Small Bioactivated Magnetic Quantum Dot Micelles

Many biological processes are activated through nondiffusive distribution of biomolecules in biological systems. To both label and induce such gradients of proteins, our strategy is to prepare bioactivated nanometer-sized nanoparticles combining magnetic and fluorescent properties. Here, bioactivated fluorescent magnetic micelles with an hydrodynamic diameter of around 25 nm are obtained by coencapsulation of both hydrophobic CdSe/ZnS quantum dots (QD) and γ-Fe 2 O 3 nanocrystals into a liquid crystal phase composed of synthetic amphiphilic PEG gallates derivatives bearing a terminal active chemical group. The present method permits to both functionalize and solubilize magnetic and fluorescent nanocrystals into the same micelle starting from a condensed hybrid hexagonal phase. Reactive groups, such as amine, carboxylic acid, and biotin, are introduced on the surface of the nanoparticle with a controlled molar ratio. The magnetic and fluorescence properties are demonstrated by complementary techniques such as SQUID experiments and fluorescence spectrometry. The molar QD/γ-Fe 2 O 3 ratio between quantum dots and iron oxide nanocrystals is optimized to the value 1/1 to get a fluorescence quantum yield of 15% and to keep magnetic properties. The fluorescent magnetic micelles can move and be trapped under a magnetic field gradient in a few minutes. Finally, the synthesis of various gallate ligands bearing a biotin terminal group permits to bioactivate the nanocrystals as demonstrated by the selective binding of the micelles to agarose Streptavidin micrometer-range beads. These multifunctional fluorescent and magnetic nanoparticles of small size can target any biomolecule through biotin/streptavidin or amide covalent binding and could be used to manipulate and vary its spatial distribution under a magnetic gradient field.