New Evidence for Ag-Sputtered Materials Leading to Bacterial Inactivation by Surface-Contact without the Release of Ag-ions: End of a Long Controversy?

The study provides new evidence for Ag-coated polyester (PES) mediating E. coli inactivation by way of genetically engineered E. coli (without porins, from now as porinless bacteria). This allows the quantification of the bactericidal kinetics induced by Ag-surface without the intervention of Ag-ions. Bacterial inactivation mediated by Ag-PES was seen to be complete within 60 min. The samples were prepared by high-power impulse magnetron sputtering (HiPIMS) at different sputter powers. In anaerobic media, this process required 120 min. The amounts of ions (Ar+, Ag+ and Ag2+) generated during the deposition by direct current magnetron sputtering (DCMS) and HiPIMS were determined by mass-spectrometry. The thickness of the Ag-films sputtered on PES by DCMS (0.28 A) during 100s was found to be 340 nm. Thicknesses of 250, 230 and 200 nm were found when sputtering with HiPIMS tuned at 8A, 17A and 30A respectively. By scanning transmission electron microscopy (STEM-HAADF), the atomic distribution of Ag and oxygen was detected. By X-ray photoelectron spectroscopy (XPS), a shift in the Ag-oxidation state was observed within the bacterial inactivation period. This reveals redox catalysis within the time required for the total bacterial inactivation due to the interaction between the bacterial suspension and Ag-PES. Surface properties of the Ag-coated PES samples were additionally investigated by X-ray diffraction (XRD). The formation of Ag-plasmon was detected by diffuse reflectance spectroscopy (DRS) and was a function of the applied sputtering energy. The indoor sunlight irradiation dose required to induce an accelerated bacterial inactivation was found to be 5-10 mW/cm2.