Tailor the antibacterial efficiency of copper alloys by oxidation: when to and when not to

Abstract

Copper and its relevant species, such as oxides and many alloys, have been recognised as potential antibacterial surfaces. Despite the relatively low antibacterial efficacy of cuprous oxide (Cu2O) compared to pure copper, it is still worth consideration in some scenarios. Taking copper-nickel co-sputtered thin films with two copper contents (55 and 92 at.%) as examples, this work investigated the potential of oxidation in altering the antibacterial behaviour of copper alloy surfaces. By heat treatment at 200–250 °C for 20–24 h, a layer mainly composed of Cu2O was successfully fabricated on the top of the Cu-Ni alloys. Antibacterial efficiency against Escherichia coli in 1 h was obtained by the droplet method and further compared. The coupons with 92 at.% copper became less effective after oxidation: the reduction rate declines from 97.0 to 74.3%; whereas the coupons with 55 at.% copper showed a large increase after oxidation, rising from 15.0 to 66.8%. The experiments described herein reveal a promising concept of oxidation in enhancing the less effective copper alloy surfaces for antibacterial applications. Graphical abstract: [Figure not available: see fulltext.]