Approches colloïdale et bio-inspirée en nanoplasmonique

Le confinement et le guidage de l'énergie lumineuse à l'échelle nanométrique dans des composants colloïdaux requiert le contrôle précis (i) de la morphologie des nanoparticules, (ii) de leur agencement spatial dans des architectures d'ordre supérieur et (iii) du couplage entre structures plasmoniques et molécules photoactives. Ce travail de thèse explore des approches nouvelles de synthèse, essentiellement bio-inspirées, de ces trois défis. Dans un premier temps, nous avons utilisé les principes de biominéralisation pour ajuster le couplage entre plasmon et fluorophore et ainsi contrôler l'exaltation de fluorescence. La fluorescence d'ensembles finis et organisés de fluorophores (porphyrines) appelé agrégats J est modulée par leur encapsulation dans une fine couche de silice d'épaisseur contrôlée (entre 2 ± 1 nm et 12 ± 1 nm) produite par minéralisation, suivie de l'accrochage de nanoparticules d'or ou d'argent. Les agrégats J servent de template à la minéralisation silicée qui renforce alors leur stabilité mécanique, permet d'adsorption spécifique de nanoparticules métalliques et joue le rôle d'espaceur diélectrique permettant une optimisation du couplage exciton-plasmon. L'exaltation de fluorescence par les plasmons a ainsi pu être optimisée à plus de 400% et 200% par conjugaison de particules d'argent et d'or respectivement sur les agrégats J minéralisés. Notre approche colloïdale ascendante pourrait contribuer à la conception de sondes optiques pour des applications capteurs ou en imagerie mais s'inscrit aussi dans la recherche de systèmes efficaces pour le traitement de l'information optique par intégrations de structures plasmoniques cristallines et d'absorbeurs /émetteurs moléculaires. Dans un deuxième temps, nous avons exploré de nouvelles méthodes de contrôle de la morphologie de nanoparticules métalliques et de leur auto-assemblage en utilisant des protéines artificielles appelées α-Repins. Le principal avantage de ces protéines artificielles est leur grande stabilité thermique et leur structure tridimensionnelle robuste et modulable par concaténation de portions de séquence tout en permettant une variabilité de certains acides aminés. Pour la première fois, ces protéines ont été utilisées comme agents directeurs de croissance de nanoparticules d'or, ce qui nous a permis de produire des particules sphériques, prismatiques triangulaires, des nanobâtonnets par effet template des protéines de formes différentes. Dans des conditions particulières, nous avons aussi pu produire des nanoparticules fluorescentes d'or de 2-6 nm de diamètre. Par ailleurs, des paires de protéines α-Repins, sélectionnées par évolution dirigée pour leur affinité mutuelle, ont été conjuguées à des populations différentes de nanoparticules. L'auto-assemblage massif et spontané des nanoparticules est alors induit lors du mélange de population portant des protéines complémentaires. Ces résultats constituent la première étape de la construction d'une approche généralisation dans laquelle des protéines artificielles peuvent être conçues et produites pour contrôler la structure cristalline et la morphologie de particules plasmoniques ou bien induire leur couplage spécifique avec d'autres particules fonctionnelles permettant ainsi d'envisager la construction d'architectures colloïdales plasmoniques complexes.Confinement and guiding of light energy at nanoscale in devices composed of colloidal building blocks, requires a precise control of (i) the morphology of the nanoparticles, (ii) their spatial organization into larger scale architectures and (iii) the coupling between plasmonic colloid and optically active. This thesis work explores new synthetic approaches, including bio-inspired ones, of these three challenges. As a first insight, we have employed biomineralization principles to tune the plasmon-fluorophore coupling in order to control the fluorescence enhancement. The fluorescence properties of a well-organized, finite ensemble of porphyrins called J-aggregates is modulated by the templated encapsulation of silica of controlled thickness, in the range of 2 ± 1 nm to 12 ± 1 nm, and its decoration with Au and Ag nanoparticles. Porphyrin J-aggregates act as templates for the silica mineralization, while the inorganic shell first provides a mechanical stability and also becomes a template for the specific binding Au or Ag nanoparticles with a dielectric spacing for optimal exciton-plasmon coupling. The metal-enhanced fluorescence can be optimized exceeding 400% and about 200% with the conjugation of Ag and Au nanoparticles on templated J-aggregates respectively. Such bottom-up templated constructions could contribute to the design of optical probes for sensing and imaging applications but also to the efficient integration of molecular absorbers and emitters into plasmonic devices for optical information processing. In the second part we explored new methods to control the morphology of metallic nanoparticles, and their self-assembly using artificial proteins called a-Repins. The main advantages of these artificial proteins are there high thermal stability and their well-defined and robust 3D structure, which can be modulated by concatenation of a portion of the sequence while preserving some variability for some amino acid positions. The direct chemical reaction of these a-Rep proteins with Au sol results in the particles of spherical triangular, rod and wire shaped morphology where proteins acts as a template. Also fluorescent nanoclusters of size 2-6nm has been obtained when a-Rep proteins are used as a stabilizing agents. Finally, pairs of a-Rep proteins with mutual affinity have been selected by phage display and conjugated with different population of nanoparticles. Massive and spontaneous self-assembly was triggered by mixing these two particle particles populations bearing complementary proteins. These results are the first steps of the development of a versatile biomolecular toolbox in which artificial proteins can be fully designed to either control the crystallographic structure and morphology of plasmonic nanoparticles or induce their specific coupling to other functional nanoparticles therefore allowing to construct plasmonic and metamaterials colloidal architectures

Infrared thermochromic antenna composite for self-adaptive thermoregulation

Self-adaptive thermoregulation, the mechanism living organisms use to balance their temperature, holds great promise for decarbonizing cooling and heating processes. The functionality can be effectively emulated by engineering the thermal emissivity of materials to adapt to background temperature variations. Yet, solutions that marry large emissivity switching (${\Delta}\epsilon$) with scalability, cost-effectiveness and design freedom are still lacking. Here, we fill this gap by introducing infrared dipole antennas made of tunable thermochromic materials. We demonstrate that non-spherical antennas (rods, stars and flakes) made of vanadium-dioxide can exhibit a massive (~200-fold) increase in their absorption cross-section as temperature rises. Embedding these antennas in polymer films, or simply spraying them directly, creates free-form thermoregulation composites, featuring an outstanding ${\Delta}\epsilon\sim0.6$ in spectral ranges that can be tuned at will. Our research paves the way for versatile self-adaptive heat management solutions (coatings, fibers, membranes and films) that could find application in radiative-cooling, heat-sensing, thermal-camouflage, and other

Structural flexibility and selective guest accommodation in two Cu<SUP>II</SUP> metal-organic coordination frameworks

Two metal–organic coordination frameworks of CuII, [Na2Cu(2,4‐pyrdc)(H2O)(&#x003BC;‐OH2)2]n (1) and {[Cu(2,5‐pyrdc) (NH3)](2H2O)}n (2) (2,4‐pyrdc = pyridine‐2,4‐dicarboxylate; 2,5‐pyrdc = pyridine‐2,5‐dicarboxylate), were synthesized and structurally characterized. The structure of compound 1 was known and shows that Cu(2,4‐pyrdc)2(H2O) functions as a metalloligand and is linked to two different NaI atoms to form a 3D heterometallic CuII–NaI framework. The single crystals of compound 2 were obtained from aqueous ammoniacal solution and crystallize in the triclinic (P$\bar {1}$equation image) crystal system. Compound 2 is a 2D sheet consisting of two different CuII 1D chains bridged by a 2,5‐pyrdc ligand. Stacking of the 2D sheets results in a 3D supramolecular host with 1D water‐filled channels. Both frameworks are highly thermally stable and exhibit reversible structural transformation upon removal of the metal‐bound water and NH3 molecules for 1 and 2, respectively. Sorption studies reveal that desolvated frameworks 1′ and 2′ both behave nonporous to N2. However, 1′ exhibits structural transformation and hysteretic stepwise sorption of H2O and MeOH molecules, but THF and C6H6 molecules are not adsorbed. Similarly, H2O and MeOH molecules are easily adsorbed in 2′, but THF and C6H6 molecules are not. Such high selectivity in 1′ and 2′ was correlated to the smaller pore aperture and specific host–guest interaction conferred by the unsaturated Lewis acidic sites on the pore surfaces and the Lewis basic adsorbates. Low‐temperature magnetic study of 2 revealed that theCuII atoms are antiferromagnetically coupled, with J = –1.45 cm-1 and g = 2.01

Tuning the Optical Coupling between Molecular Dyes and Metal Nanoparticles by the Templated Silica Mineralization of J‑Aggregates

Supramolecular porphyrin aggregates are used as a template for the higher-order assembly of fluorophore–dielectric–metal hybrid nanostructures in which the optical properties of the molecules are modulated by the finely tuned coupling to localized plasmons. First, J-aggregates are encapsulated inside a dielectric silica shell of well-controlled thickness, which reinforces mechanically the template and serves as a precise optical coupling spacer. The silicified J-aggregates are then decorated with gold or silver nanoparticles. UV–visible and fluorescence spectroscopies show that the presence of metal nanoparticles induces a marked enhancement of the J-aggregate fluorescence when the silica thickness is tuned to 7–12 nm, whereas a significant quenching is measured when the dielectric thickness is sub-2 nm. Interestingly, the enhancement is maximized when oxidized silver nanoparticles are placed very close to the J-aggregates

Universal Theory of Light Scattering of Randomly Oriented Particles: A Fluctuational-Electrodynamics Approach for Light Transport Modeling in Disordered Nanostructures

Disordered nanostructures are commonly encountered in many nanophotonic systems, from colloid dispersions for sensing to heterostructured photocatalysts. Randomness, however, imposes severe challenges for nanophotonics modeling, often constrained by the irregular geometry of the scatterers involved or the stochastic nature of the problem itself. In this Article, we resolve this conundrum by presenting a universal theory of averaged light scattering of randomly oriented objects. Specifically, we derive expansion-basis-independent formulas of the orientation-and-polarization-averaged absorption cross section, scattering cross section, and asymmetry parameter, for single or a collection of objects of arbitrary shape. These three parameters can be directly integrated into traditional unpolarized radiative energy transfer modeling, enabling a practical tool to predict multiple scattering and light transport in disordered nanostructured materials. Notably, the formulas of average light scattering can be derived under the principles of fluctuational electrodynamics, allowing the analogous mathematical treatment to the methods used in thermal radiation, nonequilibrium electromagnetic forces, and other associated phenomena. The proposed modeling framework is validated against optical measurements of polymer composite films with metal-oxide microcrystals. Our work may contribute to a better understanding of light-matter interactions in disordered systems, such as plasmonics for sensing and photothermal therapy, photocatalysts for water splitting and CO2 dissociation, photonic glasses for artificial structural colors, and diffuse reflectors for radiative cooling, to name just a few

Multimodal Plasmonics in Fused Colloidal Networks

International audienceHarnessing the optical properties of noble metals down to the nanometer-scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon (SP) properties must be controlled with a challenging high level of precision. Here, we demonstrate that ultimate lateral confinement and delocalization of SP modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the SP modes associated with the colloidal superstructures are evidenced by performing monochromated electron energy loss spectroscopy with a nanometer-sized electron probe. We prepare the metallic bead strings by electron beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphology and crystallinity but develop very low energy SP modes that are capable of supporting long range and spectrally tunable propagation in nanoscale waveguides

Nanoparticles Self-Assembly Driven by High Affinity Repeat Protein Pairing

International audienceProteins are the most specific yet versatile biological self-assembling agents with a rich chemistry. Nevertheless, the design of new proteins with recognition capacities is still in its infancy and has seldom been exploited for the self-assembly of functional inorganic nanoparticles. Here, we report on the protein-directed assembly of gold nanoparticles using purpose-designed artificial repeat proteins having a rigid but modular 3D architecture. αRep protein pairs are selected for their high mutual affinity from a library of 10(9) variants. Their conjugation onto gold nanoparticles drives the massive colloidal assembly of free-standing, one-particle thick films. When the average number of proteins per nanoparticle is lowered, the extent of self-assembly is limited to oligomeric particle clusters. Finally, we demonstrate that the aggregates are reversibly disassembled by an excess of one free protein. Our approach could be optimized for applications in biosensing, cell targeting, or functional nanomaterials engineerin

Directed evolution of artificial repeat proteins as habit modifiers for the morphosynthesis of (111)-terminated gold nanocrystals

International audienceNatural biocomposites are shaped by proteins that have evolved to interact with inorganic materials. Protein directed evolution methods which mimic Darwinian evolution have proven highly successful to generate improved enzymes or therapeutic antibodies but have rarely been used to evolve protein-material interactions. Indeed, most reported studies have focused on short peptides and a wide range of oligopeptides with chemical binding affinity for inorganic materials have been uncovered by phage display methods. However, their small size and flexible unfolded structure prevent them from dictating the shape and crystallinity of the growing material. In the present work, a specific set of artificial repeat proteins (αRep), which exhibit highly stable 3D folding with a well-defined hypervariable interacting surface, is selected by directed evolution of a very efficient home-built protein library for their high and selective affinity for the Au(111) surface. The proteins are built from the extendable concatenation of self-compatible repeated motifs idealized from natural HEAT proteins. The high-yield synthesis of Au(111)-faceted nanostructures mediated by these αRep proteins demonstrates their chemical affinity and structural selectivity that endow them with high crystal habit modification performances. Importantly, we further exploit the protein shell spontaneously assembled on the nanocrystal facets to drive protein-mediated colloidal self-assembly and on-surface enzymatic catalysis. Our method constitutes a generic tool for producing nanocrystals with determined faceting, superior biocompatibility and versatile bio-functionalization towards plasmon-based devices and (bio)molecular sensors