Acridine orange/propidium iodide viability testing of SK1 yeast on NSS. (a,c,e) Images of acridine orange-stained SK1 yeast cells, showing viable cells. (b,d,f) Images of propidium iodide-stained SK1 yeast cells showing all cells with compromised plasma membranes, i.e. dying or dead cells. (a,b) SK1 yeast on control surfaces (Au-coated glass). (c,d) SK1 yeast on Au-coated Brd II NSS, note the large number of cells dying or dead. (e,f) SK1 yeast on Au-coated DD NSS, note the high fraction of cells staining with propidium iodide.