Bacteria-induced changes in the ultrafast plasmonic response of silver nanostructured surfaces*

The antimicrobial properties of silver have been known for millenia, finding use in coinage, cutlery, medical device coatings, and textiles. The consensus regarding the origin of this mechanism is that bacterial metabolism is disrupted by uptake of silver ions following oxidative dissolution at the bacteria-silver interface. The manifestation of this interaction on the plasmonic response of silver nanoparticles is investigated here. Changes in the nanoparticle crystallinity, size, and shape are observed after interaction with E.coli via transient absorption spectroscopy. Bacterial exposure leads to a decrease in the electron-phonon coupling time, an increase in the lattice-environment coupling time, and rapid damping of coherent oscillations. This bacterial action was studied using E.coli, known to be susceptible to silver ion uptake, and was enhanced with a membrane permeability-increasing agent. The changes in the plasmonic response are explained by an increase in the free electron density and amorphization of the silver nanoparticles, as well as modification of the silver nanocrystal film thickness.