Yttrium vanadate particles doped with europium are studied for their applications as biomolecule labels. Two parts of
our work will be presented. The first concerns the thermal treatment of particles incorporated in a silica matrix. After
annealing at 1000°C and redispersion in water by dissolution of the silica matrix, the structural and optical properties are
greatly improved: without any modification of size, the obtained nanoparticles appear as perfect single crystals of 33 nm
and have the same emission properties as the bulk material, with a quantum yield and emission lifetime increasing up to
40% and 0.8 ms. The second aspect concerns the detection of single nanoparticles and their emission properties as
compared to an ensemble of nanoparticles.
We report on the single-particle properties of lanthanide-ion doped oxide nanoparticles. We have demonstrated that their size can be accurately determined from their luminosity. The optically determined size distribution is in very good agreement with the distribution obtained from transmission electron microscopy (TEM). We also showed that the photobleaching of these nanoparticles is related to a reduction process and that we can use it to sense in a concentration-dependent manner the presence of an oxidant like H<sub>2</sub>O<sub>2</sub>. Finally, we propose a way to perform nanoparticle-protein coupling and to determine the protein-nanoparticle ratio at the single-particle level.
We have demonstrated fluorescence resonance energy transfer (FRET) between lanthanide-ion doped oxide nanoparticles acting as donors and organic acceptor molecules (Cy5). Due to the long nanoparticle lifetime and the large Stokes shift between nanoparticle absorption and emission, unambiguous and precise FRET measurements can be performed despite the presence of large free acceptor oncentrations. We determined FRET efficiencies as a function of Cy5 concentration which are in very good agreement with a multiple acceptor-multiple donor calculation.
Lanthanide-ion doped oxide nanoparticles were functionalized for use as fluorescent biological labels. These nanoparticles are synthesized directly in water which facilitates their functionalization, and are very photostable without emission intermittency. Nanoparticles functionalized with guanidinium groups act as artificial toxins and specifically target sodium channels. They are individually detectable in cardiac myocytes, revealing a heterogeneous distribution of sodium channels. Functionalized oxide nanoparticles appear as a novel tool particularly well adapted to long-term single-molecule tracking.