Quantitative assessment of the comparative nanoparticle-uptake efficiency of a range of cell lines

Interest continues to grow in the possibility of understanding the mechanism(s) of nanoparticle-cell interactions. At present there is little knowledge, and essentially no understanding, of the relevant length and time scales for nanoparticle-intracellular entry, and localization within cells, and the cell-specificity of nanoparticle uptake and localisation. We have investigated here the effect of particle size on the in vitro intracellular uptake of model fluorescent carboxyl-modified polystyrene nanoparticles in various cell lines commonly used for uptake studies. A range of micro- and nanoparticles of defined sizes (40 nm to 2 μm)were incubated with a series of cell types, including HeLa and A549 epithelial cells, 1321N1 astrocytes, HCMEC D3 endothelial cells and murine RAW 264.7 macrophages. Techniques such as confocal microscopy and flow cytometry were used to study particle uptake and sub-cellular localisation, making significant efforts to ensure reproducibility in a semi-quantitative approach. The results indicated that internalization of (nano)particles is highly size dependent for all cell lines studied and that the kinetics of uptake for the same nanoparticle varies in the different cell types. Interestingly, even cells non specialized for phagocytosis were able to internalize the larger nanoparticles. Intracellular uptake of all sizes of (nano)particles was observed to be the highest in RAW 264.7 cells (a specialized phagocytic cell line) and the lowest in the HeLa cells. Results suggests that (nano)particle uptake might not follow commonly defined size limits for uptake processes and highlights the variability of uptake kinetics for the same material in different cell types. These conclusions have important implications for the assessment of the safety of nanomaterials and potential biomedical applications of nanoparticles.