From gold nanoparticles to luminescent nano-objects: experimental aspects for better gold-chromophore interactions

International audienceGold nanoparticles have been the center of interest for scientists since many decades. Within the last 20 years, the research in that field has soared with the possibility to design and study nanoparticles with controlled shapes. From spheres to more complex shapes such as stars, or anisotropic architectures like rods or bipyramids, these new systems feature plasmonic properties making them the tools of choice for studies on light-matter interactions. In that context, fluorescence quenching and enhancement by gold nanostructures is a growing field of research. In this review, we report a non-exhaustive summary of the synthetic modes for various shapes and sizes of isotropic and anisotropic nanoparticles. We then focus on fluorescent studies of these gold nano-objects, either considering “bare” particles (without modifications) or hybrid particles (surface interaction with a chromophore). In the latter case, the well-known metal-enhanced fluorescence (MEF) is more particularly developed; the mechanisms of MEF are discussed in terms of the additional radiative and non-radiative decay rates caused by several parameters such as the vicinity of the chromophore to the metal or the size and shape of the nanostructures

Controlled surface modification of gold nanostructures with functionalized silicon polymers

International audienceThe stabilization of metal nanoparticles using surface modification has been intensively investigated. We propose an alternative to the use of surfactants, long-chain polymers or silica shells in order to provide easy and efficient stabilization of a wide range of metallic nanostructures. The prepared silicon oligomers were characterized, optimized and successfully used for surface modifications of nanospheres, nanobipyramids, nanorods of both gold and silver. The modified nanoparticles were then easily incorporated into monolithic sol–gel materials based on silica. This original route toward hybrid composite was efficiently used to prepare composite sol–gel materials with plasmonic nanostructures for optical applications. Graphical Abstract Specifically designed silicon polymers are used to efficiently stabilize metal nanoparticles and allow homogeneous dispersion into sol–gel materials

Tuning Dye-to-Particle Interactions toward Luminescent Gold Nanostars

International audienceLight-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

Bioavailability of immobilized epidermal growth factor: Covalent versus noncovalent grafting

In an effort to rationalize and optimize an antiapoptotic coating combining chondroitin sulfate (CS) and epidermal growth factor (EGF) for vascular applications, the authors here report the comparison of two grafting strategies aiming to display EGF in an oriented fashion on CS. For that purpose, the authors produced, purified, and characterized a chimeric protein corresponding to EGF that was N-terminally fused to a cysteine and a coil peptide. The chimera was covalently immobilized via its free thiol group or captured via coiled\u2013coil interactions at the surface of a biosensor or on a chondroitin sulfate coating in multiwell plates, mimicking the coating that was previously developed by them for stent-graft surfaces. The interactions of grafted EGF with the soluble domain of its receptor or the impact of grafted EGF upon vascular smooth muscle survival in proapoptotic conditions indicated that the coiled\u2013coil based tethering was the best approach to display EGF. These results, combined to direct enzyme-linked immunosorbent assay measurements, indicated that the coiled\u2013coil tethering approach allowed increasing the amount of bioavailable EGF when compared to covalent coupling, rather than the total amount of grafted EGF, while using much lower concentrations of tagged EGF during incubation.Peer reviewed: YesNRC publication: Ye

Enhanced photocatalytic activity through insertion of plasmonic nanostructures into porous TiO2/SiO2 hybrid composite films

SSCI-VIDE+CARE+CGUInternational audienceComposite TiO2/SiO2 porous thin films prepared using the sol–gel process were doped with dispersion of bipyramid-like gold nanoparticles (AuBP). The impact of the presence of the nanoparticles on the photocatalytic activity during degradation of formic acid in aqueous media was fully investigated and an improvement of the efficiency was observed. The films compositions and structures were characterized by means of UV–vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), goniometry, and diffuse reflectance measurements. The photocatalytic activity was evaluated through decomposition of formic acid and correlated with the structure and the spectroscopic characterizations. The best results in terms of photocatalysis were obtained with thin films doped with 1 wt.% of AuBP; more specifically, the initial degradation rate of formic acid was nearly two times higher than with the undoped reference. It was observed that after three cycles the performance of the prepared photocatalyst does not undergo significant changes. No photocatalytic activity was detected for any of the synthesized thin films under visible light irradiation alone. The photocatalytic improvement was correlated with the lowering of the band gap of TiO2

Long Distance Enhancement of Nonlinear Optical Properties Using Low Concentration of Plasmonic Nanostructures in Dye Doped Monolithic Sol-Gel Materials

International audienceMonolithic sol–gel silica composites incorporating platinum-based chromophores and various types of gold nanoparticles (AuNPs) are prepared and polished to high optical quality. Their photophysical properties are investigated. The glass materials show well-defined localized surface plasmon resonance (SPR) absorbance from the visible to NIR. No redshifts of the AuNP plasmon absorption peaks due to the increase in nanoparticle doping concentration are observed in the glasses, proving that no or very small SPR coupling effects occur between the AuNPs. At 600 nm excitation, but not at 532 nm, the AuNPs improve the nonlinear absorption performance of glasses codoped with 50 × 10−3 m of a Pt-acetylide chromophore. The glasses doped with lower concentrations of AuNPs (2–5 μm average distance) and 50 × 10−3 m in chromophore, show a marked improvement in nonlinear absorption, with no or only small improvement for the more highly AuNP doped glasses. This study shows the importance of excitation wavelength and nanoparticle concentration for composite systems employing AuNPs to improve two-photon absorption of chromophores

Detection of beta-emitters in gas with YAG:Ce highly porous aerogels

International audienceBeta emitting radioisotopes are challenging to detect and differentiate due to their rather short mean free path in air at low kinetic energies (up to tens of keV). In concert with importance of these isotopes to nuclear security and their presence in the air it is of special interest to search a detection method of beta ray emitters such as 85Kr, 133Xe, 3H and even 37Ar. In metrology, for some of these isotopes, the current method consist in bubbling these gas in water which is then mix in a liquid scintillator. However, this method produces a waste product that is a mixture of organic and aqueous compounds and radioactivity.. In addition, these can hardly be operated in out of a lab and is a delayed measurement requiring source preparation. Our aim is to develop a full solid-state scintillating detector where the radioactive gas is penetrating the scintillator, as in the case of bubbles in a liquid. Our strategy is based on highly porous scintillating materials made of scintillating inorganic nanoparticles. In this frame we have developed dedicated highly concentrated colloidal solution of YAG:Ce nanoparticles. These starting solutions allow to prepare gels and then aerogels using supercritical drying. This novel material possesses a very high porosity (density about 0.2). The important properties for the detection of isotopes are the requirement for a rather fast decay time and a good scintillation yield. The nanoparticles and the aerogels were investigated under the X-ray excitations and 450 nm excitations. While hydrogen-calcinated powders (and aerogels), are showing higher photoluminescence efficiencies under optical excitation, air-calcinated are exhibiting faster decay times and better scintillation yields highlighting the extreme sensitivity of the nanoparticles the Ce3+/Ce4+ valence state. After optimization of the thermal annealing, the aerogels have been measured under live radioactive gas (85Kr) tests using the triple to double coincidence method, a standard method in metrology of radioactivity detection and the aerogels demonstrate already the highest high triple/double coincidence ratios and total counts ever achieved. Preliminary results on the monte-carlo simulation for various geometries will also be presented

Detection of beta-emitters in gas with YAG:Ce highly porous aerogels

International audienceBeta emitting radioisotopes are challenging to detect and differentiate due to their rather short mean free path in air at low kinetic energies (up to tens of keV). In concert with importance of these isotopes to nuclear security and their presence in the air it is of special interest to search a detection method of beta ray emitters such as 85Kr, 133Xe, 3H and even 37Ar. In metrology, for some of these isotopes, the current method consist in bubbling these gas in water which is then mix in a liquid scintillator. However, this method produces a waste product that is a mixture of organic and aqueous compounds and radioactivity.. In addition, these can hardly be operated in out of a lab and is a delayed measurement requiring source preparation. Our aim is to develop a full solid-state scintillating detector where the radioactive gas is penetrating the scintillator, as in the case of bubbles in a liquid. Our strategy is based on highly porous scintillating materials made of scintillating inorganic nanoparticles. In this frame we have developed dedicated highly concentrated colloidal solution of YAG:Ce nanoparticles. These starting solutions allow to prepare gels and then aerogels using supercritical drying. This novel material possesses a very high porosity (density about 0.2). The important properties for the detection of isotopes are the requirement for a rather fast decay time and a good scintillation yield. The nanoparticles and the aerogels were investigated under the X-ray excitations and 450 nm excitations. While hydrogen-calcinated powders (and aerogels), are showing higher photoluminescence efficiencies under optical excitation, air-calcinated are exhibiting faster decay times and better scintillation yields highlighting the extreme sensitivity of the nanoparticles the Ce3+/Ce4+ valence state. After optimization of the thermal annealing, the aerogels have been measured under live radioactive gas (85Kr) tests using the triple to double coincidence method, a standard method in metrology of radioactivity detection and the aerogels demonstrate already the highest high triple/double coincidence ratios and total counts ever achieved. Preliminary results on the monte-carlo simulation for various geometries will also be presented

Rare-earth doped micro-emitters made by lift-off processing in pulsed laser deposited layers on Si substrate

International audienceRare earth emitters are promising in integrated optics but require complex integration on silicon. In this work, we have fabricated an Y 2 O 3 :Eu 3+ micro-emitter on SiO 2 on Si substrate without etching. Since pulsed laser deposition produces a high quality layer at room temperature, material can be locally deposited on top of substrates by lift-off processing. After annealing, microstructures exhibit good crystallographic quality with controlled dimensions for light confinement and narrow emission. This works allows envisioning rare-earth doped micro-photonic structures directly integrated on silicon without etching, which opens the way to integration of new functional materials on silicon platform

Synthesis and optical properties of dyes encapsulated in gold hollow nanoshells

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