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International audience; Controlling the spatial arrangement of plasmonic nanoparticles is of particular interest to utilize inter-particle plasmonic coupling, which allows changing their optical properties. For bottom-up approaches, colloidal nanoparticles are interesting building blocks to generate more complex structures via controlled self-assembly using the destabilization of colloidal particles. For plasmonic noble metal nanoparticles, cationic surfactants, such as CTAB, are widely used in synthesis, both as shaping and stabilizing agents. In such a context, understanding and predicting the colloidal stability of a system solely composed of AuNPs and CTAB is fundamentally crucial. Here, we tried to rationalize the particle behavior by reporting the stability diagrams of colloidal gold nanostructures taking into account parameters such as the size, shape, and CTAB/AuNP concentration. We found that the overall stability was dependent on the shape of the nanoparticles, with the presence of sharp tips being the source of instability. For all morphologies evaluated here, a metastable area was systematically observed, in which the system aggregated in a controlled way while maintaining the colloidal stability. Combining different strategies with the help of transmission electron microscopy, the behavior of the system in the different zones of the diagrams was addressed. Finally, by controlling the experimental conditions with the previously obtained diagrams, we were able to obtain linear structures with a rather good control over the number of particles participating in the assembly while maintaining good colloidal stability..

Aim: To propose a new multimodal imaging agent targeting amyloid-β (Aβ) plaques in Alzheimer’s disease. Materials & methods: A new generation of hybrid contrast agents, based on gadolinium fluoride nanoparticles grafted with a pentameric luminescent-conjugated polythiophene, was designed, extensively characterized and evaluated in animal models of Alzheimer’s disease through MRI, two-photon microscopy and synchrotron x-ray phase-contrast imaging. Results & conclusion: Two different grafting densities of luminescent-conjugated polythiophene were achieved while preserving colloidal stability and fluorescent properties, and without affecting biodistribution. In vivo brain uptake was dependent on the blood–brain barrier status. Nevertheless, multimodal imaging showed successful Aβ targeting in both transgenic mice and Aβ fibril-injected rats.

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The generation of hydrogen peroxide on commercial and synthesized ZnO from different precursors was studied using two model molecules, formic acid (FA) and phenol (Ph), as well as phenolic intermediates, hydroquinone (HQ), benzoquinone (BQ), and catechol (CAT). The samples were characterized using X-ray Diffraction (XRD), Transmission Electronic Microscopy (TEM), RAMAN, and Electron Paramagnetic Resonance (EPR) before evaluating their photocatalytic properties. We found that the improved efficiency is accompanied by a high level of H2O2 production, fewer oxygen vacancies, and that the number of moles of H2O2 formed per number of carbon atoms removed is similar to the degradation of FA and Ph with a factor of 1. Moreover, a comparative study on the formation of H2O2 was carried out in the presence of TiO2 rutile and TiO2 anatase, with commercial ZnO. Our results exhibit the impact of the presence of TiO2 on the decomposition of hydrogen peroxide and the formation of phenolic intermediates, which are much lower than those of ZnO only, which is in agreement with the formation of hydroxyl radicals °OH and superoxide O2°− degrading significantly hydroquinone (HQ), benzoquinone (BQ), and cathecol (CAT).

International audience; Solution-processed inorganic nanoporous films are key components for the vast spectrum of applications ranging from dew harvesting to solar cells. Shaping them into complex architectures required for advanced functionality, often need time-consuming or expensive fabrication. In this work, we show how crack formation is harnessed to pattern porous inorganic films in a single step and without using lithography. We developed aqueous ink formulations that, in the presence of polymeric latexes, enable evaporation-induced, defect-free periodic arrays of cracks with tunable dimensions over several centimeters. The ink formulation strategy was generalized to more than ten inorganic materials including simple and binary porous oxide and metallic films covering a whole spectrum of properties including insulator, photocatalytic, electrocatalytic, conductive or electrochromic materials. Notably, this approach enables three-dimensional self-assembly of cracks by stacking several layers of different compositions, yielding periodic assemblies of polygonal shapes and Janus-type patterns. The crack patterned periodic arrays of nanoporous TiO2 diffract light, and are used as temperature-responsive diffraction grating sensors. More broadly, this method represents a unique example of self-assembly process leading to long-range order (over several cm) in a robust and controlled way.

We elucidate the crucial role of the cetyl trimethylammonium bromide (CTAB) surfactant in the anisotropic growth mechanism of gold nano-bipyramids, nano-objects with remarkable optical properties and high tunability. Atomistic molecular dynamics simulations predict different surface coverages of the CTAB (positively charged) heads and their (bromide) counterions as function of the gold exposed surfaces. High concentration of CTAB surfactant promotes formation of gold nanograins in solution that work as precursors for the smooth anisotropic growth of more elongated nano-bipyramidal objects. Nanobipyramids feature higher index facets with respect to nanorods, allowing higher CTAB coverages that stabilize their formation and leading to narrower inter-micelles channels that smooth down their anisotropic growth. Absorption spectroscopy and scanning electron microscopy confirmed the formation of nanograins and demonstrated the importance of surfactant concentration on driving the growth towards nano-bipyramids rather than nanorods. The outcome explains the formation of the monodisperse bipyramidal nano-objects, the origin of their controlled shapes and sizes along with their remarkable stability.

Computational modeling and accurate simulations of localized surface plasmon resonance (LSPR) absorption properties are reported for gold nanobipyramids (GNBs), a class of metal nanoparticle that features highly tunable, geometrydependent optical properties. GNB bicone models with spherical tips performed best in reproducing experimental LSPR spectra while the comparison with other geometrical models provided a fundamental understanding of base shapes and tip effects on the optical properties of GNBs. Our results demonstrated the importance of averaging all geometrical parameters determined from transmission electron microscopy images to build representative models of GNBs. By assessing the performances of LSPR absorption spectra simulations based on a quasi-static approximation, we provided an applicability range of this approach as a function of the nanoparticle size, paving the way to the theoretical study of the coupling between molecular electron densities and metal nanoparticles in GNB-based nanohybrid systems, with potential applications in the design of nanomaterials for bioimaging, optics and photocatalysis., This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes

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International audience; Improving phosphor photoluminescence efficiency is a key parameter to boost the performances of many optical devices. In this work, colloidal silver nanocubes, homogeneously spread on a luminescent surface, have proved to help both injecting and extracting light in and out of the photoluminescent layer and hence contributed significantly to the enhancement of the fluorescence. This approach has been applied to two materials: the well-known Y3Al5O12:Ce yellow phosphor and an optical quartz. The emission efficiency, for sol–gel derived YAG:Ce layers, has increased 80% in the presence of an optimal nanoparticle density, whereas for quartz, a weakly fluorescent material, the photoluminescence signal can be enhanced by a 200-fold factor. A physical analysis based on simulations shows that the disorder is an important factor and that the surface density of Ag nanoparticles is a crucial parameter.

International audience; Increasing use of lasers in many different fields, from ultraviolet to near-infrared (NIR) wavelengths, requires the development of efficient broadband optical protections to ensure safety during their utilizations. Among the available technologies, nonlinear optical limiting appears as the most versatile and efficient one. Earlier research has focused on optical limiting materials for visible wavelengths. NIR wavelengths used in telecommunication or optical sensors such as for autonomous vehicles represent a highly challenging area with very few reports in particular in the solid state. This work discusses the preparation of efficient NIR optical filters combining azabodipy dyes with plasmonic nanoparticles in sol−gel monoliths. This strategy allows us to strongly enhance the nonlinear performance of the dyes, creating a synergy effect never observed on such a system in the NIR region.

International audience; The plasmonic features of gold nanomaterials provide intriguing optical effects which can find potential applications in various fields. These effects depend strongly on the size and shape of the metal nanostructures. For instance, Au bipyramids (AuBPs) exhibit intense and well-defined plasmon resonance, easily tunable by controlling their aspect ratio, which can act synergistically with chromophores for enhancing their photophysical properties. In Rose Bengal-nanoparticle systems it is now well established that the control of the dye-to-nanoparticle distance ranging from 10 to 20 nm as well as spectral overlaps is crucial to achieve appropriate coupling between the plasmon resonance and the dye, thus affecting its ability to generate singlet oxygen (1 O 2). We have developed AuBPs@mSiO 2 core-shell nanostructures that provide control over the distance between the metal surface and the photosensitizers for improving the production of 1 O 2 (metal-enhanced 1 O 2 production-ME 1 O 2). A drastic enhancement of 1 O 2 generation is evidenced for the resulting AuBPs and AuBPs@mSiO 2 in the presence of Rose Bengal, using a combination of three indirect methods of 1 O 2 detection, namely in operando Electron Paramagnetic Resonance (EPR) with 2,2,6,6-tetramethylpiperidine (TEMP) as a chemical trap, photooxygenation of the fluorescence probe anthracene-9,10-dipropionic acid (ADPA), and photooxygenation of methionine to methionine sulfoxide in a segmented flow microreactor.

International audience; The design of high-performance energy-converting materials is an essential step for the development of sensors, but the production of the bulk materials currently used remains costly and difficult. Therefore, a different approach based on the self-assembly of nanoparticles has been explored. We report on the preparation by solvothermal synthesis of highly crystalline CeF 3 nanodiscs. Their surface modification by bisphosphonate ligands led to stable, highly concentrated, colloidal suspensions in water. Despite the low aspect ratio of the nanodiscs (∼6), a liquidcrystalline nematic phase spontaneously appeared in these colloidal suspensions. Thanks to the paramagnetic character of the nanodiscs, the nematic phase was easily aligned by a weak (0.5 T) magnetic field, which provides a simple and convenient way of orienting all of the nanodiscs in suspension in the same direction. Moreover, the more dilute, isotropic, suspensions displayed strong (electric and magnetic) fieldinduced orientation of the nanodiscs (Kerr and Cotton−Mouton effects), with fast enough response times to make them suitable for use in electro-optic devices. Furthermore, an emission study showed a direct relation between the luminescence intensity and magnetic-field-induced orientation of the colloids. Finally, with their fast radiative recombination decay rates, the nanodiscs show luminescence properties that compare quite favorably with those of bulk CeF 3. Therefore, these CeF 3 nanodiscs are very promising building blocks for the development and processing of photosensitive materials for sensor applications.

International audience; The use of photosensitizers immobilized on mesoporous materials to produce singlet oxygen (1O2) has opened a new way to synthetic and environmental applications due to the fast development of flow photochemistry and continuous-flow microreactors. 1O2-based photosensitized processes can be employed for the degradation of organic pollutants in an aqueous medium and the photosensitizer can be covalently attached to the support and separated from the effluent reducing the environmental impact. The aim of the present paper is to evaluate the 1O2 generation of Rose Bengal (RB) in homogeneous and heterogeneous systems using in-operando evaluation. Mesoporous SiO2 nanoparticles (MSNs) were successfully conjugated with RB (MSN-RB) and electron paramagnetic resonance (EPR) spectroscopy in combination with the spin trap TEMP was employed to obtain paramagnetic TEMPO via generated 1O2 when RB or MSN-RB are exposed to visible light. Additionally, EPR/DMPO was used to exclude the possible generation of other reactive oxygen species (ROS) by the functionalized nanoparticles. We found that in situ 1O2 generation was enhanced when the same amount of RB is immobilized inside of mesoporous SiO2.

Two-photon lithography is a potential route to produce high-resolution 3D ceramics. However, the large shrinkage due to the elimination of an important organic counterpart of the printed material during debinding/sintering remains a lock to further development of this technology. To limit this phenomenon, an original approach based on a composite resin incorporating 45 wt% ultrasmall (5 nm) zirconia stabilized nanoparticles into the zirconium acrylate precursor is proposed to process 3D zirconia microlattices and nanostructured optical surfaces. Interestingly, the nanoparticles are used both as seeds allowing control of the crystallographic phase formed during the calcination process and as structural stabilizing agent preventing important shrinkage of the printed ceramic. After 3D photolithography and pyrolysis, the weight and volume loss of the microstructures are drastically reduced as compared to similar systems processed with the reference resin without nanoparticles, and stable 3D microstructures of cubic zirconia are obtained with high spatial resolution. In the case of a patterned surface, the refractive index of 2.1 leads to a diffraction efficiency large enough to obtain microfocusing with linewidths of 0.1 µm, and the demonstration of a microlens array with a period as small as 0.8 µm.

Neuroinflammation is a process common to several brain pathologies. Despites its medical relevance, it still remains poorly understood; there is therefore a need to develop new in vivo preclinical imaging strategies to monitor inflammatory processes longitudinally. We here present the development of a hybrid imaging nanoprobe named NP3, that was specifically designed to get internalized by phagocytic cells and imaged in vivo with MRI and bi-photon microscopy. NP3 is composed of a 16 nm core of gadolinium fluoride (GdF3), coated with bisphosphonate polyethylene glycol (PEG) and functionalized with a Lemke-type fluorophore. It has a hydrodynamic diameter of 28 ± 8 nm and a zeta potential of -42 ± 6 mV. The MR relaxivity ratio at 7 T is r1/r2 = 20; therefore, NP3 is well suited as a T2/T2* contrast agent. In vitro cytotoxicity assessments performed on four human cell lines revealed no toxic effects of NP3. In addition, NP3 is internalized by macrophages in vitro without inducing inflammation or cytotoxicity. In vivo, uptake of NP3 has been observed in the spleen and the liver. NP3 has a prolonged vascular remanence, which is an advantage for macrophage uptake in vivo. The proof-of-concept that NP3 may be used as a contrast agent targeting phagocytic cells is provided in an animal model of ischemic stroke in transgenic CX3CR1-GFP/+ mice using three complementary imaging modalities: MRI, intravital two-photon microscopy and phase contrast imaging with synchrotron X-rays. In summary, NP3 is a promising preclinical tool for the multiscale and multimodal investigation of neuroinflammation.

International audience; Neuroinflammation is a process common to several brain pathologies. Despites its medical relevance, it still remains poorly understood; there is therefore a need to develop new in vivo imaging strategies to monitor inflammatory processes longitudinally. We here present the development of a hybrid imaging nanoprobe named NP3, that was specifically designed to get internalized by phagocytic cells and imaged in vivo with MRI and bi-photon microscopy. NP3 is composed of a 16 nm core of gadolinium fluoride (GdF3), coated with bisphosphonate polyethylene glycol (PEG) and functionalized with a Lemke-type fluorophore (LEM-A). It has a hydrodynamic diameter of 28±8 nm and a zeta potential of-42±6 mV. The MR relaxivity ratio at 7T is r1/r2 = 20; therefore, NP3 is well suited as a T2/T2* contrast agent. In vitro cytotoxicity assessments performed on four human cell lines revealed no toxic effects of NP3. In addition, NP3 is internalized by macrophages in vitro without inducing inflammation or cytotoxicity. In vivo, uptake of NP3 has been observed in the spleen and the liver. NP3 has a prolonged vascular remanence, which is an advantage for macrophage uptake in vivo. The proof-of-concept that NP3 may be used as a contrast agent targeting phagocytic cells is provided in an animal model of ischemic stroke in transgenic CX3CR1-GFP/+ mice using three complementary imaging modalities: MRI, intravital two-photon microscopy and phase contrast imaging with synchrotron X-rays. In summary, 2 NP3 is a promising preclinical tool for the multiscale and multimodal investigation of neuroinflammation.

International audience; Two-photon lithography is a potential route to produce high-resolution 3D ceramics. However, the large shrinkage due to the elimination of an impor-tant organic counterpart of the printed material during debinding/sintering remains a lock to further development of this technology. To limit this phenomenon, an original approach based on a composite resin incorporating 45 wt% ultrasmall (5 nm) zirconia stabilized nanoparticles into the zirconium acrylate precursor is proposed to process 3D zirconia microlattices and nano-structured optical surfaces. Interestingly, the nanoparticles are used both as seeds allowing control of the crystallographic phase formed during the calcination process and as structural stabilizing agent preventing important shrinkage of the printed ceramic. After 3D photolithography and pyrolysis, the weight and volume loss of the microstructures are drastically reduced as compared to similar systems processed with the reference resin without nanoparticles, and stable 3D microstructures of cubic zirconia are obtained with high spatial resolution. In the case of a patterned surface, the refractive index of 2.1 leads to a diffraction efficiency large enough to obtain microfo-cusing with linewidths of 0.1 μm, and the demonstration of a microlens array with a period as small as 0.8 μm

In the past few years, the efforts of scientists in the field of nanoparticle design have focused on building 2D and 3D macroscopic objects from controlled assembly processes. Among the few proposed methods, the preparation of aerogels allows production of 3D monolithic materials of several centimeters in size with desired porosity. The use of nanocrystals as building blocks provides access to highly crystalline macroscopic structures, imitating porous crystals. Herein, a general and versatile approach to aerogels development starting from aqueous colloidal solutions is introduced. A strong and abrupt change of the dielectric constant of the nanoparticle dispersion solvent induces formation of homogeneous and stable gels. The drying of these gels, under supercritical conditions, leads to transparent aerogels. By this approach, Y3Al5O12:Ce and GdF3 monolithic aerogels are prepared for the first time, opening the route to a broad range of chemical compositions with metal oxides and fluorides. Additionally, ...

International audience; Monolithic silica sol-gel glasses doped with platinum(II) acetylide complexes possessing respectively four or six phenylacetylene units (PE2-CH2OH and PE3-CH2OH) in combination with various concentrations of spherical and bipyramidal gold nanoparticles (AuNPs) known to enhance non-linear optical absorption, were prepared and polished to high optical quality. The non-linear absorption of the glasses was measured and compared to glasses doped solely with AuNPs, a platinum(II) acetylide with shorter delocalized structure, or combinations of both. At 532 nm excitation wavelength the chromophore inhibited the non-linear scattering previously found for glasses only doped with AuNPs. The measured non-linear absorption was attributed to reverse saturable absorption from the chromophore, as previously reported for PE2-CH2OH/AuNP glasses. At 600 nm strong nonlinear absorption was observed for the PE3-CH2OH/AuNPs glasses, also attributed to reverse saturable absorption. But contrary to previous findings for PE2-CH2OH/AuNPs, no distinct enhancement of the non-linear absorption for PE3-CH2OH/AuNPs was observed. A numerical population model for PE3-CH2OH was used to give a qualitative explanation of this difference. A stronger linear absorption in PE3-CH2OH would cause the highly absorbing triplet state to populate quicker during the leading edge of the laser pulse and this would in turn reduce the influence from two-photon absorption enhancement from AuNPs.

International audience; An optical power limiter (OPL) device can change its optical properties depending on the input light intensity: it is ideally transparent at low incident power and presents a decrease in transmission when the incident intensity increases. This phenomenon can be used for protection of optical sensors. This paper presents the design of a functionalized aza-BODIPY chromophore, combining good nonlinear two-photon absorption and exited-state absorption in the short-wave infrared range (1300-1600 nm). The aza-BODIPY chromophores also show excellent thermal and photochemical stabilities. Their covalent grafting to a sol-gel matrix leads to the formation of class II sol-gel materials that allows for extraordinary doping concentrations of up to 280 mol·L-1 (40 wt %), which results in highly efficient OPL performances at 1550 nm. © 2020 American Chemical Society.

International audience; High resolution fabrication using two-photon lithography is extensively studied for a large range of materials, from polymer to inorganics. Hybrid materials including a sol-gel step have been developed since two decades to increase mechanical or optical properties in particular on silicon based materials. Among the metal oxide, few studies have been dedicated to titanium and, because of the high reactivity of titanium precursors, obtaining a resin with a high part of titanium is challenging. Indeed, resins for two-photon lithography have to be stable for the processing time and titanium precursors are more difficult to operate due to their higher reactivity and often require drastic working conditions in order to control the chemical processes. Here, we propose a method, working at ambient conditions, to print submicronic structures of organic-inorganic hybrids with a large proportion of titanium and ceramics using high resolution two-photon process. The material obtained and its evolution during the pyrolysis at 600°C and 1000°C are characterized. We show that TiO2/SiO2 based micro-ceramics can be obtained after the pyrolysis of the microstructures. The respective roles of the two chemical reactions involved in this lithography process, sol-gel condensation and radical photopolymerization, are highlighted.

A common molecular design paradigm for optical power limiting (OPL) applications is to introduce heavy atoms that promote intersystem crossing and triplet excited states. In order to investigate this effect, three multi-branched fluorene molecules were prepared where the central moiety was either an organic benzene unit, para-dibromobenzene, or a platinum(II)&ndash, alkynyl unit. All three molecules showed good nanosecond OPL performance in solution. However, only the dibromobenzene and Pt&ndash, alkynyl compounds showed strong microsecond triplet excited state absorption (ESA). To investigate the photophysical cause of the OPL, especially for the fully organic molecule, photokinetic measurements including ultrafast pump&ndash, probe spectroscopy were performed. At nanosecond timescales, the ESA of the organic molecule was larger than the two with intersystem crossing (ISC) promoters, explaining its good OPL performance. This points to a design strategy where the singlet-state ESA is balanced with the ISC rate to increase OPL performance at the beginning of a nanosecond pulse.

Gold nanoparticles offer unique optoelectronic properties relevant for a wide range of processes and products, in biology and medicine (therapeutic agents, diagnostic, drug delivery), as well as in electronics, photovoltaics, and catalysis. So far, various synthesis methods proposed have led to rather limited concentration and purity of the colloidal suspensions, severely hindering their use. Here, we present a simple and versatile procedure for the synthesis of gold pentatwinned nanostructures, including nanobipyramids based on a seed-mediated growth process that overcomes the concentration limitations of current methods by 2 orders of magnitude. Moreover, our novel process offers quantitative yields while easily allowing a fine control of the particles' shape, size (with a high monodispersity), and plasmonic properties. Finally, we demonstrate that our method can be easily upscaled to produce large amounts of nanostructures, up to the gram scale, with minimal waste and postprocessing, thus facilitating their use for further applications and industrial developments.

International audience; The aim of the work was to study photocatalytic activity of composite TiO2/Au/SiO2 thin films. Coatings were prepared using sol-gel technique. Physicochemical parameters of coatings were characterized using UV–vis spectrometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES), ellipsometry, tactile measurements, goniometry and diffuse reflectance measurements. The photocatalytic activity of the films was tested in batch mode using aqueous solution of formic acid. Changes of formic acid concentration were determined by means of high pressure liquid chromatography (HPLC). Increase of initial degradation rate of formic acid was detected for TiO2/Au/SiO2 films with gold nanoparticle’s load 0.5 wt.% and 1.25 wt.%. However, deeper insights using more detailed characterization of these coatings demonstrated that the improvement of the photocatalytic activity is more probably attributed to an increase in the areal loading of TiO2.

International audience; The aim of the this work was to study feasibility of titanium dioxide thin films prepared by atomic layer deposition (ALD) technique on aluminum foam substrates for photocatalysis and compare performance of thin films with commercially available AEROXIDE® TiO2. Formic acid and phenol photocatalytic decomposition was monitored using high-pressure liquid chromatography (HPLC). The morphology and thickness of TiO2 films were characterized by scanning electron microscopy (SEM) and their structure was determined by X-ray diffraction (XRD). Surface of the thin films was characterized with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The amount of TiO2 deposited on aluminum foam was measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). It was observed that initial rates of formic acid and phenol degradation were 0.007 and 0.001 mmol L−1 min−1, respectively. The apparent quantum yields for formic acid using immobilized and reference TiO2 powder (AEROXIDE® TiO2 P25, Evonik) were 2.2 and 2.7%, correspondingly. While for phenol apparent quantum yield was equal to 0.4% when TiO2 thin film was used and 0.7% in the case of reference powder. A decrease of the photocatalytic activity of TiO2 films deposited on aluminum foam was observed after the first cycle for both model compounds. It was suggested from this study that suppression of activity occurs due to detachment of TiO2 from the surface of thin film.

International audience; The efficient materials for Li-ion battery electrodes require suitable composition, high-crystallinity and appropriate structuration. The last one is important to assure an efficient exchange of Li ions between the anode and electrolyte, thus enhancing the kinetics of electrochemical reactions. Therefore, the synthesis of well-crystallized nano-sized electrode materials exhibiting high surface area is of great interest. Herein, we explore the influence of the glycothermal synthesis variations on the structure and porosity of Li4Ti5O12. The utilized precursors and their concentration have a minor influence on crystallites size, but they could be used to control the porosity of assembled particles. The prepared Li-ion battery anode could be charged at low and high rate reaching the theoretical capacity of Li4Ti5O12. The material retains its peculiar porous structuration even after 1000 cycles at charging/discharging rate of 50C which contributes to the lack of capacity fading. Additionally, 7Li NMR is performed on one of synthesized nano-structured Li4Ti5O12 and compared with commercially available nanosized Li4Ti5O12 to understand the excellent electrochemical performance. Open image in new window Glycothermal synthesis of lithium titanate, in 1,4-butanediol leads to crystalline NPs of 4-5 nm assembled into highly porous microstructures. Such structuration assures well-developed contact area between the electrode and an electrolyte in Li-ion batteries, which facilitates exchange of Li-ions. Therefore, the material shows excellent electrochemical performances. LTO characterized by different nanostructuration is obtained by varying the synthesis conditions (precursors type and concentration, temperature and co-solvent). , Highlights Pure nanostructure Li4Ti5O12 was synthesized in varying glycothermal conditions using 1,4-butanediol as the solvent. Simple adjustment of precursors and their concentration tuned the microstructure of the material without affecting the size of crystallites which oscillated around 4 nm. Nano-scaling and proper microstructuration is an effective way to improve kinetics of electrochemical reactions due to the efficient exchange of Li ions between electrodes and electrolytes. 7Li NMR was performed on synthesized material and commercial one in order to understand the peculiar electrochemical properties of the material.

Composite TiO2/SiO2 porous coatings modified with bipyramid-like gold nanoparticles were prepared by means of sol-gel and inkjet printing technique, comprehensively characterized and studied for photocatalytic disinfection of drinking water with fecal contamination by natural bacteria consortia. Photocatalytic antimicrobial activity of prepared thin films was evaluated against gram-negative (Escherichia coli and Total coliforms) and gram-positive bacteria (Enterococci). Elimination rate of all tested bacteria increased when photocatalytic coatings were used in comparison with solar disinfection. The best results in terms of antimicrobial activity were obtained with TiO2/SiO2/Au thin films under natural solar radiation, which demonstrated the highest antimicrobial activity, enhancing the inactivation rates of E. coli, Total coliforms and Enterococci 1.5, 1.3 and 1.6 times, respectively as compared to solar disinfection without photocatalyst. Remarkable difference in bacteria sensitivity for photocatalytic disinfection was observed with trend E. coli > Total coliforms > Enterococci. No release of gold and titanium was detected during photocatalytic water disinfection test. Regrowth of E. coli, Total coliforms and Enterococci after photocatalytic bacteria inactivation under UVA-LED and natural solar radiation was lower than 1% (24, 48 and 72 h), indicating potential application of prepared coatings for production of safe drinking water.

International audience; We present fluorescence and a random lasing enhancement effect due to the interaction between gold nanoparticles (AuNPs) and Rhodamine 6G (Rh6G) dye. Non-covalently bounded dyes in the proximity of nanoparticles are studied in three systems of varying dimensionality: from (i) three-dimensional freely distributed suspensions, through (ii) quasi-two-dimensional multilamellar liposomes, to (iii) solid two-dimensional thin layers. Liposomes facilitate the formation of stable AuNPs/Rh6G composition showing enhanced fluorescence, while solid thin films exhibit plasmon-assisted random lasing.

International audience; The intrinsic properties of silica aerogels make them well suited for applications requiring high surface area. Therefore, the dispersion of functional nanoparticles (NPs) in these highly porous structures gives access to materials for wide range of applications such as catalysis, energy storage or sensing. The last one is particularly interesting if such composites possess good optical quality. Herein, the synthesis of monolithic and transparent silica aerogels highly loaded with Y3Al5O12:Ce nanocrystals (NCs) (up to 50 wt %) is reported. The developed composite aerogels can be impregnated with liquids, contrary to most of existing aerogels, which crack because of the strong capillary forces. Therefore, this system is designed as a novel concept of 3D porous scintillator, using the efficient photoluminescent and scintillating properties of Y3Al5O12:Ce. The investigated fluid containing low-energetic ionizing radiation emitters impregnates the material, which assures the efficient harvesting of radiation because of highly developed surface area. Such composites prove to be efficient new-type detectors of low-energy beta radiation both in liquids and gases.

International audience; Real time in vivo detection of Amyloid β (Aβ) deposits at an early stage may lead to faster and more conclusive diagnosis of Alzheimer’s disease (AD) and can facilitate the follow up of the effect of therapeutic interventions. In this work, the capability of new hybrid nanomaterials to target and detect Aβ aggregates using magnetic resonance (MRI) and fluorescence imaging is demonstrated. These smart contrast agents contain paramagnetic nanoparticles surrounded by luminescent conjugated oligothiophenes (LCOs) known to selectively bind to Aβ aggregates, with emission spectra strongly dependent on their conformations, opening the possibilities for several fluorescence imaging modes for AD diagnostics. Relaxivity is evaluated in vitro and ex vivo. The capability of these contrast media to link to Aβ fibrils in stained sections is revealed using transmission electron microscopy and fluorescence microscopy. Preliminary in vivo experiments show the ability of the contrast agent to diffuse through the blood–brain barrier of model animals and specifically stain amyloid deposits.

International audience; In this work, we demonstrate the feasibility of gold bipyramidal-shaped nanoparticles (AuBPs) to be used as active plasmonic nanoplatforms for the detection of the biotin–streptavidin interaction in aqueous solution via both Localized Surface Plasmon Resonance and Surface Enhanced Raman Scattering (LSPR/SERS). Our proof of concept exploits the precise attachment of the recognition element at the tips of AuBPs, where the electromagnetic field is stronger, which is beneficial to the surface sensitivity of longitudinal LSPR on the local refractive index and to the electromagnetic enhancement of SERS activity, too. Indeed, successive red shifts of the longitudinal LSPR associated with increased local refractive index reveal the attachment of para-aminothiophenol (p-ATP) chemically labeled Biotin to the Au surface and the specific capture of the target protein by biotin-functionalized AuBPs. Finite-Difference Time-Domain simulations based on the reconstructed index of refraction confirm LSPR measurements. However, the molecular identification of the biotin–streptavidin interaction remains elusive by LSPR investigation alone. Remarkably, we succeeded to complement the LSPR detection with reliable SERS measurements which permitted to (a) certify the molecular identification of biotin–streptavidin interaction and (b) extend the limit of detection of streptavidin in solution toward 10–12 M. Finally, to further probe the possibility to implement the AuBPs as dual LSPR-SERS based immunoassays in solution for real clinical diagnostics, we additionally investigated the AuBP’s performance to transduce the specific antihuman IgG- human IgG binding event, providing thus a reference design for building unique plasmonic immunoassays for dual-optical detection of target proteins in aqueous solution.

International audience; Fluorescent gold nanoparticles (GNPs) were prepared by chain-end grafting of RAFT copolymers bearing multiple fluorophores distributed along the chain. Two different synthetic approaches in water were first studied with well-defined and biocompatible homopolymers. Both led to very stable samples and the corona thickness at the gold surface increased with the polymer molecular weight. The two-step ligand exchange approach was then selected to synthesize GNPs grafted with polymer–chromophore conjugates exhibiting different molecular weights, backbone architectures and chromophores. Again, the thickness of the organic corona increased with the polymer molecular weight but was also dependent on the conformation of the conjugate chains which depends on the nature of the chromophores. By adjusting these parameters, it was possible to control the average chromophore–gold distance which is of paramount importance for the fluorescence properties of the nanoparticles. We indeed showed that the fluorescence of the hybrid nano-objects increased with the corona thickness.

Sensitive, robust and stable sensors are required to bring biosensing techniques from the forefront of research to clinical and commercial settings. To this end, we report on the development of new robust plasmonic sensors consisting of gold nano-bipyramids (BPs) grafted to a glass substrate via silanization, associated with a novel setup based on Spatial Modulation Spectroscopy allowing the measurement of the optical response of individual nano-objects in a liquid environment. We thereby show that changes in the refractive index of the medium around individual silanized BPs can be detected by measuring their plasmonic shift with sensitivities comparable to values reported elsewhere and in good agreement with theoretical calculations. The optical response is furthermore shown to be stable and robust allowing for repeated measurements in different media and storage over many months. This work opens up new perspectives in the field of plasmonic bio-sensing as our setup is readily adaptable to dynamic liquid measurements and a wide range of applications such as the detection of clinically important analytes or pollutants in water.

High-performance Li-ion batteries require materials with well-designed and controlled structures on nanometre and micrometre scales. Electrochemical properties can be enhanced by reducing crystallite size and by manipulating structure and morphology. Here we show a method for preparing hierarchically structured Li4Ti5O12 yielding nano- and microstructure well-suited for use in lithium-ion batteries. Scalable glycothermal synthesis yields well-crystallized primary 4–8 nm nanoparticles, assembled into porous secondary particles. X-ray photoelectron spectroscopy reveals presence of Ti+4 only; combined with chemical analysis showing lithium deficiency, this suggests oxygen non-stoichiometry. Electron microscopy confirms hierarchical morphology of the obtained material. Extended cycling tests in half cells demonstrates capacity of 170 mAh g−1 and no sign of capacity fading after 1,000 cycles at 50C rate (charging completed in 72 s). The particular combination of nanostructure, microstructure and non-stoichiometry for the prepared lithium titanate is believed to underlie the observed electrochemical performance of material., Both electronic and ionic transport must be optimized in Li4Ti5O12 for its use in Li-ion batteries, most promisingly against high voltage cathodes. Here authors synthesize hierarchical porous micrometre-scale structures composed of primary nanoparticles to demonstrate an attractive combination of rate performance, capacity and cycling stability.

International audience; We describe the design of original nanocarriers that allows for ultrahigh chromophore loading while maintaining the photo-activity of each individual molecule. They consist in shells of charged biocompatible polymers grafted on gold nanospheres. The self-organization of extended polymer chains results from repulsive charges and steric interactions that are optimized by tuning the surface curvature of nanoparticles. This type of nano-scaffolds can be used as light-activated theranostic agents for fluorescence imaging and photodynamic therapy. We demonstrate that, labeled with a fluorescent photosensitizer, it can localize therapeutic molecules before triggering the cell death of B16-F10 melanoma with an efficiency that is similar to the efficiency of the polymer conjugate alone, and with the advantage of extremely high local loading of photosensitizers (object concentration in the picomolar range).

International audience; Light-matter interactions are of great interest for potential biological applications (bioimaging, biosensing, phototherapy). For such applications, sharp nanostructures exhibit interesting features since their extinction bands (surface plasmon resonance) cover a large bandwidth in the whole visible wavelength region due to the existence of ?hot spots? located at the end of the tips. In this context, gold nanostars appear to be interesting objects. However, their study remains difficult, mainly due to complicated synthetic methods and further functionalization. This paper reports the synthesis, functionalization, and photophysics of luminescent hybrid gold nanostars prepared using a layer-by-layer (LbL) deposition method for the tuning of chromophore-to-particle distances together with the impact of the spectral overlap between the plasmon and the emission/absorption of the dyes. Several luminescent dyes with different optical signatures were selectively adsorbed at the nanoparticle surface. The optimized systems, exhibiting the highest luminescence recovery, clearly showed that overlap must be as low as possible. Also, the fluorescence intensities were quenched in close vicinity of the metal surface and revealed a distance-dependence with almost full recovery of the dyes emission for 11 LbL layers, which corresponded to 15 nm distances evaluated on dried samples. The photophysics of the luminescent core?shell particles were carried out in suspension and correlated with the response of isolated single objects.

International audience; Two-photon excitation of photobases is used to induce pH changes and control the condensation step of the sol–gel process at the focal point of a laser beam in a confocal configuration. This two-photon microfabrication process, which is usually used in the polymerization of organic monomers, enables the generation of 2D and 3D inorganic Si–O–Si networks of silica based materials with micron resolution. Different variables for the formulation are studied, including the mechanism of condensation, the type of photo initiator, the solvent and the concentration used, as well as the laser parameters.

International audience; The synthesis of well-defined oxide nanocrystals (NCs) with high crystallinity and ultra-small size (typically below 5 nm) is extremely challenging in view of their numerous important related applications. Often the obtained products suffer from particle aggregation, hindering beneficial advantages of nano-size character such as low light scattering properties. Solvothermal methods are very powerful synthetic approaches toward such nanocrystals especially when polyols are used as solvents. Their unique properties and gradual changes in a homologous series of polyols provide a wide range of tools for reaction design. A prominent example of such a reaction is the glycothermal synthesis of Y3Al5O12 (YAG) in 1,4-butanediol in which 20 nm aggregated nanoparticles can be obtained. Herein, we introduce a key evolution of YAG:Ce nanoparticles prepared via a modified glycothermal approach. We emphasize the crucial role of the co-solvent together with the amount of water. Addition of DEG and dehydration of precursors lead to 4 nm non-aggregated nanocrystals with high crystallinity and the correspondingly high photoluminescence emission. Very clear and stable colloidal solutions with concentrations of nanocrystals up to 50% are obtained. The prepared colloids are directly used for the fabrication of homogenous, luminescent and crack-free thin films without the addition of any plasticisers or surfactants. The thickness of the films is simply and efficiently controlled by the concentration of the colloidal solution.

The development of new photonic materials is a key step toward improvement of existing optical devices and for the preparation of a new generation of systems. Therefore synthesis of photonic hybrid materials with a thorough understanding and control of the microstructure-to-properties relationships is crucial. In this perspective, a new preparation method based on fast gelation reactions using simple dispersion of dyes without strong covalent bonding between dye and matrix has been developed. This new sol-gel method is demonstrated through synthesis of monolithic siloxane-based hybrid materials highly doped by various platinum(II) acetylide derivatives. Concentrations of the chromophores as high as 400 mM were obtained and resulted in unprecedented optical power limiting (OPL) performance at 532 nm of the surface-polished solids. Static and time-resolved photoluminescence of the prepared hybrid materials were consistent with both OPL data and previous studies of similar Pt(II) compounds in solution. The impacts of the microstructure and the chemical composition of the matrix on the spectroscopic properties, are discussed.

International audience; The complexing properties of a thiacalix[2]thianthrene 1 and its disulfoxide derivative 2 toward alkali metal, alkaline earth metal, some transition metal and some heavy metal cations have been investigated in acetonitrile by means of UV spectrophotometry. At the concentrations suited to this technique, complexation of the alkali metal cations by the sulfoxide but not the thiacalixthianthrene was detectable, whereas the converse was true for both transition metal and lanthanide cations. Complexation of the alkaline earth cations was not detectable. The strongest binding observed was that of Hg(II) to ligand 1 but in no case was complexation sufficiently strong for either ligand to function as a useful metal ion extractant. Graphical Abstract The complexing properties of a thiacalix[2]thianthrene 1 and its disulfoxide derivative 2 toward alkali metal, alkaline earth metal, some transition metal and some heavy metal cations have been investigated in acetonitrile by means of UV spectrophotometry. At the concentrations suited to this technique, complexation of the alkali metal cations by the sulfoxide but not the thiacalixthianthrene was detectable, whereas the converse was true for both transition metal and lanthanide cations. Complexation of the alkaline earth cations was not detectable. The strongest binding observed was that of Hg(II) to ligand 1 but in no case was complexation sufficiently strong for either ligand to function as a useful metal ion extractant.

The growth of silver nanoparticles in mesostructured hybrid silica films under laser illumination is investigated by optical absorption spectroscopy and transmission electron microscopy. At low laser doses in the UV range, a blue-shift of the plasmon resonance is observed for increasing particle size. This size dependence is interpreted on the basis of the Mie theory assuming a two-layer core−shell model resulting from the localization of the nanoparticles in the block copolymer part of the film. At higher laser doses, the observed red-shift of the resonance wavelength and decrease of the absorbance level at resonance are attributed to the formation of a high refractive index shell around the nanoparticles that thickens slowly with the dose. The growth kinetics of silver nanoparticles is also studied for different illumination wavelengths in the UV and visible ranges. Surprisingly, the nanoparticles also grow under visible illumination. This is partly attributed to the release of electrons by the degradin...