a) TEM‐images demonstrating uptake of Ag and Au NPs in the mouse retina. The top row shows the respective NP structure, i.e., AgNP 20 nm (A), AgNP 80 nm (B), AuNP 20 nm (C), and AuNP 80 nm (D). (E)–(P) All four types of NPs were taken up by the cultured retina and found in all three retinal nuclear neuronal layers, i.e., the GCL, INL, and ONL. Both 20 and 80 nm sized NPs were found either as single NPs (e.g., E, M (upper arrowheads) or as clusters of NPs (e.g., E, I, M (lower arrowheads). The 20 nm sized Ag and Au NPs, respectively, were found in the nucleus (E, G, I, K, M, O), the nucleolus (I, K, O), the mitochondria (G), the cytosol (E, G, M) and in the extracellular space (M). In the majority of cells the largest fraction of the 20 nm sized NPs were located in the nucleus (I, K, O) compared to the fraction of NPs found in the other cell compartments. Notably, all NPs were found both in the eu‐chromatin (e.g., I, K, N) and heterochromatin (e.g., I, K, L, P, M). Ag and Au NPs, sized 80 nm, were detected in the nucleus, but to a lesser extent compared to the 20 nm NPs (F, J, L, N, P) and in the extracellular space (H, L, P). NPs, sized 80 nm, were not detected in the nucleolus and within mitochondria. GCL = ganglion cell layer, INL = the inner nuclear layer, ONL = the outer nuclear layer. Arrowheads show NPs that have been taken up by the retinal cells. Scale bars equal 0.2 mm for images (A–D); 1 mm for (E,F), (I,J), and (M,N); and 0.5 mm for (G,H), (K,L), and (O,P). b) Increased number of apoptotic cells in the mouse retina after exposure to 20 and 80 nm Ag and Au NPs. Graph shows numbers of TUNEL‐positive cells and results are presented as mean ±SD (n = 5–8 explants per group). *p < 0.05 compared to control, **p < 0.01 compared to control. Scale bars equal 100 mm. c) Oxidative stress. Graph shows numbers of AvidinD‐positive cells and results are presented as mean ±SD (n = 4 explants per group). *p < 0.05 compared to control. Scale bars equal 100 mm. Reproduced with permission.62 Copyright 2014, Public Library of Science.