Transmission electron microscopy for elucidating the impact of silver-based treatments (ionic silver versus nanosilver-containing coating) on the model yeast Saccharomyces cerevisiae

After exposure to ionic silver or nanosilver-containing plasma coating, the same visual aspect of scanning transmission electron microscopy (STEM) images was observed for the model yeast Saccharomyces cerevisiae. The main common feature was the presence of electron-dense nodules all over the cell. However, high resolution TEM (HRTEM), STEM, energy dispersive x-ray microanalysis spectroscopy (EDS) and electron microdiffraction revealed some striking differences. Regarding ionic silver exposure, the formation of electron-dense nodules was related to the Ag (broken vertical bar) reactivity towards sulfur-containing compounds to form clusters with Ag2S-like structures, together with the production of a few silver nanocrystals, mainly at the cell wall periphery. For nanosilver-based treatment, some sulfur-containing silver clusters preferentially located at the cell wall periphery were detected, together with nodules composed of silver, sulfur and phosphorus all over the cell. In both silver-based treatments, nitrogen and silver signals overlapped, confirming the affinity of silver entities for proteinaceous compounds. Moreover, in the case of nanosilver, interactions of silver with phosphorus-containing subcellular structures were indicated.