Copper-based Surface Coatings and Antimicrobial Properties Dependent on Oxidation States

Copper is cost-effective and abundantly available as a biocidal coating agent for a wide range of material surfaces. Natural oxidation does not compromise the efficacy of copper, allowing it to maintain antimicrobial activity under prolonged exposure conditions. Furthermore, copper compounds exhibit a broad spectrum of antimicrobial activity against pathogenic yeast, both enveloped and non-enveloped types of viruses, as well as gram-negative and gram-positive bacteria. Contact killing of copper-coated surfaces causes the denaturation of proteins and damage to the cell membrane, leading to the release of essential components such as nucleotides and cytoplasm. Additionally, redox-active copper generates reactive oxygen species (ROS), which cause permanent cell damage through enzyme deactivation and DNA destruction. Owing to its robust stability, copper has been utilized in diverse forms, such as nanoparticles, ions, composites, and alloys, resulting in the creation of various coating methods. This mini-review describes representative coating processes involving copper ions and copper oxides on various material surfaces, highlighting the antibacterial and antiviral properties associated with different oxidation states of copper.