Apr 19, 2011
New insight into the biocide behaviour of nanosilver
Silver ions and nanosilver-containing coatings are well known for their biocide effects. After exposure to ionic silver or to a nanosilver-containing plasma coating, cells observed by scanning transmission electron microscopy (STEM) show the same visual aspect, namely, the presence of electron-dense nodules all over the cell. These observations could indicate that the interaction of silver with the cells is similar in both cases, and probably, that the reactivity of silver ions should only dominate the physicochemical interactions with cells. In fact, a deeper analysis by energy dispersive spectroscopy (EDS) and microdiffraction of electron-dense nodules reveals that the Ag+ and nanosilver interactions with the cells seem to be dissimilar and lead to the formation of clusters with a different chemical and structural nature.
Reporting their results in the journal Nanotechnology, researchers in France have used sophisticated electron microscopy techniques to investigate the biochemical effects of silver stress on the model yeast S. cerevisiae (eukaryotic cell) induced by exposure to a solution of silver nitrate or a nanosilver-containing organosilicon thin film.
The team used a large set of diagnostic methods based on transmission electron microscopy to investigate the impact of silver on intra- and extra-cellular structure and on biochemical components.
A chemical and structural analysis performed at the nanoscale (HRTEM, STEM, EDS) showed a clear differentiation between the observed electron-dense nodules. The silver nitrate solution induced the formation of silver nanocrystals and silver sulphur clusters whereas nanosilver-containing coating favoured the formation of clusters containing silver, phosphorus and sulphur. Moreover, an elemental mapmaking of each kind of treated cell indicated no identical behaviour of subcellular structure but underlined the key role of proteinaceous coumpounds in silver mass transfer.
The origin of such interactions should be explored in more detail in future work by coupling biochemical and physiological approaches.
The team's results provide new insight into the variety of silver effects (Ag+ and nanosilver) on microorganisms from a physicochemical point of view. Besides, this work emphasizes the ability of sophisticated electron microscopy techniques to perform structural and chemical analysis of cells at micro- and nanoscales.
Further details can be found in the journal Nanotechnology.
About the author
This study was performed by research teams from Université de Toulouse, France, based in two different laboratories (LAPLACE-UPS and LISPB-INSA). The teams were involved in a collaborative French research project (Research National Agency -ANR-07-BLAN-0196-01), which was focused on the biocide effect of a nanosilver-containing coating. Dr Bernard Despax is a senior researcher in plasma processes and the characterization of nanocomposite thin film materials. He performed and analyzed the electron microscopy results with Lucien Datas (an engineer from CIRIMAT laboratory) who is in charge of electron microscopy techniques at Université Paul Sabatier (TEMSCAN). Dr Claire Saulou, a biologist, was at that time a PhD student and performed plasma deposition process guided by Dr Despax and produced biological materials and biocide tests guided by Dr Muriel Mercier-Bonin. Moreover Dr Saulou has already provided numerous results on this subject, which have been published in previous papers guided by Dr Muriel Mercier-Bonin and the LAPLACE team. Dr Mercier-Bonin is a specialist in the formation of biofilms at LISBP laboratory and has managed the global ANR project with Dr Patrice Raynaud who is a group leader (LAPLACE: Material Plasma Processing).