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Among the many problems we have encountered with the spread of COVID-19 is the ability of the coronavirus to survive on surfaces for hours. While we can effectively wipe down 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, it can last up to 24 hours, and viable particles have been detected on the plastic for up to three days after contamination.
Scientists from many disciplines are putting their vast talents to work in the fight against the pandemic. Now, a team led by engineer Zhitong Chen of the University of California Los Angeles may have found a solution. They have just demonstrated 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 being solid, liquid, and gas), occurs naturally in our upper atmosphere. It is formed when electrons separate from their atoms (making atoms positively charged), and together create a soup of charged particles that are unstable and therefore more reactive than in 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 harming human tissue. It even 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 fast electrons through the gas, stripping the gas atoms of outside electrons when they collide; it only requires 12W of continuous power to operate.
The team directed a near-room temperature flow of reactive particles onto contaminated surfaces, exposing them to electric current, charged atoms and molecules (ions), and UV radiation.
They tested the effect of plasma on six surfaces, including cardboard, football leather, plastic and metal, and found that on each one, most of the virus particles were inactivated after just 30 seconds. Three minutes of contact with the plasma destroyed the entire virus.
The team believe that it is the reactive ions of oxygen and nitrogen, formed when plasma interacts with air, that destroy virus particles; when they tested a plasma fed with helium, which produces less of these atom species, it was not effective even after five minutes of application.
They explain that when charged particles collect on the surface of the virion, they can damage its envelope by electrostatic forces leading 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 outer shell of the virus can include proteins important for binding to host cells.
“These results also suggest that cold plasma should be studied for inactivation of aerosolized SARS-CoV-2,” Wirz and colleagues wrote in their article.
Last year, another team created a plasma filter capable of sterilizing the air of 99% of viruses. In their device, as air moves through the interstices of a bed of borosilicate glass beads, it oxidizes the unstable atoms that form the plasma. This damages the viral particles, leaving them with a drastically reduced ability to infect us.
Of course, there’s still a way to go from proof of concept to a device we can all use. But Wirz and his team are now working on building such a device.
“This is just the start,” 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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