A research team from the University of Canterbury (UC) (Christchurch, New Zealand) is developing a germ-free surface coating that, once it becomes commercially viable, may be applied to high-traffic areas. This antimicrobial coating would be particularly useful in reducing the spread of infections in hospitals and other such environments.
The genesis of this project occurred over a decade ago when Susan Krumdieck, currently a professor in UC’s mechanical and materials engineering department, worked with titanium(IV) oxide (TiO2). A well-known ceramic compound, TiO2 is typically bright white or transparent but, to Krumdieck’s surprise, “one day the coating came out all black.” Krumdieck set the TiO2 aside but when undergraduate students later tested it, the element had changed. “It was so photocatalytically active without any ultraviolet (UV) radiation that we knew we had discovered something new,” Krumdieck said.
Because of its ability to absorb radiation, TiO2 is commonly used in sunscreens. This radiation absorption process creates energy that is expressed in oxygen ions, which are deadly to bacteria. This makes TiO2 an ideal coating for surfaces, such as door handles, in environments that prioritize sterility. With that said, two unresolved questions prevent it from being used for that purpose: how can the coating be fixed onto surfaces such as door handles and how can it be activated without UV radiation?
To answer those questions, Krumdieck led an interdisciplinary team of 14 UC researchers that looked to the black TiO2 coating. One of the research collaborators, Tim Kimmett at Callaghan Innovation, helped deduce that the coating’s unusual nanostructures and black color made it a new material. Krumdieck further examined samples of the coating months later while a visiting research fellow at Université Grenoble Alpes (Grenoble, France). A team of French researchers analyzed the coating and discovered that the crystals were nanostructured in such a way that enabled visible light antimicrobial activity.
Krumdieck took this insight with her back to UC and asked her colleague Jack Heinemann, a UC professor specializing in microbiology, to assist her in setting up a testing system. “Sure enough, the bacteria did not stand a chance—even after a short time in visible light,” Krumdieck said.
The fact that radiation is not needed to energize the black TiO2 coating, and with an altered nanostructure that enables it to be a fixed coating, Krumdieck’s team are now proceeding with exploring the coating’s commercial applications. Having successfully applied it to a door handle, the UC researchers are working with other companies to design and upscale the coating for advanced manufacture. More information about the research that went into the TiO2 project can be seen in their report for the science magazine Nature.