Organic@silicate core-shell nanoparticles and garnet-type oxide nanocrystals as luminescent tracers for biophotonics
Résumé
We will present two different types of luminescent nanoparticles (NPs) for the development of in vivo tracers, both excited in the biological window at around 800 nm: fluorescent molecular nanocrystals grown in the core of silicate NPs and luminescent oxide nanocrystals (garnet type doped with Nd3+) for nanothermometry. We will present first the elaboration and functionalization of hybrid organic-inorganic core-shell NPs to be used for two-photon deep tissue imaging of tumor vascularization. These core-shell NPs, which comprise an organic dye nanocrystal core (40-50 nm) surrounded by a silicate crust, are synthesized using an original spray-drying method. This process is based on the confined nucleation and growth of organic nanocrystals in silicate sol-gel NPs through the fast drying of sprayed droplets containing silicate oligomers, organic dye and solvent under a laminar air flux at 150-200 °C. This one-step process is monitored thanks to the both control of silicate network polycondensation and dye nanocrystallization, which occur simultaneously. We selected dyes arising from a specific molecular engineering (Y. Bretonnière and C. Andraud ENS-Lyon) exhibiting intense orange-red fluorescence emissions in the crystal-state to work close to the biological window. On the other hand, we developed a new synthesis method of garnet-type nanocrystals (Nd3+ doped YAG :Y3Al5O12) based on solvothermal process coupled with external pressure. We succeeded in obtaining nm-sized single-crystals in the range 30 to 200 nm. Their high crystalline quality allowed to observe intense Nd3+ luminescence in the near IR: excitation at 808 nm (4I9/2 → 4F5/2) with two emission bands at around 938 and 945 nm (4F3/2 → 4I9/2). The reproducible and significant evolution of luminescence intensity of these two emissions versus temperature, between 20 and 50°C, allows us to consider very promising developments for in vivo nanothermometry applications, in collaboration with the group of F. Vetrone (INRS and Univ. Montréal).