Intriguingly, we found that the internalization profiles of Au and Fe were different between OECM1 and HT-29. In accordance with our previous research,17,18 the nanoparticles served as a package of Fe and Au. The ratio of internalized Au and Fe elements should be constant, on average, and if the cells absorb a large number of unchanged nanoparticles. Intriguingly, when plotting the molar ratio of Fe to Au at different time points (Figure 9), it becomes apparent that different ratios occur between the different cell lines.