Copper layers sputtered on PTFE: Effect of annealing on antibacterial performance. (September 2020) - Lacmanova, V.
Graphical abstract: Highlights: Cu layers were prepared by sputtering on PTFE and annealed afterward. The effect of annealing on surface and antibacterial properties was examined. Annealing produced island structure consisting of more Cu 2+ oxides. Annealing evoked a loss of metallic behaviour of Cu showing in absorption spectra. The most effective against bacteria were non-annealed Cu layers. Abstract: The mechanism of antibacterial effect of copper nanostructures is still not fully recognized. Therefore, the goal of our work lies in investigating the impact of Cu sputtering and post-deposition annealing on surface and antibacterial properties of Cu layers created on polytetrafluoroethylene (PTFE). Subsequent annealing revealed intensified oxidation and rearrangement in the surface of Cu layers. Non-annealed Cu layers on PTFE consisted of Cu° and a mixture of Cu 1+ and Cu 2+ oxides. These layers exhibited properties similarly to bulk Cu, which were represented by surface plasmon resonance (SPR) band in UV–vis spectra and a soar in electrical conductance. On the contrary, annealed Cu layers possessed these characteristics leaving high electrical resistance and no SPR band. Moreover, X-ray photoelectron spectroscopy results revealed that the annealed layers prevailed of Cu 2+ oxides and the annealing process led to the formation of an island crystalline structure, disruption of layer continuity and exposure of the PTFE surface. Although the annealing process was not followed by significant changes in surface roughness, the island-like structure was well defined in atomic force and scanning electron microscopy images. Antibacterial tests were evaluated against Staphylococcus epidermidis and Escherichia coli . Annealed samples showed less pronounced antibacterial effect while non-annealed Cu layers sputtered for 400 s demonstrated the highest antibacterial effect against both bacterial strains. Such nanostructured substrates are promising for flexible electronics and biomedical application (i.e. bacterial biofilm inhibition).