CdSe-core, ZnS-capped semiconductor nanoparticles - quantum dots (QDs) - have been at the forefront of biomedical nanotechnology research thanks to their unique optical Η photophysical properties. In the present study the impact of the particle coating and size on their in vivo fate after intravenous (IV) injection into mice was studied by fluorescence methods. For this study, we compared organ-selective biodistribution and elimination routes of synthesized QDs coated with 3-mercaptopropionic acid (QD MPA) and commercially available Qtracker 705 nontargeted quantum dots with poly(ethylene glycol) coating (QD PEG). We observed primary accumulation of these QDs in lung. Experiments demonstrated that QD MPA and QD PEG have both remained fluorescent in lung after at least 24 hours postinjection. Moreover, QDs was seen to deposit mainly in liver, spleen, kidney and lymph nodes. We also concluded that QDs MPA and QDs 705 are both sequestered and not excreted with feces or urine.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.