Quantitative determination of the biodistribution of nanoparticles: could radiolabelling be the answer?

The increased incorporation of NPs in everyday products has raised many concerns related to potential toxicological effects derived from long term workplace, environmental or consumer exposure. On the other hand, the potential applications of NPs in the biomedical field require a reliable and convenient strategy for their pharmacological evaluation. In both scenarios, a method to quantitatively track the NPs after incorporation or administration into living organisms is highly desirable. In this context, labelling NPs with positron or gamma emitters may constitute an ideally suited technique to track NPs in vivo using nuclear imaging techniques, i.e. positron emission tomography (PET) or single photon emission computerised tomography (SPECT). Attractively, these imaging modalities are considered as minimally invasive (only the administration of the labelled species is required) and allow time-resolved and quantitative determination of the amount of labelled species within the organism. In addition, due to the high penetration capacity of gamma rays, they can be easily translated from small experimental animals to humans without significant tissue-attenuation related issues. Finally, due to their intrinsic unparalleled sensitivity, only small amounts of the labelled material need to be administered; thus, pharmacological, toxicological and/or undesired side effects can usually be minimised. It should be noted however, that nuclear imaging techniques require a certain activity concentration to be viable, and where biodistribution studies over several days, weeks, or even months are required, or in cases where extremely low concentrations of NPs need to be detected, non-imaging methods based on radioactivity measurements on individual organs constitute the most accurate approach in animal experiments.JRC.I.4-Nanobioscience