Bactericidal activity of silver nanoparticles: An analytical approach based on single cell and single particle inductively coupled plasma mass spectrometry analysis to determine silver species involved

The bactericidal activity of silver nanoparticles is supported by a large number of studies, but their action mechanisms are still a controversial issue due to the role of the silver (I) released from the nanoparticles. In this study, direct analytical methods for detection and identification of dissolved and nanoparticulate silver based on single cell and single particle inductively coupled plasma mass spectrometry (ICP-MS) and hydrodynamic chromatography ICP-MS, in combination with alkaline digestions, have been used. Detection of silver species in Escherichia coli bacteria exposed to silver allowed to confirm the different bactericidal activity associated with silver nanoparticles of different sizes. In the case of 10 nm silver nanoparticles, a combined ion-particle action would be responsible for bactericidal effect, since ionic silver was not detected in the culture medium and both dissolved and particulate silver were detected in the exposed bacteria. On the other hand, bacteria did not internalize 60 nm silver nanoparticles and their bactericidal activity was related to the ionic silver released in the culture medium.