Electronic origin of antimicrobial activity owing to surface effect.

Nanomaterials have displayed promising potential as antimicrobial materials. However, the antimicrobial mechanism owing to surface effects, where the emission of harmful substances such as metallic ions and reactive oxygen species is not required, is still poorly understood. It is important to figure out relationship between the physical properties and antimicrobial activity based on deep understanding of antimicrobial mechanism for their safe and effective applications. Here, we show that the work function is representative of the surface effect leading to antimicrobial activity, which originates from the electronic states of the surface. We investigated the antimicrobial activity and the work function of nanoporous Au-Pt and Au without the emission of Ag ion, and found that there was a positive correlation between them. In addition, we performed a first-principles calculation and molecular dynamics simulation to analyze the electronic states of the Au surface and the cell wall. These demonstrated that positive correlation was owing to peculiar electronic states at the Au surface, namely, the spilling out phenomenon of electrons. Our finding will contribute to advance the understanding of biological phenomena from a physical view.