To this end, we have synthesized monodisperse boron-rich silica nanoparticles, either by a sol-gel process involving boric acid and alkoxysilanes, or by surface-initiated atom-transfer radical polymerization of boron-containing monomers. Several fluorone-based dyes (fluorescein, rhodamines) were also incorporated within the silica matrix, resulting in a strong and stable fluorescence which allows direct imaging of the particles by confocal microscopy. Further functionalization of such particles with tumor-targeting moieties such as integrins is currently under investigation.