Titanium dioxide nanoparticles but not zinc oxide nanoparticles induced autophagy. H4-LC3-GFP cells were treated with zinc oxide (20 μg/ml) or titanium dioxide nanoparticles (10 μg/ml) for 18 hrs. 0.5% DMSO was used as a negative control. Rapamycin (0.2 μM) was used as a postive control. The images were recorded using a high-throughput microscope CellWoRx with a 10× objective. This experiment was repeated 2 times.