The team at Washington University in St. Louis combined recent advances in aerosol sampling technology and an ultrasensitive biosensing technique to develop this new device, which is able to detect any of the SARS-CoV-2 virus variants in a room in around five minutes.
The device is cheap to produce and can monitor the presence of a virus in a room in real-time. In addition to Covid-19, it could also be used to prevent the spread of other respiratory virus aerosols, such as influenza and respiratory syncytial virus (RSV).
"There is nothing at the moment that tells us how safe a room is," said Professor John Cirrito, one of the study's authors."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."
The team based their design on micro-immunoelectrode (MIE) biosensor that detects amyloid beta as a biomarker for Alzheimer's disease.
The researchers wondered if the sensor could be converted into a detector for SARS-CoV-2, and began researching in that direction, adding team members with 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 recognizes amyloid beta for a nanobody from llamas that recognizes the spike protein from the SARS-CoV-2 virus.
The nanobody is small, easy to reproduce and modify and inexpensive to make, the researchers said.
"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 associate professor Carla Yuede, another of the study's authors.
"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."
The team then integrated the biosensor into an air sampler that operates based on the wet cyclone technology, by which air enters the sampler at very high velocities and gets mixed with the fluid that lines the walls of the sampler to create a surface vortex, thereby trapping the virus aerosols.
The wet cyclone sampler has an automated pump that collects the fluid and sends it to the biosensor for seamless detection of the virus using 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 associate professor Rajan 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."
At the moment, most commercial bioaerosol samplers operate at relatively low flow rates, the researchers said. In contrast, the team's monitor has a flow rate of about 1,000 liters per minute, making it one of the highest flow-rate devices available.
The device is also compact at about 1 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 aerosolized 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, 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."
The research was published on the journal Nature.
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