The objectives of this study were to determine the absorption of single-wall carbon nanotubes (SWCNTs) across the gut epithelial cells in Daphnia magna and to determine if absorption was influenced by their surface functionalization. This project utilized several microscopic techniques including micro-Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and analytical TEM with electron energy loss spectroscopy (EELS) and selective area diffraction (SAD). Four groups of differently functionalized SWCNTs were used: hydroxylated (OH-SWCNTs), silica dioxide (SiO2-SWCNTs), poly aminobenzenesulfonic acid (PABS-SWCNTs) and polyethylene glycol (PEG-SWCNTs). Raman spectroscopy was able to detect OH-SWCNTs suspended with natural organic matter (NOM) within the gut. However, the technique lacks the spatial resolution that is needed to identify lower concentrations of SWCNTs that may be absorbing into body tissues. Therefore, D. magna exposed to OH-SWCNT, SiO2-SWCNT, PABS-SWCNT, and PEG-SWCNT were sectioned and imaged with TEM. Although several areas of tissues were found to contain features that initially suggested absorption of SWCNTs, subsequent analysis with additional TEM techniques (HRTEM, EDS, and SAD) indicated that these were in fact due to staining or other organic structures. This is not meant to definitively indicate that no absorption occurred, but rather that we were unable to detect as much using analytical TEM. Conclusive detection of SWCNTs in the organism tissue proved to be substantially more challenging than anticipated.
Pub Type: Journals