Radiolabelling of engineered nanoparticles – different strategies for Ag0-NP, TiO2-NP and MWCNTs

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 (NPs) 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 present here two different radiolabelling strategies for Ag0-NP, TiO2-NP and MWCNTs.

Both strategies involve proton bombardment using a cyclotron and cause the incorporation of radioactive isotopes inside the NPs. The first option is to directly activate the NPs by proton irradiation, which proved useful for MWCNTs and TiO2-NP. 12C gets activated using a (p,3d) nuclear reaction to 7Be while 48Ti gets activated to 48V by a (p,n) reaction.
The second option, which is generally adoptable for NPs that do not show useful nuclear reactions, is to mix the NP powder with a lithium containing compound like LiH and irradiate it to create 7Be out of 7Li via a (p,n) reaction. The recoil of the 7Be from the nuclear reaction causes the incorporation of the radiotracer into the structure of the NP.
The methods were tested for labelling yield, achievable activity concentration, pH-dependent stability of the labeling and the influence on NP-properties. Data thus obtained enables the selection of a radiolabelling method appropriate for different experimental conditions.
48V labeled TiO2-NPs were successfully employed to study the NP release out of surface coatings not measurable using conventional methods.