Every cell has a silver lining! The toxicity of Ag nanoparticles is investigated using a panel of recombinant bioluminescent bacteria. The presence of the nanoparticles leads to the production of a superoxide radical (see figure). Furthermore, the Ag nanoparticles damage the cellular membranes, causing a disruption in the ion efflux system. Thus, the cells cannot effectively extrude the Ag ions and, hence, Ag nanoparticles cause more damage than do Ag ions.