University of Toronto: With the flip of a switch, UV-LED lights could be used to kill coronaviruses and other germs: U of T study

Lighting used in offices and public spaces could potentially be used to destroy coronaviruses and HIV.

In a study published this week in Virology Journal, researchers at the University of Toronto killed both viruses using UV-LED lights, which can alternate between white light and decontaminating ultraviolet (UV) light.

Moreover, the UV-LED lights could also be used in many standard lighting fixtures with a cheap retrofit, giving them a “unique appeal” for public spaces, says the study’s senior author Christina Guzzo.

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Christina Guzzo
“We’re at a critical time where we need to use every single possible stop to get us out of this pandemic,” says Guzzo, an assistant professor in the department of biological sciences at U of T Scarborough. “Every mitigation strategy that can be easily implemented should be used.”

UV lights kill viruses through radiation. Working with PhD students Arvin T. Persaud and Jonathan Burnie, Guzzo first tested the lights on bacterial spores that are notorious for their resistance to this radiation (known as Bacillus pumilus spores).

“If you’re able to kill these spores, then you can reasonably say you should be able to kill most other viruses that you would commonly encounter in the environment,” says Guzzo, principal investigator at the Guzzo Lab.

Within 20 seconds of UV exposure, the spores’ growth dropped by 99 per cent.

The researchers then created droplets containing coronaviruses or HIV to mimic the typical ways people encounter viruses in public, such as from coughing, sneezing and bleeding. The droplets were exposed to UV light and placed in a culture to see if any of the virus remained active. With just 30 seconds of exposure, the ability of the virus to infect dropped by 93 per cent.

Upon testing the viruses at different concentrations, the researchers found that samples with more viral particles were more resistant to the UV lights. But even with a viral load so high Guzzo calls it “the worst-case scenario,” infectivity still dropped by 88 per cent.

While the lights themselves aren’t harmless – UV radiation damages nucleic acid, and repeated, prolonged exposure is harmful – Guzzo says they could be easily employed when public spaces are empty – such as on vacated buses that have finished their routes or empty elevators travelling between floors. Escalator handrails, meanwhile, could be continuously disinfected by putting UV lights in the underground part of the track, cleaning it with each rotation, she adds.

Safe Antivirus Technologies, Inc., a Toronto-based start-up company that partnered with Guzzo for the study, is developing unique UV-LED lighting modules. With motion sensors, the lights automatically switch to UV light when a room is empty, then turn back to regular light with movement.

Though it wasn’t included in the study, Guzzo and her students compared UV light to two heavy-duty disinfectants used in lab research. They found the lights were similarly effective in their ability to deactivate viruses.

“I was really surprised that UV could perform on the same level of those commonly used lab chemicals, which we regard as the gold standard,” Guzzo says. “That made me think, ‘Oh, my gosh, this is a legitimate tool that’s really underutilized.’”

While the lights left a small percentage of the virus viable, Guzzo says they could contribute to the “Swiss cheese model” of defence against COVID-19: Every strategy to fight the spread has its holes, but every layer is another chance to stop straggling virus particles.

Repeated exposure to UV light is key to catching those missed particles – and, fortunately, it’s as easy as flipping a switch. Guzzo notes that UV-LEDs are cheap and could be easy to retrofit in existing light fixtures, and that the bulbs are long-lasting and simple to maintain.

“You could disinfect in a way that wouldn’t be infringing on people’s enjoyment of that everyday ‘normal’ life that they long for,” Guzzo says.

The lights also benefit from automation. A standardized, germicidal dose of light can be delivered each time, while the process of wiping down spaces with disinfectants leaves room for human error. Plus, chemicals and waste from these disinfectants also end up in watersheds and landfills as hands are washed and wipes thrown away.

Guzzo says the research, funded by a Natural Sciences and Engineering Research Council (NSERC) Alliance COVID-19 Grant, suggests UV-LEDs are a tool that could be used to help prevent a future pandemic.

“Worldwide events like the COVID-19 pandemic, as terrible as they are, hopefully can still be learned from,” Guzzo says. “One thing we learned is that this is an underutilized tool we should think more about implementing.”

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