Light-activated coating kills bacteria

Scientists have developed a new coating that kills bacteria under ambient light conditions. Photo courtesy of University College London

March 5 (UPI) -- Scientists have developed a new light-activated coating that kills bacteria. The coating could be applied to phone screens and keyboards to curb the spread of harmful bacteria.

More importantly, the coating could be used on medical equipment like catheters and breathing tubes, the main sources of of healthcare-associated infections. The most common healthcare-associated infections are caused by Clostridioides difficile, methicillin-resistant Staphylococcus aureus, or MRSA, and E. coli.

In lab tests, the new antimicrobial coating successfully killed bacteria when exposed to low intensity, ambient light, the kind of light commonly found in hospital wards. The coating's antibacterial properties were activated by light levels as low as 300 Lux. Most light-activated antimicrobial coatings require lights as bright as 3,000 Lux.

Researchers created the coating by embedding chemically modified gold in a polymer with crystal violet, a medical dye boasting antibacterial and antifungal properties. The dye is also antihelmintic, which means it is hostile to small parasites.

Scientists described the novel coating Thursday in the journal Nature Communications.

"Dyes such as crystal violet are promising candidates for killing bacteria and keeping surfaces sterile as they are widely used to disinfect wounds," first author Gi Byoung Hwang, a chemist at University College London, said in a news release. "When exposed to bright light, they create reactive oxygen species, which in turn kill bacteria by damaging their protective membranes and DNA. This is amplified when they are paired with metals such as silver, gold and zinc oxide."

During the initial test phases, scientists found a control coating of crystal violet in a polymer was not enough to kill either S. aureus or E. coli bacteria under ambient light. However, the new bactericidal coating slowed the proliferation of each bacteria. Tests showed the coating took longer to curb E. coli growth.

"E. coli was more resistant to the bactericidal coating than S. aureus as it took longer to achieve a significant reduction in the number of viable bacteria on the surface," said Elaine Allan, UCL researcher and study co-author. "This is presumably because E. coli has a cell wall with a double membrane structure, whereas S. aureus only has a single membrane barrier."

The tests results showed the coating's production of hydrogen peroxide was responsible for killing the bacteria.

"The gold clusters in our coating are key to generating the hydrogen peroxide, through the action of light and humidity," said senior study author Asterios Gavriilidis, professor of chemical engineering at UCL. "Given the clusters contain only 25 atoms of gold, very little of this precious metal is required compared to similar coatings, making our coating attractive for wider use."

Researchers suggest the new coating could be incorporated into a variety of healthcare environments in the near future.

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