Visualizing the uptake of C60 to the cytoplasm and nucleus of human monocyte-derived macrophage cells using energy-filtered transmission electron microscopy and electron tomography.

Concerns have been raised over the release of C60 nanoparticles into the environment and the potential risk to human health. To address these concerns it is essential to understand the pathways by which nanoparticles enter the cell, where they migrate to, and to establish whether the particles are transformed or modified within the cell. Imaging the subcellular distribution of carbon-based nanoparticles is particularly challenging. It is difficult to achieve high spatial resolution with sufficient image contrast to enable the nanoparticles to be identified within the cell. We have exposed human monocyte-derived macrophages (HMMs) to C60 and used energy filtered transmission electron microscopy (EFTEM) to image the distribution of C60 aggregates within intracellular compartments. We demonstrate that images recorded using low-loss electrons provide a significant improvement in contrast between the cellular material and the C60 allowing a clear differentiation between C60 and unstained cellular compartments and also between ordered and disordered forms of aggregated C60. We confirm that C60 is taken up by HMMs in vitro and is sequestered at several sites within the cell. These sites include the cytoplasm, lysosomes, and most significantly the cell nuclei.