Antibacterial properties of novel transparent copper films: a potential new tool to reduce healthcare-associated infections in hospitals and healthcare facilities

Abstract

Background: Healthcare-associated infections (HAIs) are serious public health issues, and environmental surfaces contaminated with microorganisms have been reported to play an important role in their occurrence. We focused on copper, which is known to have excellent antimicrobial activity, as a measure to prevent contamination of environmental surfaces. In hospital environments, copper has been used on handrails and doorknobs. However, its use has been limited because of its opaque nature. Therefore, we developed a thin, highly transparent copper film via the sputtering method. This study examines the antimicrobial activity of this transparent film to expand the potential applications of copper to commonly used surfaces in healthcare settings.

Methods: Polyethylene terephthalate film was coated with a copper layer of four different thicknesses via the sputtering method. The antimicrobial activity of the copper film was evaluated according to the ISO22196:2011 standards. The antimicrobial activity and the change in the viable bacteria count with contact time between the test bacteria and the copper film surface were evaluated.

Results: For all copper layer thicknesses, the bacterial count decreased exponentially after contact with the copper film. For Escherichia coli, the count decreased 100-fold after 10 min, and no viable bacteria were observed within 30 min. For Staphylococcus aureus, the count decreased 100-fold after 20 min, and no viable bacteria were observed within 50 min. In these two bacterial species, the antibacterial activity did not differ according to the thickness of the copper layer.

Conclusion: All copper films showed sufficient antimicrobial activity against Escherichia coli and Staphylococcus aureus regardless of the copper layer thickness. The thinnest 5 nm copper film with high transparency was considered most useful for medical applications because of its visibility. Further study is needed to determine whether this transparent copper film reduces microbial contamination on environmental surfaces and contributes to reducing HAIs in hospitals and healthcare facilities.

Keywords: Escherichia coli; Staphylococcus aureus; Antimicrobial activity; Bacterial count; Contact time; Copper film; Environmental surface; Transparency.

Fig. 1

Photographs of the films with copper coatings of different thicknesses Films were coated with copper layers of different thicknesses. The samples were photographed using a digital camera (LUMIX DMC-FT25, Panasonic)

Fig. 2

Comparison of text legibility through films with copper coatings of different thicknesses The photograph shows how the thickness of copper influences the transparency and visibility of printed letters on a white sheet of paper. The samples were photographed under identical lighting conditions using an automatic colony counter (PSF-2100, SHASHIN KAGAKU)

Fig. 3

Effects of contact time and copper coating thickness on bacterial count Colony counts of Escherichia coli (A) and Staphylococcus aureus (B) on a transparent copper film over contact time (pink line; 0 nm copper coating film as a control, light blue line; 5 nm copper coating film, dark blue line; 10 nm copper coating film, light green line; 20 nm copper coating film, dark green line; 30 nm copper coating film). The plots show the mean values, and the error bars represent the standard deviation across three replicates CFU, colony forming unit