The influence of nanoscopically thin silver films on bacterial viability and attachment

The physico-chemical and bactericidal properties of thin silver films (3 nm and 150 nm) have been analysed. The silver films were fabricated using a magnetron sputtering thin film deposition system. X-ray photoelectron (XPS) and energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM) analyses were done. The concentration of silver ions released from these films was measured by inductively coupled plasma time of flight mass spectroscopy (ICP-TOF-MS). Silver ion concentrations of 0.9 ppb and 5.2 ppb were detected for the 3 nm and 150 nm films, respectively. The surface wettability of the films remained nearly identical for both film thicknesses, showing a static water contact angle of approximately 95°.The two silver film thicknesses exhibited statistically significant differences in surface topographic profiles on the nanoscopic scale, with Ra, Rq and Rmax values of 1.4 nm, 1.8 nm and 15.4 nm for the 3 nm film and 0.8 nm, 1.2 nm and 10.7 nm for the 150 nm film over a 5 µm × 5 µm scanning area. Confocal scanning laser microscopy (CSLM) and scanning electron microscopy (SEM) showed that the bactericidal activity of the 3 nm silver film was not significant, whereas the nanoscopically smoother 150 nm silver film exhibited greater bactericidal activity towards Pseudomonas aeruginosa ATCC 9027 cells and Staphylococcus aureus CIP 65.8 cells, obtaining up to 75% and 27% sterilisation effect, respectively