NEW YORK ─ Washington University in Saint Louis (WUSTL) researchers are developing a plasmonic sensor platform that they anticipate making available as a diagnostic test with improved sensitivity over current tests used to detect antibodies against SARS-CoV-2.
The platform, described recently in a study published in Nature Biomedical Engineering, has the potential to boost the limit of detection of diagnostic tests to the level of femtometers in a range of medical applications, including tests for acute kidney injury and myocardial infarction, as well as SARS-CoV-2, Srikanth Singamaneni, a study author and professor of mechanical engineering and materials science at WUSTL, said in an interview.
If the test can be commercialized, its higher sensitivity could enable clinicians and researchers to find positive cases earlier in the SARS-CoV-2 infection cycle and reduce the likelihood of false negatives occurring during testing, Singamaneni said.
He and his colleagues recently announced that they have received a $100,008 National Science Foundation grant toward developing a SARS-CoV-2 antibody assay for their platform using the plasmonic biosensor technology.
It is uncertain how early in the disease cycle the assay would be able to detect antibodies to SARS-CoV-2. However, the availability of a high-sensitivity antibody test such as that being developed at WUSTL "would be particularly important for use in epidemiological studies used to understand how widely the disease has spread," Singamaneni said. Further, the assay could reduce the amount of time it takes overall to do highly sensitive SARS-CoV-2 antibody testing, and its potential for use in a lateral flow format could enable testing at home, he added.
Among its most important elements, the biosensor prototype leverages a plasmonic nanoscale assembly, called a plasmonic fluor, that enhances fluoresence; a molecular light emitter called a fluorophore; and a universal biological recognition element, usually biotin. The plasmonic fluor increases sensitivity by combing the gold nanoparticles with fluorophores, or dyes, that are routinely used in diagnostic tests, Singamaneni said.
Because of the nanoscale assembly's fluorescence properties, the group is seeing sensitivity levels one hundredfold that of current ELISA-based tests that detect antibodies against SARS-CoV-2 or other infections, Singamaneni said.
Many diagnostic applications, such as early cancer detection, neurological disease, brain injury, and others can be improved by detecting more analytes in a sample, Brian Cunningham, a professor in engineering who leads a nanosensors group at the University of Illinois at Urbana-Champaign, said in an interview.
While he is not familiar with WUSTL's work on a SARS-CoV-2 assay, Cunningham said that generally, "the benefit of greater signals is that even for concentrations that are currently detectable they can be detected with better signal-to-noise with plasmonic fluors, which translates into a greater level of robustness."
The WUSTL plasmonic fluor technology described in the NBE study, which covers development of the testing platform but not work to develop the SARS-CoV-2 assay, represents a "highly effective means for amplifying the output of surface-based fluorescence assays," Cunningham said. "The [plasmonic fluor construct] can be reproducibly and uniformly fabricated over large surface areas, cut to any desired size, and easily manipulated to place onto glass slides, into the wells of microplates, or any other assay surface."
Many biosensor researchers are looking to use the properties of gold nanoparticles to improve diagnostic testing, said Giuseppe Spoto, a professor of chemical sciences at the University of Catania in Italy. His group, for example, has combined chemiluminescence with gold nanoparticles as part of a droplet microfluidic-based prototype to detect lysozyme, a bacteriolytic enzyme.
Singamaneni and his colleagues "convincingly demonstrate" the potential of their plasmonic fluor technology for "highly sensitive diagnostic assays," Spoto said, adding he could see the nano construct being developed "as part of the standard toolbox available to ELISA, flow cytometry, and other fluorescence-based platforms users."
The WUSTL group is working, for example, to incorporate its technology into a lateral flow testing format that has the potential for use in the home as a self-test, Singamaneni said. Further, the technology has the potential to reduce the time to conduct standard ELISA tests to less than 20 minutes compared to up to four hours for a standard ELISA test, he said.
Most highly sensitive antibody tests require a few hours to complete assays run in a laboratory by trained lab technicians, he said, adding that the shorter time to result for its technology may enable its use "at the point of care in resource-limited and other settings."
In addition to developing the technology to detect antibodies against SARS-CoV-2, the group is exploring other medical diagnostic applications, included the detection of antibodies associated with acute kidney injury and myocardial infarction.
In the NBE study, the group demonstrated that its plasmonic fluorophore enabled a limit of detection at least two orders of magnitude lower than that of an ELISA assay.
The researchers have licensed their platform technology to Saint Louis, Missouri-based Auragent Bioscience, a firm that Singamaneni cofounded. The company is scaling up production of the platform's nanoparticles and has so far synthesized liter-size quantities, he said.
Further, Auragent is seeking to develop the platform for a number of different types of testing systems. In addition to its potential for application as a substitute for enzymes in ELISA testing, the biosensor platform has the potential to improve the limit of detection in multiplexed bead-based immunoassays, immunomicroarrays, flow cytometry platforms, and immunocytochemistry tests, the researchers said.
Further, the company has licensed a plasmonic patch technology developed by Singamaneni and his colleagues at WUSTL and Wright-Patterson Air Force Base in Dayton, Ohio. The patch, using a technology different from the plasmonic fluor, also holds potential to improve the sensitivity of a broad range of research and clinical diagnostic tests, Singamaneni said. However, Auragent has set aside work on the plasmonic patch in favor of focusing on development of the plasmonic fluor platform.
The WUSTL platform, currently a prototype, will require further development and validation as well as manufacturing scale-up and potentially licensing to a diagnostics company before submission for regulatory approval, Singamaneni said.
Test developers who intend for their serology assays to be used to test for antibodies against SARS-CoV-2 are required to take their tests through the US Food and Drug Administration's Emergency Use Authorization process. Among high-throughput serology tests that have received EUA for the coronavirus are those from Roche, Abbott, and Ortho Clinical Diagnostics.
While it would compete with many antibody serology tests in the market, the WUSTL group believes that its test for antibodies against SARS-CoV-2 may become available later this year.
Among its near-term goals for further development, the group anticipates using about 30 patient samples to validate its SARS-CoV-2 assay on a preliminary basis in a project expected to last about three months, Singamaneni said.
The researchers are simultaneously looking to collaborate with a company "that can validate the technology on a larger number of patient samples" and can develop the test for clinical use, Singamaneni said. "We'll need clinical partners but more importantly, we will need to collaborate with people who have diagnostic industry experience in scaling up assays for production ─ both particle production and the testing has to be scaled up," he said.
While the low limit of detection points to higher sensitivity, the group also needs to ensure that the its SARS-CoV-2 assay has the highest possible specificity, Singamaneni said. The specificity of the test that he and his colleagues are developing has yet to be determined.
In addition to a test needing high sensitivity, high specificity is important because several common coronaviruses to which people already have antibodies could cross-react in an assay, leading to false positives, Singamaneni said. The researchers are analyzing antigens that are highly specific to SARS-CoV-2 to serve as a basis for developing and manufacturing high specificity antibodies, he said.