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University of Florida Team Crafts 30-Second COVID-19 Saliva Test Based on Electrical Current


NEW YORK – Researchers from the University of Florida have developed a rapid test for SARS-CoV-2 that uses electric current to measure the presence of the virus in a saliva sample.

The team has licensed the technology to Houndstoothe Analytics, which expects to submit the test to the US Food and Drug Administration for Emergency Use Authorization later this year. 

Fan Ren, a professor in University of Florida's department of chemical engineering and one of the test developers, has been working on using sensors for healthcare applications for more than 10 years, but once the pandemic hit, he and his team applied their technology to COVID-19. 

Ren and one of his co-developers Josephine Esquivel-Upshaw, a professor in UF's college of dentistry, have been working together for about eight years, and the sensor technology used in the test was originally applied to troponin measurements for heart attacks. In 2020, Ren's team brought up the idea of using the tech for COVID-19, although they initially began developing the test for use with nasopharyngeal samples. Esquivel-Upshaw's expertise as a dentist led her to question whether saliva as a sample type might be better, so she and the team investigated further whether saliva would work as a sample type.

The assay uses a disposable strip — similar to those used for glucose detection, although without the glucose enzyme on it — that has been gold plated and biofunctionalized and contains SARS-CoV-2 antibodies connected to a reusable circuit board. The circuit board includes a transistor, which amplifies the signal of the reaction when the test is run. If a saliva sample with the virus has been placed on the strip, the antibodies and the virus will bind together, Ren said. After the sample is on the strip, an electrical current is run through the device and the strip, and that current excites the antibody-antigen pair and causes them to "stretch and twist," Esquivel-Upshaw said.

Rather than detecting the actual virus molecules, the test measures electrical energy and the change in that energy to determine the presence of SARS-CoV-2, she added. Those changes have been converted to digital readouts that show not only the presence of the virus, but also the concentration of virus in that sample. The higher the concentration, the larger the pulse, Ren said.

In a study published in February in the Journal of Vacuum Science and Technology, the team looked at 60 saliva samples that had been tested via RT-PCR and had cycle threshold (Ct) values determined and then used their test on those same samples. The test was able to differentiate between samples with Ct values ranging from 17.8 to 35, indicating low concentrations of viral particles. According to the researchers, the study showed that "the sensor technology has a lower limit of detection compared with commercial lateral flow tests, which are only sensitive for samples that consist of high virus concentrations." 

Other companies and researchers have also used electrochemical reactions to detect SARS-CoV-2. IdentifySensors Biologics, a Cleveland-based company, is working on a five-minute biosensor-based COVID-19 test that measures changes in electrical currents that indicate the presence of the virus, although the test does take longer than the UF test. Researchers at the National Institute of Animal Biotechnology in India, meantime, have also developed an electrochemical sensor-based test for SARS-CoV-2 that measures electrical conductivity.

One issue with using saliva, Esquivel-Upshaw said, is that it "houses everything." Currently, the team is running studies to check for cross-reactivity so they can ensure that only SARS-CoV-2 is being detected and the presence of other molecules isn't impacting the test's performance.

A key benefit of the SARS-CoV-2 test that both Ren and Esquivel-Upshaw noted is its relatively low cost. The circuit boards come from offshore suppliers and cost $40 but could get as low as $25 for large orders, and the strips themselves cost between 10 and 12 cents per strip. The circuit board cost would be a one-time expense, Ren added.

Ren and Esquivel-Upshaw see the test being used at the point of care and potentially at home and are working with biotechnology company Houndstoothe Analytics to shepherd the assay through the commercialization process. Houndstoothe recently licensed the test in an exclusive global agreement with the University of Florida and is working on getting the test submitted to the FDA for EUA in about the next six months, said John Nosta, one of Houndstoothe's founders.

Nosta echoed Ren and Esquivel-Upshaw's expectations for use at the point of care, although the company doesn't necessarily have a "hard and fast target" for its use case. 

"We may be able to craft a test that can be useful at home, in the field … in the emergency room, or even in the hospital," Nosta said, adding the company isn't sure what the test will cost once it's on the market but estimated it would be less than $100, cheaper than most molecular tests. "The market doesn't need an expensive COVID-19 test — we already have that," he said. 

The firm has had "very, very preliminary" conversations with a variety of potential distribution and marketing partners and believes it is in Houndstoothe's "best interest" to partner with another company because "in healthcare, market access is a difficult and complicated dynamic." A larger company may also have a global footprint, allowing the test to be launched in other countries. "We recognize that we are a small company with a big idea," Nosta noted.

While saliva may be the testing medium of choice for the SARS-CoV-2 test, Esquivel-Upshaw noted that the technology can be used for virtually any body fluid, including plasma and nasal discharge. It has been used not only to measure troponin, but also to detect Zika virus. The team is also working on applications in breast and oral cancer. It can also be used as a pH sensor, Ren added, which would be helpful for diseases like pneumonia and asthma, where the pH value of a breath sample correlates to the severity of the disease. The team also wants to use the technology to study environmental contamination, such as oil spills, Ren said.

The technology's other applications are a focus of Houndstoothe's, as well. Nosta said that the quantitative aspect of the SARS-CoV-2 test could be used to measure a patient's immunological status to determine their immunity to COVID-19 or to provide guidance on managing patients on immunosuppressant agents. The changes in the electric current correspond to the amount of a particular protein, such as immunoglobulin G, and in this case would measure a certain marker for immunological status, Nosta said. "It would not directly detect an immune response but an immune status."

He added that the company is looking at some early data for its use with troponin and putting together a "clinical path forward" for that test. The firm is also exploring cancer testing and how the technology could potentially be used to detect cancer-related biomarkers in saliva, as well as other bioactive proteins in fluids like urine.

The ability to apply the technology to other fluids, as well as its speed and low cost, could make it a kind of "holy grail" in the diagnostics industry, Ren said. "This is going to change the medical industry … it can help so many people."