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Among the many problems we have had with the spread of COVID-19 is the ability of the coronavirus to survive on surfaces for hours on end. While we can effectively clean hard materials or sterilize them with alcohol, what about more delicate surfaces like cardboard?
Even in the atmosphere, SARS-CoV-2 can survive for up to a few hours; on cardboard can last up to 24 hours and viable particles were detected on the plastic for up to three days after it was contaminated.
Scientists from many disciplines are using their vast talents to tackle the pandemic. Now, a team led by engineer Zhitong Chen of the University of California at Los Angeles may have found a solution. They just showed that cold plasma has the ability to destroy the virus on a wide range of surfaces without damaging the material.
“Everything we use comes from the air,” explains aerospace engineer Richard Wirz. “Air and electricity: it’s a very healthy treatment with no side effects”.
Plasma, the least known of the four main states of matter (the other three are solid, liquid, and gaseous), occurs naturally in our upper atmosphere. It forms when electrons separate from their atoms (making the atoms positively charged) and together create a soup of charged particles that are unstable and therefore more reactive than their equivalent gaseous state.
Cold plasma has already been shown to work against drug-resistant bacteria. It interferes with their surface structure and DNA without damaging human tissues. It also works against cancer cells.
Chen, Wirz and colleagues designed and 3D printed an atmospheric plasma jet device powered by argon gas, an inert and stable element that is one of the most abundant gases in our air. The device sends electrons at speed through the gas, ripping off the gas atoms of the outer electrons when they collide; it only requires 12W of continuous power to work.
The team directed a stream of reactive particles at near room temperature onto contaminated surfaces, exposing them to an electric current, charged atoms and molecules (ions), and UV radiation.
They tested the plasma effect on six surfaces, including cardboard, football skin, plastic, and metal, and found that on each of them most of the virus particles were inactivated after just 30 seconds. Three minutes of contact with the plasma destroyed the entire virus.
The team believes that it is the reactive oxygen and nitrogen ions formed when plasma interacts with air that are destroying the viral particles; when they tested a helium-fed plasma, which produces fewer of these kinds of atoms, it wasn’t effective even after five minutes of application.
They explain that when charged particles collect on the virion’s surface, they can damage its envelope through electrostatic forces that lead to its rupture. Ions can also break structurally important bonds such as those between two carbon atoms, carbon and oxygen and carbon and nitrogen atoms.
Experiments on the effects of plasma on bacteria and viruses have revealed that damage to the virus outer envelope can include proteins that are important for binding to host cells.
“These results also suggest that cold plasma should be studied for the inactivation of aerosol-borne SARS-CoV-2,” Wirz and colleagues wrote in their paper.
Last year another team created a plasma filter that can sterilize the air from 99% of viruses. In their device, as the air moves through the slits in a bed of borosilicate glass beads, the unstable atoms that form the plasma are oxidized. This damages the viral particles, leaving them with a greatly reduced ability to infect us.
Of course, there is still a way to go from proof of concept to a device we can all use. But Wirz and the team are now working on creating such a device.
“This is just the beginning,” Wirz said. “We are very confident and have very high expectations for plasma in future work.”
This research was published in Fluid physics.
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