Concept of quantitative nanoparticle biokinetics. Nanoparticles (NP) are administered at time t = 0. From this time point on, the entire urinary and fecal excretions are collected separately. Animals are euthanized at times t1, t2, t3, etc., and organs and tissues of interest as well as the entire remaining carcass are sampled (100% balanced sampling). Samples require special preparation before chemical analysis, e.g. by inductive-coupled-plasma mass spectroscopy (ICP-MS). When nanoparticles are radio-labeled, samples will be analyzed directly, without any further preparation. Reprinted with permission from .