The effect of fluorination of zinc oxide nanoparticles on evaluation of their biodistribution after oral administration

Monitoring of the behavior of metal nanoparticles in the body following exposure is very important for investigation of the physiological fates and safety of these nanoparticles. In this study, we investigated the behavior and accumulation of nano-scaled ZnO (20 nm) and submicro-scaled ZnO (100 nm) particles in organic tissues after oral administration using PET imaging. Both types of ZnO nanoparticle (20 or 100 nm) were labeled with the radionuclide ¹⁸F in high yield via click reaction. ¹⁸F labeling on the ZnO nanoparticles was maintained stably in simulated gastric fluid (pH 1.2) for 7 h. PET images indicated that ¹⁸F and ¹⁸F-ethoxy azide showed radioactivity in the bone and bladder 3 h after oral administration, whereas radioactivity for 18F-labeled ZnO nanoparticles was seen only in the gastrointestinal (GI) tract. At 5 h post-administration, biodistribution studies demonstrate that 18F accumulated in the bone (10.19 ± 1.1%ID g ^-1) and 18F-ethoxy azide showed radioactivity in the bone (7.55 ± 0.6%ID g ^-1), liver, and brain (0.94 ± 0.3%ID g ^-1). Unlike 18F and ¹⁸F-ethoxy azide, ¹⁸F- labeled ZnO nanoparticles showed radioactivity in the lung, liver and kidney including the GI tract. Submicro-scaled 18F-labeled ZnO nanoparticles (100 nm) showed stronger radioactivity in the liver and kidney compared to nano-scaled ¹⁸F-labeled ZnO nanoparticles (20 nm). In conclusion, PET imaging has the potential to monitor and evaluate the behavior of ZnO nanoparticles absorbed in organic tissues following oral exposures.