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A ‘mini cyclone’ helps detect coronavirus in the air

Scientists have created an air-sampling machine that takes just minutes to detect the virus that causes COVID-19. This 3-D illustration shows the proposed final design of that device. Joseph

Scientists have created an air-sampling machine that takes just minutes to detect the virus that causes COVID-19. This 3-D illustration shows the proposed final design of that device.

Joseph Puthussery/Washington Univ. in St. Louis

By Tina Hesman Saey

August 9, 2023 at 6:30 am

If you ever walk into a room and wonder if the virus that causes COVID-19 is hanging around, you’re not alone. Now there’s a device that could answer that question. Researchers have created an air-sucking machine able to quickly detect the coronavirus.

The machine is a little bigger than a toaster. In just five minutes, it can detect as few as seven to 35 particles of the SARS-CoV-2 virus per cubic meter (35 cubic feet) of air. That’s about the same sensitivity as nasal swab tests that rely on PCR, says Rajan Chakrabarty. He’s an aerosol scientist at Washington University in St. Louis, Mo.

His team described its innovation July 10 in Nature Communications.

One challenge the team faced was collecting enough air to concentrate the coronavirus particles. Earlier systems developed by others sucked in between two and eight liters (quarts) of air per minute. This sampler pulls in 1,000 liters each minute.

To trap the virus, Chakrabarty says, his team created “an artificial cyclone inside of the sampler.” Once inside, the air is mixed with liquid in a fast-paced swirl. This cyclonic action slings the slurry against the detector’s wall. Any viruses will now concentrate there.

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A HEPA filter attached to the device removes any airborne viruses not captured in the liquid. After five minutes of collection, the system pumps the virus-rich liquid to a biosensor.

That sensor has an electrode attached to a specialized immune-system protein made by llamas and their relatives. Known as a nanobody, it fights infections like human antibodies do. But this protein is smaller and somewhat tougher.

The nanobody grabs the spike protein on any passing coronavirus. Electricity flows from the electrode through the nanobody and spike protein. That causes a particular amino acid — a building block of the spike protein — to lose electrons. Their loss causes a change in voltage. And that signals that SARS-CoV-2 is present.

The Washington University team placed its device in the apartments of two volunteers. Each had a confirmed COVID-19 infection. This would allow the team to test how well the tool could detect the virus in real-world conditions.

And it detected “even the trace amounts of virus being shed by the patients,” Chakrabarty says. When placed in an empty, well-ventilated conference room, the device turned up no virus.

“They’ve demonstrated that it works,” says Linsey Marr. She’s an aerosol scientist at Virginia Tech in Blacksburg. This new system can “detect [the] virus at low levels that we would be concerned about in the air,” she says. As part of studying how germs spread, Marr’s team is also developing a virus detector.

Some challenges remain. For one, the new device is noisy — about as loud as a vacuum cleaner or a ringing phone. People might find that tolerable for a short run. But that’s too loud, Marr says, to run non-stop in a classroom or office.

The system is costly, too. Chakrabarty says the cost of building one in a research lab runs around $1,400 to $1,900.

Commercial versions may start out too pricey for home use, Marr says. But she thinks hospitals, airports and other public areas could benefit from them. It might be possible to link the devices into the air supply for systems that heat, cool and ventilate buildings. Those systems could then ramp up air flow and filtration when virus is detected.

Meanwhile, Chakrabarty is already thinking of next steps for his team’s device. He hopes to add llama nanobodies to detect other airborne viruses as well, such as the one that causes flu.

aerosol: (adj. aerosolized) A tiny solid or liquid particle suspended in air or as a gas. Aerosols can be natural, such as fog or gas from volcanic eruptions, or artificial, such as smoke from burning fossil fuels.

antibodies: Any of a large number of proteins that the body produces from B cells and releases into the blood supply as part of its immune response. The production of antibodies is triggered when the body encounters an antigen, some foreign material. Antibodies then lock onto antigens as a first step in disabling the germs or other foreign substances that were the source of those antigens.

commercial: An adjective for something that is ready for sale or already being sold. Commercial goods are those caught or produced for others, and not solely for personal consumption.

coronavirus: A family of viruses named for the crown-like spikes on their surface (corona means “crown” in Latin). Coronaviruses cause the common cold. The family also includes viruses that cause far more serious infections, including SARS and COVID-19.

COVID-19: A name given to the disease that erupted into a massive global pandemic in 2020. It first emerged in 2019 and is caused by a new coronavirus known as SARS-CoV-2. Symptoms can include pneumonia, trouble breathing, feeling too tired to walk more than a few steps, fever, headaches, low blood-oxygen levels, blood clots and brain “fog.”

cyclone: A strong, rotating vortex, usually made of wind. Natural examples include a tornado or hurricane.

electricity: A flow of charge, usually from the movement of negatively charged particles, called electrons.

electrode: A device that conducts electricity and is used to make contact with non-metal part of an electrical circuit, or that contacts something through which an electrical signal moves. (in electronics) Part of a semiconductor device (such as a transistor) that either releases or collects electrons or holes, or that can control their movement.

electron: A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.

filter: (n.) Something that allows some materials to pass through but not others, based on their size or some other feature. (v.) The process of screening some things out on the basis of traits such as size, density, electric charge. (adj. filtration)

flu: Short for influenza. A highly contagious viral infection of the respiratory passages causing fever and severe aching. It often occurs as an epidemic.

HEPA: An acronym for high-efficiency particulate air. It's a term for a type of pleated air filter (usually made of cloth). It can theoretically remove at least 99.97 percent of airborne particles that are at least 0.3 microns in diameter. That includes most bacteria, dust, mold and pollen. Any particles that are larger or smaller may be trapped even more efficiently. Such filters are often used on vacuums, ventilation systems and as covers to protect the nose and mouth.

immune system: The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

infection: A disease that can spread from one organism to another. It’s usually caused by some type of microbe.

link: A connection between two people or things.

liquid: A material that flows freely but keeps a constant volume, like water or oil.

nasal: Having to do with the nose.

particle: A minute amount of something.

PCR: An acronym for polymerase chain reaction. It's a biochemical process that repeatedly copies a particular sequence of DNA.

protein: A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Antibodies, hemoglobin and enzymes are all examples of proteins. Medicines frequently work by latching onto proteins.

SARS-CoV-2: A coronavirus that emerged in Wuhan, China, in late December 2019. It would go on to cause widespread — and sometimes lethal — disease throughout China and many other nations. Its name reflects its close similarity to the original coronavirus known as SARS (for severe acute respiratory syndrome). That SARS virus sparked a global outbreak of disease in 2003.

system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body's circulatory system. Similarly, trains, platforms, tracks, roadway signals and overpasses are among the potential components of a nation's railway system. System can even be applied to the processes or ideas that are part of some method or ordered set of procedures for getting a task done.

virus: Tiny infectious particles consisting of genetic material (RNA or DNA) surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact many scientists argue that no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.

voltage: A force associated with an electric current that is measured in units known as volts. Power companies use high voltage to move electric power over long distances.

Journal: J.V. Puthussery et al. Real-time environmental surveillance of SARS-CoV-2 aerosols. Nature Communications. Vol. 14, published online July 10, 2023. doi: 10.1038/s41467-023-39419-z.

Tina Hesman Saey is a senior staff writer and reports on molecular biology at Science News. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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