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U of Maryland Team Developing Biosensor for Early Detection of SARS-CoV-2 Infection

NEW YORK ─ Researchers at the University of Maryland School of Medicine (UMSOM) have developed a biosensor that they said could soon be available to test for SARS-CoV-2 alongside current molecular, antibody, and antigen tests.

Leveraging plasmonic properties of gold nanoparticles that cluster around viral RNA molecules, the biosensor changes colors to indicate the presence of SARS-CoV-2. Described in a recent study published in ACS Nano, the researchers said that their colorimetric assay has the potential to be used as a screening test.

According to Dipanjan Pan – who is leading the test's development and is a professor of diagnostic radiology, nuclear medicine, and pediatrics at UMSOM – clinicians struggling to mitigate the COVID-19 pandemic need more rapid, convenient, and affordable tools that can be deployed on a large scale at the point of care to detect active disease.

With that in mind, he and his colleagues developed a prototype that they believe could be deployed in the next few months as a diagnostic test for SARS-CoV-2, though further development, validation, and scale up for manufacturing will be required.

The biosensor uses a simple assay containing plasmonic gold nanoparticles to detect a color change when the virus is present, Pan said, adding use of the plasmonic gold nanoparticles is far simpler and more affordable than the standard isothermal amplification methods that current tests use to detect the presence of the infection.

To develop the test, the researchers at UMSOM designed thiol-modified antisense oligonucleotides that are specific to the N-gene of SARS-CoV-2. In the presence of target SARS-CoV-2 RNA sequences, gold nanoparticles that are capped with thiol-modified antisense oligonucleotides form clusters causing changes in surface plasmon resonance. That alteration then manifests as a color change in the assay that indicates the presence of the infection.

The developers of the biosensor-based test believe its availability could help mitigate challenges associated with testing supplies, including reagents to run tests, and resources, including a scarcity of trained lab personnel.

Pan said he anticipates the point-of-care test will have a place alongside current technologies and tests that clinicians are already using to try to handle demand during the pandemic.

To date, several dozen tests using RT-PCR have received Emergency Use Authorization from the US Food and Drug Administration to diagnose COVID-19. About a dozen serology tests and one rapid protein antigen test have also been issued EUA by the agency, as have a handful of decentralized tests, including molecular ones by Cepheid Xpert Xpress and Abbott ID Now.

Despite the availability of such tests, the lack of accessibility to them, particularly in remote areas, remains  a barrier to broad-scale testing, Pan said.

Sherwood Yao, the cofounder of Research Triangle Park, North Carolina-based Atom Bioworks, said in an interview that problems associated with current diagnostic approaches in the context of the pandemic are clear. "These approaches usually require large central lab instruments, and test protocols are complex," he said. As a result, "we strive to find novel ways to build a biosensor assay that is easy to use."

Yao is not involved in the biosensor development work at the University of Maryland. His firm recently was awarded a $248,000 National Science Foundation grant to use artificial intelligence and nanotechnology to design a rapid diagnostic test for SARS-CoV-2.

He said that Pan and his colleagues' choice of gold nanoparticles and sequence-specific binding for colorimetric signal generation "is well established in biosensor design, and once developed, the N-gene sequence targeted binding should provide good specificity."

The UMSOM test is "simple to perform without the need of large instruments," he said but noted "we are not certain of its performance and in particular its sensitivity and its claim to reliably detect" early infection in patients.

Pan agreed that while preliminary results suggest its biosensor may be able to detect viral RNA early in the infection cycle, additional studies are needed to prove it. The limit of detection of its assay is "roughly comparable" with that of RT-PCR, he said.

Its biosensor-based test will be most useful for point-of-care screening that requires rapid results for active infections, such as in airports, long-term care facilities, and community settings, Pan said.

The platform operates directly from a nasal swab or saliva sample that would be obtained from a patient by a healthcare professional. In addition to enabling convenient sampling methods, the platform's gold nanoparticle chemistry is well known and scalable at a reasonable cost, and oligos can be inexpensively synthesized, contributing to overall affordability, Pan said.

The group, whose work is funded by the University of Maryland, is preparing a pre-submission with a view to obtaining an EUA from the FDA. The researchers recently launched a company, VitruVian Bio, to commercialize their biosensor diagnostic technologies.

The firm, which is based in Baltimore, Maryland, had been focusing on the development and commercialization of a biosensor for traumatic brain injury, but it put that project aside and shifted its focus to commercializing the diagnostic test for SARS-CoV-2. It is looking to collaborate with a diagnostic firm interested in taking the technology to market, Pan said.