Reprint: Physics World, June 2020
Author: Jon Cartwright
Imagine a world where people travel as they wish. They shake hands when they make new
acquaintances, embrace when they greet close friends and elderly relatives. They do not bother to
laboriously disinfect their work surfaces, or wash their hands once they have dealt with the post. They go
shopping as they please and find no shortage of provisions. They work in offices, laboratories, shops,
restaurants and building sites. They conduct meetings in person, and think nothing of it when they jet off
to their favourite holiday destination.
They do all this because a COVID-19 vaccine has been developed,tunable and longer-lasting, among other benefits. The potential of far-ultraviolet light for the next pandemic – Physics World
rolled out and administered to the entire populace, making all the chaos of 2020 a distant memory.
Everything is back to normal.
This is the ending to the coronavirus pandemic we are all hoping for, and, give or take some of the
details, there is no reason why it is not possible. But even in this optimistic scenario, there is a deep fear
among scientists and policy makers: what happens next time? For if there is one lesson that COVID-19
has taught us, it is that our modern lifestyles are fatally ill-suited to the emergence of novel viruses –
and novel viruses there will always be. Any drugs and vaccines we develop for COVID-19 will be
ineffectual against the next viral pandemic, which may well consist of a different family of virus
altogether. Indeed, unless anything in our approach to pandemics changes, the next one will entail
another psychologically and economically crippling lockdown while scientists find a cure – however long
Yet according to one scientist, there is something we can do differently next time. Charlie Ironside of
Curtin University in Perth, Australia, is not a virologist or an epidemiologist but a physicist – one who has
spent 30 years specializing in semiconductor optoelectronics. His solution: far-ultraviolet light-emitting
diodes (far-UV LEDs).
But not all wavelengths of UVC are as damaging as others, as a group of researchers led by physicist
David Brenner at Columbia University in New York, US, showed in 2017. Their research relied on an
excimer lamp – a type of light tube containing molecules, or excimers, that can briefly exist in an excited
electronic state before returning to their ground state, and in doing so emit UV radiation at various
wavelengths in the UVC band depending on the molecules used. On exposing mice to 222 nm, far-UVC
light from a krypton-chlorine excimer lamp, Brenner and colleagues found no evidence of skin damage,
even though they found that the same light was effective at killing the superbug MRSA (Radiat. Res.
The result was corroborated a year later by Kouji Narita at the Hirosaki University Graduate School of
Medicine in Japan and colleagues. This team also confirmed that the 254 nm-wavelength emission of a
conventional germicidal lamp did induce sunburn-like skin damage (PLOS One 13 e0201259). That
same year, Brenner and colleagues found that 222 nm light is able to destroy airborne viruses as well.
In their test, with an exposure of just 2 mJ/cm , the far-UVC radiation safely inactivated more than 95%
of airborne H1N1 influenza, the virus behind the 2009 swine flu pandemic (Sci. Rep. 8 2752). There is
even evidence that far-UVC light is safe for the eyes: last year, Sachiko Kaidzu of Shimane University in
Izumo, Japan, found no damage to the corneas of rats exposed to 222 nm electromagnetic radiation
(Free Radic. Res. 53 611).
The reason for the lack of skin damage from far-UVC light, according to Brenner, is simply down to the
range of absorption in biological materials (see box above). Being a shorter wavelength than other UVC
light, far-UVC photons are barely able to penetrate the skin’s outermost layer of dead cells, which is
often tens of microns thick. On the other hand, it can still easily penetrate bacteria and viruses, which
are usually less than 1 μm thick. As Brenner said in a TED talk in late 2017, “I’m thrilled that we’ve now
got a completely new weapon against superbugs” – and, he later noted, viruses.
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