A team used to making pollutant detectors is adapting their systems to identify coronavirus in air.

Formerly dedicated to creating technologies that spot aerosols and artificial nanoparticles, researchers from the Swiss Federal Laboratories for Materials Science and Technology (EMPA), Swiss Federal Institute of Technology in Zurich (ETH Zurich), and Zurich University Hospital have developed a biosensor  specifically ready to pick up the RNA genome of SRA-Cov-2.

While the biosensor is not an alternative to clinical diagnostics, the scientists see the system potentially operating in crowded environments.

"For ease of use, the integrated system will be a portable device that can be used for rapid detection in public areas, such as train stations and hospitals," ETH Zurich postdoctoral researcher Guangyu Qiu told Tech Briefs.

To detect the virus safely and reliably, the sensor combines two different effects: optical and thermal.

Because the coronavirus genome is a single RNA strand, the sensor features artificially produced DNA receptors that match specific RNA sequences of the SRA-CoV-2. The recepters are grafted on the sensor's gold "nanoislands," which are placed on a glass substrate.

The biosensor relies on an optical phenomenon known as localized surface plasmon resonance, or LSPR. The metallic nanostructures, when excited, modulate the incident light in a specific wavelength range and create a plasmonic near-field around the nanostructure.

When molecules bind to the surface, the local refractive index within the excited plasmonic near-field changes. An optical sensor, located on the back of the sensor, measures the change and thus determines whether the sample contains the RNA strands in question.

The thermal aspect of the sensor offers secondary confirmation of detection. To maintain a constant high temperature to eliminate nonspecific bindings, a laser is applied to the sensor during the whole detection process.

The plasmonic photothermal (PPT) effect produces localized heat and raises ambient temperature, allowing only the RNA strands of the virus to join with the nanoisland receptors.

a diagram of the biosensor from ETH Zurich and its photothermal (PPT) heating effect
Schematic illustration of the dual-functional plasmonic biosensors for accurate SARS-CoV-2 detection. The right-top inset shows the in situ temperature profile of plasmonic photothermal (PPT) heating. The right-down inset demonstrates plasmonic biosensing performance on detecting different viral sequences.

To demonstrate the sensor's reliability, the team, led by ETH Zurich Prof. Jing Wang and ETH Zurich postdoctoral researcher Guangyu Qiu, tested their sensor's ability to detect SARS-CoV, a closely related virus. SARS-CoV, which broke out in 2003 and triggered the SARS pandemic, differs only slightly from the SRA-CoV-2 virus in its RNA.

Tests showed that the sensor can clearly distinguish between the very similar RNA sequences of the two viruses.

The research plan began in mid-January, and the biosensor is still in development.

"At present, the only developed prototype is still in the laboratory level," said Qiu. "These are more fundamental works that need to be continued before practical application and mass production."

In a short Q&A with Tech Briefs below, Guangyu Qiu explains what kind of development works needs to happen before we see the biosensor in hospitals and train stations.

Tech Briefs: This sensor could potentially be used in places with many people. Can you bring us into a scenario that you envision? How could this be used in the future?

Guangyu Qiu: Our proposed dual-functional plasmonic technology can accurately discriminate against the viral sequence and perform quantitative detection. Therefore, we hope that it can be applied to study the transmission of airborne viruses and assess the virus threat in the air. To achieve this aim, it requires a fully integrated system. This system will contain several important subunits including the air sampling unit and this developed biosensors. For ease of use, the integrated system will be a portable device that can be used for rapid detection in public areas, such as train stations and hospitals.

Tech Briefs: What kinds of development work need to happen before we see this used? What are you working on now?

Guangyu Qiu: We need to further integrate the air sampling unit and biological processing unit into the final system. These two subunits can facilitate the online fast detection of airborne virus by collecting the airborne virus and extracting the viral sequence. We are currently working on these developmental works in parallel.

Tech Briefs: Do you have any advice for engineers who are looking to build technologies to help the response to COVID-19 (or any other global challenge)

Guangyu Qiu: At present, this new type of optical sensor has demonstrated its practical potential. We hope that more efforts can participate in the development of similar novel technologies. Although some of these emerging technologies cannot be put into use in the short term, more participation in scientific research will definitely speed up their development.