Bioinspired Approaches in Nanoplasmonics

Abstract : 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 α-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 α-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 α-Rep proteins are used as a stabilizing agents. Finally, pairs of α-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.
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Gurunatha Kargal Laxminarayana. Bioinspired Approaches in Nanoplasmonics. Other. Université Toulouse III Paul Sabatier (UT3 Paul Sabatier), 2012. English. ⟨tel-01794607⟩

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