First unambiguous evidence for distinct ionic and surface-contact effects during photocatalytic bacterial inactivation on Cu–Ag films: Kinetics, mechanism and energetics

Abstract

Highly uniform Cu–Ag polyurethane (PU) sputtered films inactivated Escherichia coli presenting normal cell wall porins but were shown to require longer times to inactivate genetically modified porinless Escherichia coli. The Cu–Ag–PU films were observed to inactivate E. coli ∼7 times faster compared to Cu-films and ∼15 times faster compared to Ag-films by themselves under low intensity actinic light irradiation. The galvanic contact between Ag and Cu induces atomic disorder in the film leading to corrosion and release of ppb amounts of Ag and Cu. This is suggested to induce the oligodynamic effect responsible for the bacterial inactivation on the Cu–Ag films. By ATR-FTIR spectroscopy, the structural changes in the E. coli (LPS) bilayer were monitored during bacterial inactivation for porin and porinless bacteria. The Ag2Cu2O4 composite was found by X-ray photoelectron spectroscopy (XPS) to be the predominant species in the Cu–Ag films leading to bacterial inactivation. A mechanism is suggested for the photo-induced interfacial charge transfer (IFCT) between both metal oxides.