Copper is a well-known metal that has a wide range of applications in the biomedical field due to its antimicrobial action against different pathogens. The ability of CuO NPs to kill bacteria at the contact phase allows for the development of multiple products, from antimicrobial solutions used for surface and medical device disinfection to antimicrobial wound dressings, textiles and coatings. The effectiveness of these products relies on the physicochemical properties of CuO NPs, especially their size and surface-area-to-volume ratio, as well as the synthesis method that affects the stability and toxicity of the copper ions they generate.
Among these properties, the luminescence of CuO NPs is one of the most important biomedical applications, since it can be used to enhance detection and differentiation between healthy and diseased tissues. Luminescence of planar copper nanostructures is caused by the interband transition between the d-band and the sp-conduction bands, which results in the radiative recombination of electron-hole pairs. The luminescence peak of CuO NPs is 530 nm when capped with linoleic acid, but can be enhanced to 350 nm through the absorption of UV radiation.
However, the toxicity of CuO NPs depends on the way they interact with the living organism, which is a complex process involving chemical transformations and biological uptake, as well as environmental factors and bacterial metabolism [31]. Several hypotheses for the interaction of copper NPs with bacteria are proposed. For example, the NPs may adhere to the membrane, changing its permeability, interfere with DNA replication and ribosomal functions, denature protein and generate reactive oxygen species.