New device detects airborne Covid particles in minutes

Engineers have developed an ultra-sensitive device that can scan for Covid and other virus particles in indoor environments, in real time.

Researchers at Washington University in St Louis combined advances in aerosol sampling and an ultrasensitive biosensing technique to create the monitor, which can detect any variant of SARS-CoV-2 in a room in around five minutes. 

The device, which is still currently a proof of concept, could be used in hospitals and health care facilities to detect respiratory viruses such as Covid, influenza and respiratory syncytial virus. 

“There is nothing at the moment that tells us how safe a room is,” says  John Cirrito, a professor of neurology at the School of Medicine, who worked with researchers at the university's McKelvey School of Engineering. “If you are in a room with 100 people, you don’t want to find out five days later whether you could be sick or not. The idea with this device is that you can know essentially in real time, or every 5 minutes, if there is a live virus.”

Cirrito and colleague Carla Yuede have created a micro-immunoelectrode biosensor that can detect amyloid beta as a marker for Alzheimer's and wondered whether it could be repurposed as a Covid detector. They contacted Rajan Chakrabarty, a professor of energy, environmental and chemical engineering, who enlisted postdoctoral researcher Joseph Puthussery, who had expertise in building instruments that measure air toxicity. 

The researchers changed the antibody that recognises amyloid beta and swapped it for a 'nanobody' from llamas that is sensitive to Covid's spike protein. “The nanobody-based electrochemical approach is faster at detecting the virus because it doesn’t need a reagent or a lot of processing steps,” Yuede said. “SARS-CoV-2 binds to the nanobodies on the surface, and we can induce oxidation of tyrosines on the surface of the virus using a technique called square wave voltammetry to get a measurement of the amount of virus in the sample.”

Then they integrated the biosensor into an air sampler that employs 'wet cyclone technology'. Air enters the sampler at high speed and mixes with fluid that lines the walls of the sampler, creating a surface vortex that traps the virus aerosols. An automated pump collects the fluid and sends it to the biosensor. 

“The challenge with airborne aerosol detectors is that the level of virus in the indoor air is so diluted that it even pushes toward the limit of detection of polymerase chain reaction (PCR) and is like finding a needle in a haystack,” Chakrabarty said. “The high virus recovery by the wet cyclone can be attributed to its extremely high flow rate, which allows it to sample a larger volume of air over a 5-minute sample collection compared with commercially available samplers.”

The device is compact, at about a foot wide and 10 inches tall, and it lights up when a virus is detected, alerting administrators to improve airflow and circulation in the room. It has a flow rate of 1000 litres a minute, much higher than existing devices. 

The device was tested in the apartments of two COVID-positive patients, and two virus-free control rooms and was able to detect differences in virus levels after only a few minutes. “We are starting with SARS-CoV-2, but there are plans to also measure influenza, RSV, rhinovirus and other top pathogens that routinely infect people,” Cirrito said. “In a hospital setting, the monitor could be used to measure for staph or strep, which cause all kinds of complications for patients. This could really have a major impact on people’s health.”

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