colloidal nanocrystals is of paramount importance in order to design new nanostructures and synthesize them in a predictive fashion. However, reliable data on the pathways leading from molecular precursors to nanocrystals are not available yet. We used synchrotron-based time-resolved in situ small and wide-a...
Article
By dispersing semi-conducting CdSe nanoplatelets within a styrene-butadiene-styrene block copolymer matrix we form homogeneous fluorescent hybrid films. Reversible orientation control of the nanoplatelets is simply achieved through stretching the film, leading to tuneable fluorescence anisotropy. Such adjustable polarization effects are useful for...
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Full-text available
UV-Vis absorption spectroscopy is frequently used to characterize the size and shape of gold nanoparticles. We present a full-spectrum model that yields reliable results for the commonly encountered case of mixtures of spheres and rods in varying proportions. We determine the volume fractions of the two populations, the aspect ratio distribution of...
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Three mesostructured silica-type carriers, MCM-41 and MCM-41 functionalized by a postsynthesis grafting procedure with hydrophilic aminopropyl groups (MCM-APTES) and hydrophobic vinyl moieties (MCM-VTES), respectively, were investigated in order to elaborate drug delivery systems (DDS) for irinotecan molecules. All studied drug delivery systems exh...
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Gold nanorods have unique optical properties, which make them promising candidates for building nano-structured materials using a "bottom-up" strategy. We formulate stable bulk materials with anisotropic optical properties by inserting gold and iron oxide nanorods within a lamellar mesophase. Quantitative measurements of the order parameter by mode...
Article
The development of nanostructured hybrid systems is a flourishing area of research, which brings together chemistry, physics and materials science. These systems are composed of nanoparticles with interesting properties (e.g. optical, magnetic, catalytic) dispersed within an organic matrix. Control of both the position and orientation of the partic...
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We report a hybrid mesophase consisting of magnetic nanorods confined between the non-ionic surfactant bilayers of a lamellar phase. The magnetic field-induced ordering of the nanorods was measured experimentally and modeled by a two-dimensional Onsager theory including the third virial coefficient. The nanorods are strongly confined in layers, wit...
Article
For many important applications, the performance of (polymer - anisotropic particle) nanocomposite materials strongly depends on the orientation of the nanoparticles. Using the very peculiar magnetic properties of goethite (-FeOOH) nanorods, we produced (goethite - PHEMA) nanocomposites in which the alignment direction and the level of orientation...
Article
In modern medicine, effective protein therapy is a major challenge to which a significant contribution can be expected from nanoscience through the development of novel delivery systems. Here we present the effect of the amine content of nanoparticles based on PEGylated chitosan Bombyx mori (PEG-O-ChsBm) copolymers on the entrapment of molecules in...
Article
Gold nanorods have unique optical properties, which make them promising candidates for building nano-structured materials using a "bottom-up" strategy. We formulate stable bulk materials with anisotropic optical properties by inserting gold and iron oxide nanorods within a lamellar mesophase. Quantitative measurements of the order parameter by mode...
Article
Silver and gold nanoparticle superlattices with a layered structure were obtained via grafting of mesogenic molecules onto a metallic cluster surface. For the Ag superstructures unusual orientational order of the mesogenic ligands and anisotropy of the assembly afforded tunable plasmonic properties.
Article
The self-assembly kinetics for a norovirus capsid protein were probed by time-resolved small-angle X-ray scattering and then analyzed by singular value decomposition and global fitting. Only three species contribute to the total scattering intensities: dimers, intermediates comprising some 11 dimers, and icosahedral T = 3 capsids made up of 90 dime...
Article
Transmembrane proteins that have a hydrophobic mismatch with the membrane induce membrane thickness deformations at the nanoscale [1].We put forward a modification to continuum elastic models describing membrane thickness deformations [2]. We show that contributions involving the gradient (and the Laplacian) of the area per lipid are significant an...