The present invention relates to novel nanoparticles which can be advantageously used in the health sector as diagnostic and/or therapeutic agents. Nanoparticles of the invention comprise a metallic material at least partly covered with an hafnium oxide material or embedded therein. When compared to existing products, these nanoparticles offer a remarkable benefit over risk ratio. Specifically, these nanoparticles potentiate the efficiency of known metallic nanoparticles. Indeed, they retain the metal intrinsic properties and are now in addition safely usable in a mammal, in particular in a human being. The invention also relates to methods for producing said nanoparticles, to compositions containing same, and to uses thereof.
