Radiolabelling of engineered nanoparticles – alternative strategies for Ag0-NP, TiO2-NPs and CNTs

As nanotechnology increasingly finds its way into everyday applications the risk assessment of a potential nanoparticle (NP) release into the environment becomes mandatory. Though, NPs are notoriously difficult to trace in such complex environments as the geosphere, ground and surface waters or organisms, especially at the predicted low concentrations that nevertheless might be environmentally relevant. Radiolabeling of NPs provides a possibility to overcome this problem. However, radiolabeling itself bears the danger of changing the particle properties, leading to uncertainties in the interpretation of experimental results. We here present radiolabelling strategies for TiO2, Ag0 nanoparticles and carbon nanotubes (CNTs) that were developed with a minimum of NP property alteration in mind.

TiO2 and Ag0 NPs were radiolabeled using an in-diffusion technique resulting in the incorporation of radionuclides of the respective element in the NPs. Briefly, radionuclide stock solutions containing 45Ti or 110mAg were applied to dry nanoparticle powder followed by a low temperature annealing for diffusive introduction of the radionuclides into the NPs. A stable radiolabeling was achieved with no significant change in particle properties detectable in the range of our experimental conditions.

CNTs were radiolabelled using the one-pot Iodogen reaction for introduction of radioactive iodine 125/131I onto the CNT side wall. The radiolabel proved to be stable in the absence of light and no changes of the particle properties could be measured. The potential employment of 124I opens the possibility for positron emission tomography studies and therefore the localisation of radiolabeled CNTs in complex matrices such as rock materials.