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Oxide nanoparticles (NPs) doped with rare-earth ions are tested for applications as nanomarkers in biology. The aim of this study was to investigate the intra-organism distribution of ZnO nanoparticles doped with europium following gastric gavage (IG) in mice. The study is an example of the innovative and comprehensive methodology in research on biodistribution of nanomaterials in the body. We used quantitative (AAS) and imaging (scanning cytometry, confocal microscope) methods of assessing the distribution of rare-earth doped ZnO nanoparticles in the living organism. Visualization of these processes in the body was possible because of high fluorescence yield of europium. Imaging methods applied in this study (scanning cytometry and confocal microscopy) seem to be crucial for understanding the uptake and distribution patterns of nanoparticles within the living organism.

First generation of biomarkers (fluorescence labels) is based on organic dyes. To replace them nanoparticles (NPs)/quantum dots (QDs) of highly fluorescent CdTe-, CdS- and CdSe-based biomarkers were introduced. Despite the fact that these NPs show some advantageous properties, their use is limited by blinking, spectral diffusion of emission and use of cadmium, which should be avoided in the case of biological and medical applications. This fact motivated us to develop new generation of biomarkers using biocompatible oxides - ZnO, ZnAl 2 O 4 and ZrO 2 . Their emission is activated by doping with rare earth (RE) ions.