The physicochemical characterization of the Cu nanoparticle surface, and of its evolution on atmospheric exposure: Application to antimicrobial bandages for wound dressings

We have used X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, transmission electron microscopy and reconstructed electron diffraction patterns, to study the contamination of the Cu nanoparticle surface on atmospheric exposure, as would occur on using such nanoparticles as antimicrobials deposited onto bandages intended for use as wound dressings. Our study suggests that the surface contaminant initially formed by residual gases in vacuum is Cu2CO3. On atmospheric exposure, this is oxidized to CuCO3, combined with Cu(OH)2, as found in azurite and malachite; pure CuO is not found in nature. On subsequent exposure to high energy irradiation, which might occur in the bandage packaging process, the azurite/malachite contaminant breaks down, forming CuO, which is reduced by reaction with carbon, forming Cu0, before ultimately re-oxidizing to reform the surface contaminants. We discuss the implications of these results on possible mechanisms of the antimicrobial action of such nanoparticles when deposited onto bandages.