NEW YORK ─ University of Illinois at Chicago researchers are leveraging graphene, a nanomaterial with exceptional strength and conductivity, to develop diagnostic tests for SARS-CoV-2 active infection and other indications.
In a study published recently in ACS Nano, the researchers described a new chemistry process to grow antibodies that detect the SARS-CoV-2 spike protein on the surface of graphene.
A central component of the diagnostic test, graphene is inexpensive to produce, easy to fabricate, and has unique properties, said Vikas Berry, head of chemical engineering at the UIC College of Engineering and lead author of the study.
Developers can leverage graphene's properties for diagnostic tests that are highly sensitive to the presence of a target analyte for a broad range of diagnostic applications, he added. The UIC group used saliva samples and the graphene biosensor in a research laboratory to detect the SARS-CoV-2 spike protein with a limit of detection of less than 4 pg/mL.
That is competitive with levels for current antigen tests that have received US Food and Drug Administration Emergency Use Authorization, Berry said, adding that as a result he and his colleagues are moving ahead with commercialization of a point-of-care test and eventual FDA EUA application.
The graphene biosensor uses a vibration signature, also known as a phononic signature, along with Raman spectroscopy and saliva samples. Such a combination lends itself to the detection of COVID-19 antigens and its variants of concern, as well as antigens and antibodies for many diagnostic applications, Berry said.
In the SARS-CoV-2 antigen test, the group adheres antibodies to the graphene surface that are specific to the virus' spike protein. Graphene's atoms vibrate at frequencies that correlate with the presence of infection and can therefore be detected by spectroscopy. Because the material is so thin — consisting of a layer of linked single carbon atoms — "we can detect almost anything that has the potential to produce a phononic change," Berry said.
A UIC-developed process to treat the surface of graphene is one of the keys to the platform's potential for broad applicability, and makes it easier to attach antibodies or antigens that have a specific affinity for selected target analytes. The process preserves the phononic properties of graphene, which is highly sensitive to any contact, Berry said, adding that detection antibodies are adhered to the surface without creating defects or scattering sites for electrons.
Similar to many biosensor platforms in development for diagnostic applications, the UIC device lends itself to the development of many different types of tests.
The UIC researchers have conducted preliminary studies using cerebrospinal fluid to show that the platform can detect the presence of glioblastoma and, separately, amyotrophic lateral sclerosis, and they continue to develop the platform for those indications.
"The combination of phononic modification in antibody-coupled graphene with Raman spectroscopy may offer new possibilities for the label-free detection of various analytes," said Giuseppe Spoto, a professor of chemical sciences at the University of Catania in Italy who is developing a liquid biopsy assay for cancer detection that uses plasmonic biosensing, involving the oscillation of plasma.
Both types of systems employ optical sensing "and hold potential for the ultra-sensitive detection of analytes dispersed in complex matrices such as blood plasma and saliva," said Spoto, who is not affiliated with the UIC group. Moving the UIC approach to the market would require "optimized, efficient, and reproducible production of the functionalized graphene layer, specifically designed for the selected application," Spoto said. "Such a step is undoubtedly challenging, but it may deserve the required efforts since applications may span a wide range."
Berry and his colleagues use methane to grow graphene on sheets of copper — a process they believe can be used to inexpensively manufacture point-of-care diagnostic tests on a mass scale.
According to Ngoc Hoang Lan Nguyen, a UIC researcher, graduate student, and a developer of the graphene test, the group may be the first to use phononic signatures for the development of a testing platform. While other developers have exploited electrons and photons for detection, the use of phonons in diagnostic testing has gone largely unexplored, Nguyen said in an interview. Though a main aspect of the ACS Nano study is the development of a COVID-19 biosensor, the use of phononic signatures for diagnostic testing applications may inspire others to start developing tests based on the effect, Nguyen said.
If the UIC group can commercialize the biosensor, its use of copper and methane as the primary materials will contribute significantly to affordability, she said. The group spent $1,000 on a cylinder of methane one year ago, and it is still using it for fabrication and development. Copper, meanwhile, is cheap and plentiful, and the group can grow around 2,000 biosensors on a piece of foil measuring 6 by 12 inches.
Interest in graphene
The UIC researchers are among a growing pool of developers using graphene for potential high-performance diagnostic tests. Spoto noted that extensive research is being conducted to take advantage of the material's superior properties.
In February, an international research group announced it is developing a testing platform that uses an inexpensive laser to fabricate detection electrodes from graphene and DNA aptamers as substitutes for antibodies to target analytes of interest.
In 2019, Roche Diagnostics took over development of a proof-of-principle prototype that uses graphene and field effect transistors for point-of-care testing, and University of Michigan researchers announced that they are developing a wearable device that can continually collect circulating tumor cells in the blood using a herringbone graphene oxide microfluidic chip to maximize the contact frequency of cells.
The UIC group is in discussions with a few diagnostic industry companies about commercialization, including one undisclosed developer of spectroscopic imaging equipment, Berry said.
Its next steps involve further development followed by the start of a clinical trial to validate the sensitivity and specificity of the platform and SARS-CoV-2 test. The group needs to develop an automated process to analyze and interpret the output of the platform's Raman spectroscope, which would enable it to decide within minutes whether a SARS-CoV-2 infection is present in a saliva sample.
If UIC finds a suitable industry collaborator, the device could be ready for an EUA application within about two months, Berry said. The researchers may instead spin out a startup, which would delay an application for EUA by about four months, he added.