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Penn Medicine Researchers Targeting Broad SARS-CoV-2 Testing With Four-Minute, $5 Biosensor


NEW YORK ─ Penn Medicine researchers are developing a four-minute test that costs less than $5 to produce and could enable broad SARS-CoV-2 testing during and after the current pandemic, according to its developers.

Seeing a continuing need for fast, inexpensive SARS-CoV-2 testing at the point of care, they printed electronic inks on filter paper to make a biosensor that detects an electrochemical charge in response to the presence of SARS-CoV-2 spike proteins in a swab or saliva sample.

The group said in a recent clinical study of the test's performance published in Matter that the fabrication technique they used to print the biosensor could enable testing in high volumes where testing laboratories are scarce.

The test, called Rapid 1.0, is a handheld biosensor that employs human receptor angiotensin-converting enzyme-2, or ACE2, to detect SARS-CoV-2 using saliva or a nasal sample. It employs an electrochemical technique called impedance spectroscopy to detect an electrical signal in response to the binding of the SARS-CoV-2 spike protein to ACE2.

"With Rapid 1.0, we decided to mimic the way that SARS-CoV-2 enters the body where it binds to ACE2, its human receptor," said César de la Fuente, who is a Penn Medicine presidential assistant professor in psychiatry, microbiology, chemical and biomolecular engineering, and bioengineering, and who is also leading the development of the test.

The Penn Medicine group is in discussions with the US Food and Drug Administration about the requirements for applying for Emergency Use Authorization that would enable it to market the test, de la Fuente said, adding that he and his colleagues believe the biosensor will become one among a repertoire of tools to help people attend events, travel, and safely get back to work during the pandemic.

Though laboratory-based RT-PCR testing has been the go-to modality to test for active SARS-CoV-2 infections, antigen tests and point-of-care PCR tests that provide faster turnaround times are also being deployed. Test technologies that enable rapid turnaround and frequent testing are seen by some as a way to screen large numbers of people.

"I'm a proponent of frequent testing, and one of the things we need to enable it is low-cost technology," de la Fuente said. "If you use a test like Rapid 1.0 a few times throughout the week, you are going to be able to track your COVID-19 status with a high level of accuracy and close to real time."

The Penn Medicine group uses a fabrication method called screen printing, a major contributor to the potential for high-volume production and low production costs. The test's electrodes can be quickly mass produced using commercially available screen printers. To show the technique's scalability, the group produced 35,000 electrodes in the lab in one day, de la Fuente said, adding that the test's materials — filter paper and recyclable plastics — are also cheap.

Overall, the combination of materials, fabrication process, analytical performance, rapid turnaround, and operation at room temperature can lead to a commercial test that has the potential to reduce production costs as well as challenges related to scalability and test turnaround times, de la Fuente said.

"One thing that we've always tried to do is make the test as cheap as possible, so that many people can afford it — not only people with economic means but also those living in in low-resource settings and in developing countries," he said. "About 95 percent of the current cost of the test comes from the receptor, but that is because we don't have the facilities here to produce it at a large scale, which would further drive down the cost."

The researchers envision their platform being used in high volumes to test people in schools, airports, stadiums, company buildings, and in the home.

"The healthcare divide between resource-rich and poor countries supports the need for robust, yet accessible diagnostic technologies," Cesar Castro, associate professor of medicine at Harvard Medical School, said in an interview.

Such tests require low cost, automated readouts and interpretation, and ease of use for lay people, he noted.

The Penn Medicine researchers "seemingly check the boxes on all fronts," said Castro, who is not involved in developing the test. "Importantly, great attention to detail even at the manufacturing level bodes well for eventual clinical adoption once the assays are further validated."

The Philadelphia-based research team evaluated the clinical performance of the biosensor test using both COVID-19-positive and -negative clinical samples from Penn Medicine's Hospital of the University of Pennsylvania, including samples of the B.1.1.7 variant first detected in the UK, which is thought to be more contagious than the original strain of the virus. In blinded tests, they analyzed 139 nasopharyngeal or oropharyngeal swab samples. One hundred and nine were determined to be COVID-19-positive and 30 were COVID-19-negative by RT-PCR testing. The researchers also evaluated the test using 50 saliva samples.

Rapid 1.0 had 85.3 percent sensitivity and 100 percent specificity using either nasopharyngeal or oropharyngeal swabs, and 100 percent sensitivity and 86.5 percent specificity using saliva samples, the researchers found.

"In this small clinical subset, the assay performance was robust, [and] the most promising results occurred following storage at minus 20 degrees Celsius," Castro said, adding that the biosensors retained high levels of performance at room temperature when they were used in less than 24 hours after printing and, as a result, may be well suited for printing on-site.

Castro added that the sensitivities reported in the study "are extremely high for affinity-based viral detection. This is more impressive given the four-minute incubation period [because] a very large number of viral particles would have to diffuse to the electrodes to achieve such results within that time period."

Ultimately, whether the test takes four minutes or can be completed in less than one hour, "such near-patient testing with low-cost tools could be a means to empower marginalized populations and democratize healthcare through increased decentralization," Castro said.

The Penn Medicine researchers noted that Rapid 1.0 detects SARS-CoV-2 at low concentrations, down to 1.16 PFU mL, which translates to detecting viral loads that correlate with the initial stages of COVID-19, and would enable the screening of people who are asymptomatic.

The group is working on two versions of the test. One version — suitable for over-the-counter and at-home testing — plugs into a smartphone that uses an app to display results. The second version is designed for testing in buildings or CLIA-certified labs and displays results on a desktop computer.

The smartphone version requires a one-time purchase of a small potentiometer to enable detection, which is likely to cost about $100, de la Fuente said. The desktop version requires a larger potentiometer that would require a one-time purchase of a few thousand dollars unless the group can find a partner to help it develop a cheaper device. The disposable cartridge used for testing should cost less than $5, he said.

The Penn Medicine group is considering launching a startup to commercialize the test and has its sights set on obtaining FDA 510(k) clearance. "Our primary goal is to provide a commercial test that can be helpful for people in the context of this terrible pandemic that we are still living through, and so a 510(k) clearance would be a more permanent way than EUA of doing that," de la Fuente said.

The Penn Medicine group is also exploring additional medical indications for its platform, and it is developing tests to detect herpes and influenza viruses and starting to explore the detection of infectious disease-causing bacteria.