Developed by researchers at Washington University in St. Louis, the inexpensive, proof-of-concept device is claimed to be the most sensitive detector available with the potential to monitor for other respiratory virus aerosols. The team’s work is detailed in Nature Communications.
The research team from the McKelvey School of Engineering and the School of Medicine consists of Rajan Chakrabarty, the Harold D. Jolley Career Development Associate Professor of energy, environmental & chemical engineering in McKelvey Engineering; Joseph Puthussery, a postdoctoral research associate in Chakrabarty’s lab; John Cirrito, professor of neurology; and Carla Yuede, associate professor of psychiatry, both at the School of Medicine.
“There is nothing at the moment that tells us how safe a room is,” Cirrito said in a statement. “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 five 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 disease. They wondered if it could be converted into a detector for SARS-CoV-2 and contacted Chakrabarty, who assembled a team including Puthussery, who has expertise in building real-time instruments to measure the toxicity of air.
To convert the biosensor from detecting amyloid beta to coronavirus, the researchers exchanged the antibody that recognises amyloid beta for a nanobody from llamas that recognises the spike protein from the SARS-CoV-2 virus. David Brody, MD, PhD, a former faculty member in the Department of Neurology at the School of Medicine and an author of the paper, developed the nanobody in his lab at the US National Institutes of Health. The nanobody is small, easy to reproduce and modify and inexpensive to make, according to the researchers.
“The nanobody-based electrochemical approach is faster at detecting the virus because it doesn’t need a reagent or a lot of processing steps,” said Yuede. “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 integrated the biosensor into an air sampler whose operation is based on wet cyclone technology. Air enters the sampler at very high velocities and gets mixed centrifugally with the fluid that lines the walls of the sampler to create a surface vortex, which traps the virus aerosols. The wet cyclone sampler has an automated pump that collects the fluid and sends it to the biosensor for detection of the virus via electrochemistry.
“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,” said Chakrabarty. “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 five-minute sample collection compared with commercially available samplers.”
Most commercial bioaerosol samplers operate at relatively low flow rates, Puthussery said, while the team’s monitor has a flow rate of about 1,000 litres per minute. It is also compact at about one foot wide and 10 inches tall and lights up when a virus is detected, alerting administrators to increase airflow or circulation in the room.
The team tested the monitor in the apartments of two COVID-positive patients. The real-time PCR results of air samples from the bedrooms were compared with air samples collected from a virus-free control room. The devices detected RNA of the virus in the air samples from the bedrooms but did not detect any in the control air samples.
In laboratory experiments that aerosolised SARS-CoV-2 into a room-sized chamber, the wet cyclone and biosensor were able to detect varying levels of airborne virus concentrations after only a few minutes of sampling.
“We are starting with SARS-COV-2, but there are plans to also measure influenza, RSV [respiratory syncytial virus], rhinovirus and other top pathogens that routinely infect people,” said Cirrito.
The team is working to commercialise the air quality monitor.