Radiolabeling of nanoparticles as a versatile tool in safety research

Identification and quantification of nanoparticulate materials in living and non-living media is mandatory for a thorough nanosafety research. However, the online and in-situ monitoring of nanoparticles in such complex natural systems as soil, natural waters, plants, sewage sludge, etc. is highly challenging, especially at environmentally relevant concentrations. Radiolabeling offers a robust method for these complex studies within a wide range concentration of nanoparticles even in the presence of background concentrations of the respective elements.

Depending on the nature of the nanoparticle and the process of interest we applied different methods for the radiolabeling of common nanoparticles, like 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 labeling utilizing the recoil of a nuclear reaction to implant a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles.

For our recent studies we produced [¹⁰⁵Ag]Ag, [^110mAg]Ag, [⁴⁴Ti]TiO₂, [⁴⁵Ti]TiO₂, [⁴⁸V]TiO₂, [⁶⁴Cu]CuS, [⁶⁴Cu]SiO₂, [⁶⁵Zn]CdSe/ZnS, [¹²⁴I]CNTs, [¹²⁵I]CNTs, [¹³¹I]CNTs, [⁷Be]MWCNT, [¹³⁹Ce]CeO₂ and [¹⁹⁴Au]Pt nanoparticles (including radiolabeled commercial nanoparticle samples). Due to the choice of the used radionuclide (half-life, decay-mode) and the activity concentrations it was possible to enable different detection methods and time scales for the investigations. All these methods go along with a careful characterization of the radiolabeled nanoparticles in respect of the radiolabeling stability and nanoparticle properties.

The radiolabeled nanoparticles can easily be detected down to ng/L range and have been successfully used in investigations of the uptake of nanoparticles in plants, the distribution and mobility of nanoparticles in sewage sludge, fate of nanoparticles in wastewater treatment processes and in release studies.