Laurent Servant

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (58)135.22 Total impact

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    ABSTRACT: Probing specific RNA sequences is an issue of major significance for which fluorescence dominates most of the investigation strategies and relies heavily on the use of specific labels. In this paper, we report the detection by SERS (surface-enhanced Raman scattering) of unlabeled model purified oligonucleotides RNA polyadenosine (5′-AAAAAAAAAA-3′) and polycytosine (5′-CCCCCCCCCC-3′) combining silver nanoparticles as enhancing surfaces with microfluidic platforms to control species movement and the aggregation state of the nanoparticles, which is critical for the sensitivity. Two types of microfluidic platforms have been evaluated and compared: one based on laminar streams and the other involving flowing droplets acting as chemical reactors. Both platforms provide homogeneous and controlled mixing conditions of nanoparticles with oligonucleotides: laminar streams induce mixing driven by diffusion, whereas droplets permit fast and efficient mixing through internal fluid recirculation and prevent channel clogging by nanoparticles. We demonstrate that in both cases, the bases can be detected selectively. In the droplet microfluidic system, the Raman maximum enhancement is localized in the center of the droplet and observed after a certain period of mixing time that appears specific for each base, after droplet formation. It appears to be a highly promising approach for probing unlabeled nucleotides using SERS.
    The Journal of Physical Chemistry C. 06/2014; 118(25):13965–13971.
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    ABSTRACT: Double-stranded (ds) DNA of a λ-phage virus are combed on octadecyltrichlorosilane (OTS)-modified borosilicate glass substrates and investigated by means of tip-enhanced Raman spectroscopy (TERS) using tips coated with an Ag/Au bilayer. Owing to an enhancement factor higher than 6 ×102 and a lateral spatial resolution better than 9 nm (which is below the size of the tip apex radius), cross-sections of nanowire-shaped thin DNA bundles can be spatially resolved. TER spectra reveal vibrational modes typical of DNA nucleobases and backbone, as confirmed by confocal Raman measurements carried out on dense stacks of DNA strands. While the TER signature of nucleobases is congruent with observations in single-stranded (ss) DNA, additional modes tied to the DNA backbone can be discerned in ds DNA. TERS enables ss and ds DNA samples to be distinguished from each other and hence can be exploited for the detection of DNA hybridization. Moreover, no TER contribution of the OTS layer appears, suggesting that functionalized DNA strands could be studied without spectral perturbation from the substrate. This work paves the way toward the nanoscale spectral study of organized DNA-based nanostructures.
    The Journal of Physical Chemistry C 01/2014; 118:1174-1181. · 4.84 Impact Factor
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    ABSTRACT: In the aim of understanding the relations between the spectroscopic properties of blue phosphor BaMgAl10O17:Eu2+ and its crystal structure, microstructure and chemical composition, three fluoride fluxes (LiF, MgF2 and NH4F) have been added before final thermal treatment and their effect analyzed. LiF changes the polycrystalline and spherical grains into hexagonal platelets without significant cations exchange and improves the luminescence. NH4F and MgF2 only have a limited effect, the former because of its low point of decomposition, the latter because of the formation of spurious MgAl2O4 that reduces the luminescence. In a general way, re-crystallization results in variations of the dopant distribution between the three host sites of the structure. Chromaticity is only faintly affected, but important variations of the absorption and excitation spectra are observed, allowing a strong increase of photoluminescence intensity under near-UV excitation.
    Materials Research Bulletin. 08/2013; 48(8):2960–2968.
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    ABSTRACT: Thermal degradation of blue phosphor BAM:Eu2 + under air is investigated using XPS, XRD, EPR and photoluminescence (PL) in order to analyze the loss of intensity in terms of modifications of the dopant distribution in the crystal cell and between crystal bulk and surface. This study reveals the key role played by oxidation-driven 2D diffusion of europium and barium, that results in important concentration gradients and makes degradation strongly dependent on both microstructure and cooling speed. Also based upon cation mobility, a possible regeneration effect is evidenced at moderate temperature. Flux treatments, known to increase the intensity of photoluminescence, also appear to reduce thermal degradation by lowering specific surface; they also enhance the regeneration process by forming extended single-crystal domains conducive to cation diffusion.
    Solid State Ionics 01/2013; 253:32–38. · 2.05 Impact Factor
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    ABSTRACT: The role of carbon dioxide on the climate change and the depletion of fossil resources prompt to develop new and original approaches to limit CO2 emissions through its capture or its utilization. The simplest idea, before any recycling of CO2, consists in fixing it in a reversible way at the surface of solid materials. This paper describes the research made by a consortium of four laboratories in order to characterize the parameters of CO2 adsorption on various samples (rare earth oxides, carbon materials, grafted silica) and guide the search for new performing materials. Samples are tested via in situ and coupled experiments (thermometry, infrared spectroscopy), mimicking the capture of CO2 by an adsorption column. The access to a temperature field by infrared thermometry will allow the total analysis of industrial process mock-up.
    L'Actualité chimique 01/2013; 371-372:40-46. · 0.09 Impact Factor
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    ABSTRACT: In bulk heterojunction (BHJ) polymeric organic solar cells (OSCs), the use of processing additives in the material formulation has emerged as a promising, cost-effective, and widely applicable method for optimizing the phase separation between the donor (D) and acceptor (A) materials, thus increasing their efficiency. So far, however, there has been no systematic approach for identifying suitable processing additives for a given D:A system. A method based on the Hansen solubility parameters (HSPs) is proposed for guiding the selection of processing additives for a given D:A combination. The method is applied to the archetypical poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) system. The HSPs of these materials are determined and used to define a set of numerical criteria that need to be satisfied by a processing additive in order for it to be effective in realizing a higher efficiency OSC. Applying the selection criteria results in the identification of three novel processing additives. OSCs made of these formulations demonstrate an increase in their short-circuit current density (JSC) and power conversion efficiency (PCE). These results demonstrate the efficiency of these novel processing additives and show that the HSPs represent a useful tool to determine and explore new types of processing additives for BHJ-OSCs.
    Advanced Energy Materials. 01/2013;
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    ABSTRACT: Nanoporous SnO(2)-ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, the synthesis of nanosized SnO(2) particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO(2) particles with zinc acetate followed by calcination at 500 °C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption analyses, transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy. The SnO(2)-ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO(2) nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV-visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO(2)-ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO(2), that is, 3.7 eV, and ZnO, that is, 3.2 eV, analogues. The energy band diagram of the SnO(2)-ZnO heterostructure was directly determined by combining XPS and the energy band gap values. The valence band and conduction band offsets were calculated to be 0.70 ± 0.05 eV and 0.20 ± 0.05 eV, respectively, which revealed a type-II band alignment. Moreover, the heterostructure SnO(2)-ZnO photocatalyst showed much higher photocatalytic activities for the degradation of methylene blue than those of individual SnO(2) and ZnO nanomaterials. This behavior was rationalized in terms of better charge separation and the suppression of charge recombination in the SnO(2)-ZnO photocatalyst because of the energy difference between the conduction band edges of SnO(2) and ZnO as evidenced by the band alignment determination. Finally, this mesoporous SnO(2)-ZnO heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications.
    Inorganic Chemistry 06/2012; 51(14):7764-73. · 4.59 Impact Factor
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    ABSTRACT: Surface-enhanced Raman scattering (SERS)-based microfluidic platforms are investigated to optimize the detection of biomolecules using silver nanoparticles. The method is established using pefloxacin (an antibacterial agent) as a probe. We first monitor the continuous SERS signal of a 10–5 M pefloxacin solution diffusing continuously into a silver nanoparticle stream across the shared interface separating the two-phase, segmented microfluidic laminar flow system. Diffusion of the pefloxacin adsorbate begins immediately after the two streams merge, generating silver aggregates and producing a huge enhancement of the Raman bands of pefloxacin. We show that the evolution of the SERS signal presents a diffusion-like behavior, whose dynamics can be easily monitored as the signal measured in the flow-wise direction is proportional to the reaction time. Finally, we demonstrate that it is possible to optimize SERS intensity spectra by adding a controlled amounts of chloride ions through a side channel to control silver particles aggregation and further enhance Raman scattering.
    The Journal of Physical Chemistry C. 02/2012; 116(9):5327–5332.
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    ABSTRACT: Ionic liquids based on three‐membered ring aziridinium cations have been synthesized for the first time using a straightforward synthetic route. N‐butyl‐N‐methylaziridinium bis(trifluoromethanesulfonyl)imide, N‐propyl‐N‐ethylaziridinium bis(trifluoromethanesulfonyl)imide, N‐butyl‐N‐[2‐(2‐methoxyethoxy)ethyl]aziridinium bis(trifluoromethanesulfonyl)imide, N‐butyl‐N‐methylaziridinium dicyanamide, and N‐butyl‐N‐ethylaziridinium dicyanamide were thus obtained in good yields and satisfactory purity and fully characterized.
    Journal of Heterocyclic Chemistry 01/2012; 49(3). · 1.22 Impact Factor
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    ABSTRACT: Surface-Enhanced Raman Spectroscopy (SERS) was performed to detect label-free RNA. We defined conditions which make it possible to probe the four bases of RNA, in single strands of polyadenosine (pA), polyuridine (pU), polycytosine (pC) and polyguanosine (pG). We therefore present below a quantitative analysis of mixtures of non-hybridized single strands, based on the deconvolution of the SERS mixture spectrum into the relative contributions of the SERS spectra of each constituent.
    Chemical Communications 07/2011; 47(26):7425-7. · 6.38 Impact Factor
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    ABSTRACT: Unprecedented stable hybrid materials with cyclopentadienyl-titanium bonds have been obtained from the hydrolysis of suitable precursors. Their inorganic network is not fully condensed and they show variable short-range self-organizations, the type of which depends on the shape of the ligands.
    Chemical Communications 03/2011; 47(17):5001-3. · 6.38 Impact Factor
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    ABSTRACT: Many in vitro studies have pointed out the interaction between amyloids and membranes, and their potential involvement in amyloid toxicity. In a previous study, we generated a yeast toxic mutant (M8) of the harmless model amyloid protein HET-s((218-289)). In this study, we compared the self-assembling process of the nontoxic wild-type (WT) and toxic (M8) protein at the air-water interface and in interaction with various phospholipid monolayers (DOPE, DOPC, DOPI, DOPS and DOPG). We first demonstrate using ellipsometry measurements and polarization-modulated infrared reflection absorption spectroscopy (PMIRRAS) that the air-water interface promotes and modifies the assembly of WT since an amyloid-like film was instantaneously formed at the interface with an antiparallel β-sheet structuration instead of the parallel β-sheet commonly observed for amyloid fibers generated in solution. The toxic mutant (M8) behaves in a similar manner at the air-water interface or in bulk, with a fast self-assembling and an antiparallel β-sheet organization. The transmission electron microscopy (TEM) images established the fibrillous morphology of the protein films formed at the air-water interface. Second, we demonstrate for the first time that the main driving force between this particular fungus amyloid and membrane interaction is based on electrostatic interactions with negatively charged phospholipids (DOPG, DOPI, DOPS). Interestingly, the toxic mutant (M8) clearly induces perturbations of the negatively charged phospholipid monolayers, leading to a massive surface aggregation, whereas the nontoxic (WT) exhibits a slight effect on the membrane models. This study allows concluding that the toxicity of the M8 mutant could be due to its high propensity to interact with membranes.
    Langmuir 03/2011; 27(8):4797-807. · 4.38 Impact Factor
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    ABSTRACT: Accurate chemical and structural characterization of free-standing zinc oxide (ZnO) and hematite (α-Fe2O3) nanorods has been carried out using an AFM/Raman correlative technique under polarized light. ZnO nanorods are found to be wurtzite-type single crystalline objects homogeneous in composition and grown along their principal axis of symmetry. Hematite specimens are rhombohedral corundum-type single crystals grown along a direction orthogonal to their principal axis of symmetry and exhibiting structural disorder. Certain hematite nanorods turn out to be very sensitive to laser heating. These studies reveal the high potential of the coupled AFM/Raman technique to examine the properties of these promising nanomaterials.
    Chemical Physics Letters 01/2011; 514(1):128-133. · 2.15 Impact Factor
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    ABSTRACT: 8th European Biophysics Congress (EBSA), Budapest, Hungary, 23-27 août 2011 Eur. Biophys. J. 40 (1) 94 (Abstract and poster).
    European Biophysics Journal with Biophysics Letters. 01/2011; 40:94-94.
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    ABSTRACT: Lattice dynamics of nickel hydroxide, β-Ni(OH)2, electrode material for current batteries, has been investigated by incoherent inelastic neutron scattering. Results are discussed through comparison with the isostructural and well studied model compound, Mg(OH)2. The zone-center phonon spectra calculated in the frame of the density functional theory showed the important role of the spin–spin interactions in nickel hydroxide. Analysis of the calculated force constant matrix provided some insight into peculiarities of interatomic interactions in these layered compounds. A similar theoretical approach is applied to the investigation of the atomic structure and lattice dynamics of the β-NiOOH phase.
    Solid State Ionics. 01/2010;
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    ABSTRACT: Remote surface enhanced Raman spectroscopy (SERS) imaging of an adsorbed monolayer was demonstrated through a nanostructured array of conical tips inscribed onto the distal face of a 30 cm optical fiber bundle. Despite intense Raman signal from the germanium oxide doped fibers, the Raman signal of an adsorbed monolayer of a reference compound (benzene thiol) was detected in the fingerprint region. This opens up the possibility of local remote imaging through an optical fiber that embeds a SERS active platform.
    Optics Express 12/2009; 17(26):24030-5. · 3.55 Impact Factor
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    ABSTRACT: Raman imaging of a single [110] GaN nanowire using a combination of an atomic force microscope (AFM) and an inverted confocal microscope was investigated. The Raman spectra and associated maps of this single object, the diameter of which was of 200 nm, were collected in both confocal mode and with the interaction of an AFM tip to benefit from local tip enhancement effect. Beyond the pure tip-enhanced Raman scattering (TERS) effect, the setup was developed to integrate a commercial AFM and spectrometer to permit simultaneous topography and vibrational imaging with spatial and spectral resolutions determined by the respective instruments. Data exchange and communication of the Raman spectrometer and the AFM were optimized to display both height and Raman intensity for a set of Z positions at the AFM tip for each (x,y) position on the sample. The experiments were conducted with both a straight tip coated with gold at an excitation of λ = 647 nm and with a tilted tip coated with silver at an excitation wavelength of λ = 514 nm. The TERS signal was observed for a given phonon mode of the [110] nanowire, providing an optical resolution that corresponds to the size of the object. Copyright © 2009 John Wiley & Sons, Ltd.
    Journal of Raman Spectroscopy 08/2009; 40(10):1441 - 1445. · 2.68 Impact Factor
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    ABSTRACT: An optical fiber bundle composed of 6000 individual 3 μm core diameter fibers has been chemically etched to form a regular array of sharp tips, resulting in the confinement of the light reaching the tip apexes of the fibers as demonstrated by near-field optical microscopy. After coating this nanostructure with a gold thin film (30 nm thick), spatially resolved Raman experiments have been performed to detect a benzenethiol monolayer adsorbed on the covering gold film. High intensity Raman spectra were observed and localized at the extremities of the tips, demonstrating a surface enhanced Raman scattering (SERS) effect induced by the strong curvature of the metallized tip apexes. The Raman enhancement factor of the nanostructure has been investigated and an average enhancement factor of 2.7 × 104 was measured. This opens new avenues for the use of such optical fibers for in situ and endoscopic Raman measurements on complex systems.
    Journal of Physical Chemistry C - J PHYS CHEM C. 12/2008; 113(3).
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    ABSTRACT: Raman and Fourier transform infrared (FTIR) spectroscopy investigations were performed on carbon-coated materials differing by the temperature of their thermal treatments (575 and ) and by their electrochemical performance, with that obtained at a higher temperature showing larger reversible capacity and better capacity retention at high rates. Raman spectra gave information on the carbon located at the surface of the particles, which was shown for the two samples to be highly disordered with small in-plane correlation lengths . A UV Raman study has shown that these carbon coatings contain almost no -type carbon hybridization. This study has also highlighted again that the -type -type C ratio cannot be determined straightforwardly from Raman spectra recorded with visible excitation (such as ), and thus that no direct correlation can be done between the Raman band intensity ratio and the -type -type C ratio; a UV Raman study is necessary to get the true information on the -type C contribution. The baseline and absolute intensity of the FTIR spectra were shown to be sensitive to changes in the electronic conductivity of the samples. Furthermore, good crystallinity was maintained for materials upon cycling, showing good reversibility of the lithium deintercalation∕intercalation reaction.
    Journal of The Electrochemical Society. 11/2008; 155(12):A879-A886.
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    ABSTRACT: Nanostructured metallic platforms for Raman enhancement were fabricated using Langmuir-Blodgett and electron beam (e-beam) lithography techniques. The gold platforms were inscribed on thin glass slides with the purpose of using them in a transmission geometry experimental setup under a confocal microscope. The plasmon frequency of the gold nanostructures was determined in the visible-near-infrared range for various pattern sizes prepared by Langmuir-Blodgett transfer and e-beam lithography. The surface Raman enhancement factors were determined for a monolayer of azobenzene molecules adsorbed on gold through thiol bonding and compared for both LB transfer and e-beam samples for nanostructures of comparable geometries.
    Langmuir 10/2008; 24(19):11313-21. · 4.38 Impact Factor

Publication Stats

329 Citations
135.22 Total Impact Points


  • 2003–2014
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 1995–2013
    • University of Bordeaux
      Burdeos, Aquitaine, France
  • 2003–2012
    • Université Bordeaux 1
      • UMR ISM - Institut des Sciences Moléculaires
      Talence, Aquitaine, France
  • 2005–2006
    • Ecole Normale Supérieure de Paris
      • Département de Chimie
      Paris, Ile-de-France, France