A novel method for synthesis of 56Co-radiolabelled silica nanoparticles

A method for synthesis of radiolabelled amorphous silica nanoparticles is presented. The method is based on the well-known Stober process with the exception that Co-56 radiotracer is introduced into one of the precursor materials prior to the initiation of the nanoparticle synthesis. The Co-56 was prepared by proton irradiation of an iron foil, followed by dissolution in hydrochloric acid and Co-56/Fe radiochemical separation. In order to determine the residual Fe in the Co-56 radiotracer solution, ICP-MS measurements were performed. Nanoparticles in the size range 20-100 nm were synthesised and characterised by gamma spectrometry, ICP-MS, XRD, DLS, and Zeta potential measurement. It was shown that the size and Zeta potential of the nanoparticles was roughly the same following synthesis with or without added Co-56, and in both cases, the structure was that of amorphous silica. It was found that 99.5 % of the Co-56 was bound into the nanoparticles during synthesis, and centrifugation experiments confirmed that the radiolabels were stably incorporated into the silica matrix.