Spectral insights into the transformation and distribution of CdSe quantum dots in microorganisms during food-chain transport.

The discharge of engineered nanomaterials (ENMs) into environment is raising widespread concern not only due to their direction bio-toxicity but also their bio-concentration and bio-magnification through food web. However, the transformation and distribution of ENMs during food-chain transport are poorly understood, due to lack of accurate, reliable analytical methods. In this study, by using a suite of advanced spectrum techniques, we successfully tracked the distribution and biotransformation dynamics of CdSe quantum dots (QDs) during their transport from Shewanella onedensis to Caenorchabditis elegans in predation. Fluorescence microscopy and Raman mapping showed that the ingested QDs by C. elegans were located at the gut lumen and subcutaneous tissue, and were partially excreted from the nematode body over time. Micro-X-ray fluorescence (µ-XRF) spectroscopy and Se K-edge X-ray absorption fine structure (XAFS) results further revealed the changed distribution of Se element over time, and a shift in the major Se species from CdSe to Se0 and Na2SeO3IV. This work demonstrates the utility of advanced spectral techniques for characterizing QDs in vivo, and may facilitate a better understanding on the environmental transformation and fates of ENMs.