The dark-field images for 45-nm-AuNPs and cells. (a) The dark-field CCD images for 45-nm-AuNPs and a CL1-0 cell at different interaction time. The focus plane was fixed near the glass substrate, i.e. Δz = 0. The scale bar is 10 μm. (b) An enlarged image of Figure 5(a) for 120 minutes interaction time. The AuNPs showed yellow colors. When they were uptaken by the cell, the AuNPs became orange with blue surroundings. The picture demonstrated the movement and uptake of AuNPs for 45 nm and 70 nm AuNPs. Many 45-nm AuNPs are moved and then uptaken by cells, while many 75-nm-AuNPs only moved to the apical surface of the cells.