COVID-19 testing remains a top priority around the world as the pandemic continues, with scientists seeking new and better ways to conduct testing to detect, track and contain the virus.

To support this endeavor, researchers at the University of Illinois Urbana-Champaign have developed an ultrasensitive COVID test using a paper-based electrochemical sensor that can produce results in less than five minutes.

The test was developed by University of Illinois Urbana-Champaign graduate student Maha Alafeef, who said she has long been interested in using bioengineering to solve real-world problems.

“Currently, we are experiencing a once-in-a-century life-changing event,” she said in a press statement. “We are responding to this global need from a holistic approach by developing multidisciplinary tools for early detection and diagnosis and treatment for SARS-CoV-2.” 

Graphene Paves the Way

Currently, there are two key categories of tests for COVID-19, the most widely used being the reverse transcriptase real-time polymerase chain reaction (RT-PCR) test, which can provide results in a few days’ time.

The second category of tests focuses on the detection of antibodies, but this typically can’t be done until someone already is infected with the virus or even after recuperation as there can be a delay of a few days to a few weeks after a person has been exposed to the virus for them to produce detectable antibodies.

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The electrochemical sensing platform developed by Alafeef has its foundation in the use of graphene to detect diseases in point-of-care biosensors. These sensors are highly sensitive and can detect diseases rapidly without a high cost of production, researchers said.

“The discovery of graphene opened up a new era of sensor development due to its properties,” Alafeef explained in a press statement. “Graphene exhibits unique mechanical and electrochemical properties that make it ideal for the development of sensitive electrochemical sensors.”

Using these sensors as models, she and her team created a graphene-based electrochemical biosensor with an electrical readout set up to selectively detect the presence of SARS-CoV-2 genetic material.

Anatomy of a Biosensor

The new biosensor has two components--a platform to measure an electrical readout and probes to detect the presence of viral RNA. The platform is comprised of filter paper coated with a layer of graphene nanoplatelets to create a conductive film.  On top of the graphene, they placed a gold electrode with a predefined design, which acts as a contact pad for electrical readout.

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Currently, the RNA-based COVID-19 tests screen for the virus by detecting the presence of the N-gene (nucleocapsid phosphoprotein) on the SARS-CoV-2 virus. For the biosensor, researchers designed antisense oligonucleotide (ASO) probes to target two regions of the N-gene. By doing so, they aim to ensure the reliability of the senor in case one region undergoes gene mutation, researchers said.

The sensor also uses gold nanoparticles (AuNP) capped with single-stranded nucleic acids (ssDNA), which boosts sensing capability for the COVID-19 virus RNA, they added. Researchers published a paper on their work in the journal ACS Nano.

The team used COVID-19 positive and negative samples to test the performance of the sensor. The testing platform showed a significant increase in the voltage of positive samples compared to the negative ones, identifying the presence of viral genetic material in less than five minutes, researchers said.

Moreover, the sensor could also differentiate viral RNA loads in the samples it tested, which is a key indicator of how far the infection has progressed, they said. This has so far not been easy to measure using existing testing methods, researchers said.

The new testing platform also has other benefits for performing rapid COVID-19 tests, such as portability and low cost, Alafeef said. It also can be integrated with technology such as microcontrollers and LED screens or with a smartphone via Bluetooth or Wi-Fi, which means it can even be used to test for the virus at home, she added.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.