Measuring at relevant concentrations - radiolabelling as a versatile tool for sensitive nanoparticle detection

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories, a careful risk assessment of their release into the environment becomes mandatory. However, the monitoring of nanoparticles in such complex natural systems as geological formations or ground water is nearly impossible using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research.
We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, Silica and TiO₂ nanoparticles. The labelling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labelling utilizing the recoil of a nuclear reaction to introduce a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [^105/110mAg]Ag, [^124/125/131I]CNTs, [⁴⁸V]TiO₂, [⁷Be]MWCNT, [⁷Be]SiO₂, [^44/45Ti]TiO₂, etc.. The methods are adaptable for a wide range of other nanoparticles. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary.
Using our methods one can radiolabel commercial nanoparticle samples for sensitive detection in environmentally relevant trace concentrations.