Ultrafine nanoparticles comprising a functionalized polyorganosiloxane matrix and including metal complexes; method for obtaining same and uses thereof in medical imaging and/or therapy

A method for producing a nanoparticle having a diameter from 1 to 8 nm, wherein said method comprises:

• a) synthesizing a metallic oxide core comprising a cationic form Mn+(n=2 to 6) selected from the group consisting of a rare earth element, an actinide element and a transition element, optionally doped with a dopant (D), selected from the group consisting of a rare earth element different from M, an actinide and/or a transition element;
• said synthesizing comprises mixing a base with a salt of M dissolved in a solvent optionally selected from the group comprising alcohols;
• b) coating of the core from (a) with polyorganosiloxane (POS) comprising employing a sol/gel technique for hydrolysis-condensation of silicic species and alkoxysilanes, in the presence of a base or of an acid;
• c) functionalizing the coated core from (b) comprising bringing said coated core from (b) into contact with a precursor of chelating agent C1 that is capable of complexing a cationic form Mn+, and optionally Dm+(n=2 to 6), thereby obtaining functionalized precursor nanoparticle of a diameter d0;
• d) purification of the functionalized precursor nanoparticle of diameter d0, optionally by tangential filtration, dialysis and/or by precipitation/washing;
• e) dissolving the cores M of the functionalized nanoparticle from (c) by placing said functionalized nanoparticle in aqueous solution, so that the diameter d0 of said precursor nanoparticle is reduced to a value from 1 to 8 nm, thereby obtaining a nanoparticle with a diameter from 1 to 8 nm;
• and
• f) optionally adding a cationic salt intended to be at least partly complexed by said chelating agent C1;
• wherein (c), (d), (e), (f) can be carried out in a different order or at the same time.