Luminescent hybrid nanoparticles with a paramagnetic Gd2O3 core were applied as contrast agents for both in vivo fluorescence and magnetic resonance imaging. These hybrid particles were obtained by encapsulating Gd2O3 cores within a polysiloxane shell which carries organic fluorophores and carboxylated PEG covalently tethered to the inorganic network. Longitudinal proton relaxivities of these particles are higher than the positive contrast agents like Gd-DOTA which are commonly used for clinical magnetic resonance imaging. Moreover these particles can be followed up by fluorescence imaging. This study revealed that these particles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in lungs and liver.

Doubly luminescent core/shell structure nanoparticles were synthesized for biological detection. In the first step gadolinium oxide (Gd 2 O 3 ) core doped with the luminescent Tb 3+ ions was obtained by applying, with modifications, the polyol route, which allows direct precipitation of oxide nanoparticles in a polyalcohol medium. The presence of Tb 3+ ions in the Gd 2 O 3 crystalline matrix confers attractive optical properties for long-term studies and multilabeling such as a high photostability and narrow emission bands. The water sensitivity of these particles, which is detrimental for the Tb ion's luminescence, was overcome by embedding the oxide core in a functionalized polysiloxane shell prepared by hydrolysis condensation of a mixture of APTES and TEOS. This protective layer allows the dispersion of the particles in aqueous solution without loss of luminescence intensity. Moreover, the luminescence of polysiloxanecoated Gd 2 O 3 nanoparticles is more intense than that in the case of the naked Gd 2 O 3 core. Due to the presence of amino groups, organic dyes and biotargeting groups (nucleic acid, biotin, streptavidin) were covalently linked to the polysiloxane network. These particles are efficient for detection of biomolecules whose presence is revealed by the high fluorescence of organic dyes and/or the photostable Tb 3+ ion's luminescence.

The use of gold nanoparticles as biological probes requires the improvement of colloidal stability. Dihydrolipoic acid (DHLA), a dithiol obtained by the reduction of thioctic acid, appears therefore very attractive for the stabilization and the further functionalization of gold nanoparticles because DHLA is characterized by a carboxylic acid group and two thiol functions. The ionizable carboxylic acid groups ensure, for pH > or = 8, the water solubility of DHLA-capped gold (Au@DHLA) nanoparticles, prepared by the Brust protocol, and the stability of the resulting colloid by electrostatic repulsions. Moreover almost all DHLA, adsorbed onto gold, adopts a conformation allowing their immobilization by both sulfur ends. It is proved by sulfur K-edge X-ray absorption near edge structure spectroscopy, which appears as an appropriate tool for determining the chemical form of sulfur atoms present in the organic monolayer. Such a grafting renders the DHLA monolayers more resistant to displacement by dithiothreitol than mercaptoundecanoic acid monolayers. The presence of DHLA on gold particles allows their functionalization by the electroluminescent luminol through amine coupling reactions assisted by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. As a luminol-functionalized particle is nine times as bright as a single luminol molecule, the use of the particles as a biological probe with a lower threshold of detection is envisaged.