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Core-shell and Doped Silicate Nanoparticles Prepared by a Spray-drying Process for the Development of Biological Luminescent Tracers
Cécile Philippot, Fabien Dubois, Adrien Bourdolle, Olivier Maury, Bruno Boury, Chantal Andraud and Alain Ibanez

Using a spray-drying process, we developed a versatile, one step synthesis, of two-photon luminescent silicate nanoparticles. The formation of the nanoparticles is based on the controlled drying of sol-gel droplets in a heated laminar flux inside a tubular furnace. Two types of nanoparticles were prepared, hybrid core-shell nanoparticles and silicate nanoparticles doped with an europium(III) complex. In the first case of hybrid (organic-silicate) coreshell nanoparticles the fast evaporation of THF solvent enhance the polycondensation of the silicate network in the droplets, particularly at their surface. This induces first the formation of a silicate crust followed, at the end of the solvent evaporation, by the nucleation and growth of the organic dye in the core of the resulting dried nanoparticles. We studied the different physical and chemical parameters that influence the perfect and reproducible control of the confined nucleation and growth of dye nanocrystals in the sol-gel droplets. In the second case, silicate nanoparticles were doped with a functionalized tris-dipicolinate europium complex, which presents an important two-photon absorption cross section but exhibits a weak stability in water due to the dissociation of the complex. Two different compositions of the starting sols were tested to adjust the hydrophilic character of the nanoparticles and to avoid the dissociation of the europium complexes in water by closing the porosity of the silicate shell.

Keywords: Spray-drying process, Silicate nanoparticles, Sol-gel, Two-photon luminescence, lanthanide-complexes, core-shell nanoparticles

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