Air Monitors Dan Detect COVID-19 Variants in 5 Minutes

Scientists are investigating strategies to detect viruses in indoor spaces in real time now that the COVID-19 pandemic’s emergency phase has finished. Researchers at Washington University in St. Louis have developed real-time air monitors that can detect any of the SARS-CoV-2 virus subtypes in a room in roughly 5 minutes by combining recent breakthroughs in aerosol sampling technology and an ultrasensitive biosensing technique.

The low-cost proof-of-concept device might be utilized in hospitals and health care facilities, as well as schools and public areas, to detect CoV-2 and potentially monitor for other respiratory viral aerosols including influenza and respiratory syncytial virus (RSV). Nature Communications released the results of their work on the monitor, which they claim is the most sensitive detector available.

Rajan Chakrabarty, the Harold D. Jolley Career Development Associate Professor of energy, environmental, and chemical engineering in McKelvey Engineering; Joseph Puthussery, a postdoctoral research associate in Chakrabarty’s lab; John Cirrito, a professor of neurology at the School of Medicine; and Carla Yuede, an associate professor of psychiatry at the School of Medicine, comprise the interdisciplinary team of researchers.

“There is nothing at the moment that tells us how safe a room is,” Cirrito said. “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 Yuede had previously developed a micro-immunoelectrode (MIE) biosensor that detects amyloid beta as a biomarker for Alzheimer’s illness and were curious if it might be transformed into a SARS-CoV-2 detector. They contacted Chakrabarty, who put together a team that included Puthussery, who had experience designing real-time sensors to monitor air pollution.

The researchers swapped the antibody that detects amyloid beta for a nanobody from llamas that recognizes the spike protein from the SARS-CoV-2 virus to switch the biosensor from detecting amyloid beta to coronavirus. The nanobody was developed in the lab of David Brody, MD, Ph.D., a former faculty member in the Department of Neurology at the School of Medicine and one of the paper’s authors. According to the researchers, the nanobody is small, easy to replicate and modify, and inexpensive to build.

“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.”

Chakrabarty and Puthussery built the biosensor into an air sampler that uses wet cyclone technology. Air enters the sampler at high speeds and mixes centrifugally with the fluid that lines the sampler’s walls, creating a surface vortex that traps virus aerosols. The wet cyclone sampler has an automated pump that collects the fluid and transfers it to the biosensor for electrochemical detection of the virus.

“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.”

According to Puthussery, most commercial bioaerosol samplers have very low flow rates, whereas the team’s monitor has a flow rate of around 1,000 liters per minute, making it one of the highest flow-rate devices available. It is also small, measuring approximately 1 foot wide and 10 inches tall, and it illuminates when a virus is discovered, notifying administrators to enhance ventilation or circulation in the space.

The air monitors was tested in the apartments of two COVID-positive patients. The results of real-time PCR on air samples from the bedrooms were compared to air samples from a virus-free control room. The instruments found viral RNA in the air samples from the bedrooms but not in the control air samples.

The wet cyclone and biosensor were able to identify various levels of airborne virus concentrations after only a few minutes of sampling in laboratory studies that aerosolized SARS-CoV-2 into a room-sized container.

“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 air monitors 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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