TECHNICAL NOTE Synchrotron X-ray 2D and 3D elemental imaging of CdSe/ZnS quantum dot nanoparticles in Daphnia magna Brian P. Jackson & Heather E. Pace & Antonio Lanzirotti & Randy Smith & James F. Ranville Received: 5 February 2009 / Revised: 19 March 2009 / Accepted: 23 March 2009 / Published online: 2 April 2009 # Springer-Verlag 2009 Abstract The potential toxicity of nanoparticles to aquatic organisms is of interest given that increased commerciali- zation will inevitably lead to some instances of inadvertent environmental exposures. Cadmium selenide quantum dots (QDs) capped with zinc sulfide are used in the semicon- ductor industry and in cellular imaging. Their small size (<10 nm) suggests that they may be readily assimilated by exposed organisms. We exposed Daphnia magna to both red and green QDs and used synchrotron X-ray fluores- cence to study the distribution of Zn and Se in the organism over a time period of 36 h. The QDs appeared to be confined to the gut, and there was no evidence of further assimilation into the organism. Zinc and Se fluorescence signals were highly correlated, suggesting that the QDs had not dissolved to any extent. There was no apparent difference between red or green QDs, i.e., there was no effect of QD size. 3D tomography confirmed that the QDs were exclusively in the gut area of the organism. It is possible that the QDs aggregated and were therefore too large to cross the gut wall. Keywords Nanoparticles . Quantum dots . Synchrotron XRF . Elemental imaging . Tomography Introduction Quantum dots (QDs) such as CdS, CdSe, and ZnS are semiconductor particles with a typical size of 1–10 nm. They have the property of being intensely fluorescent, rendering them extremely useful in many applications. For example, they are used in optical and electronic applications (LED systems and flat screen computer displays) and have utility in medical applications such as cellular imaging [1] and potentially in fighting cancer [2, 3]. Since QDs have great utility in many markets, it is inevitable that future mass production/use will result in some portion of the materials being released to the environment. The current level of understanding specifically on the toxicology of quantum dots has been reviewed [4]. The review lists QD size, charge, concentration, outer surface cap and surface functional groups, and oxidative, photolyt- ic, and mechanical stability as determining factors in QD toxicity. It further points out that exposure through environmental media is a concern and that exposure will depend on partitioning of QDs between air, water, and solid phases, which will be a function of the environmental media and the QD characteristics. One type of quantum dot, CdSe, has been shown to have cytotoxic effects ([4–7] and references therein). Kirchner et al. [5] found that CdSe was Anal Bioanal Chem (2009) 394:911–917 DOI 10.1007/s00216-009-2768-y B. P. Jackson (*) Trace Element Analysis Laboratory, Departments of Earth Sciences and Chemistry, Dartmouth College, Hanover, NH 03755, USA e-mail: BPJ@dartmouth.edu H. E. Pace : J. F. Ranville Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401, USA A. Lanzirotti Consortium for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA R. Smith National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973, USA