Visualization of the cellular uptake of nanoparticles

The effect of nanoparticle charge and conjugation to the cell penetrating peptide Tat on the uptake of nanoparticles into MRC-5 fibroblasts was investigated using a range of advanced imaging techniques including atomic force microscopy (AFM), scanning ion conductance microscopy (SICM) and fluorescence microscopy. New technologies are required to investigate the uptake of nanoparticles since although many studies have examined their destination within cells, little work has been done looking at the interaction between the nanoparticles and cell which also plays an important role. Polyacrylamide nanoparticles showed a clear correlation between increased positive charge and cellular uptake. These results obtained using fluorescence microscopy correlated well with those observed using AFM. Nanoparticles with low levels of positive charge caused minor effects on bilayer structure such as fusion of holes in the bilayer, whilst negatively charged nanoparticles had no effect on the bilayer. Polyacrylamide nanoparticles conjugated to the cell penetrating peptide Tat displayed greater cell uptake and increased effects on the bilayer depth and coverage than the similarly charged nanoparticles alone. This indicated that the peptide leads to enhanced uptake by additional mechanisms other than just the presence of a positive charge. In contrast, silica nanoparticles with high levels of positive and negative charge entered cells to a similar extent. However, when the interaction with the cell membrane was imaged using Scanning Surface Confocal Microscopy (SSCM), there were differences. Nanoparticles possessing a negative charge were often found to be associated with extensions of the membrane. Positively charged particles were also found associated with membrane extensions in some cases but were also observed isolated on the membrane. The results highlight the importance of using multiple imaging techniques to investigate cellular interaction and uptake in order to provide a complete picture of all the processes involved