Accelerated Escherichia coli inactivation in the dark on uniform copper flexible surfaces

The bacterial inactivation of Escherichia coli on Cu/CuO-polyester surfaces prepared by direct current magnetron sputtering was investigated in the dark and under actinic light (360 nm≤ λ ≤ 720 nm; 4.1 mW/cm2) as used commonly in hospital facilities. In the dark, complete bacterial inactivation (6log10 reduction) was observed within 150 min and under actinic light within 45 min. Sputtered samples led to nanoparticulate uniform Cu/CuO films ∼70 nm thick. The deposition rate used was 2.2×1015 atoms/cm2 s as determined by profilometry. X-ray fluorescence was used to determine the sample Cu-content and transmission electron microscopy determined Cu-particles ∼20 ± 5 nm in size. The film optical absorption was observed to increase with Cu-content of the sample by diffuse reflection spectroscopy. The bacterial inactivation involved redox processes between Cu/CuO-polyester and the bacteria as observed by x-ray photoelectron spectroscopy. During sample recycling, the amount of Cu-release was determined by inductively coupled plasma-mass spectroscopy. The values required for E. coli inactivation were below the cytotoxicity level threshold allowed for mammalian cells. The E. coli inactivation by Cu/CuO-polyester seems to involve an oligodynamic effect since bacterial inactivation was achieved at very low Cu-concentrations.