A One-Second Saliva-Based COVID Test

By Sam Brusco, Associate Editor | 06.02.21

Researchers have built a microfluidic device capable of detecting the SARS-CoV-2 spike protein in a saliva sample within an astonishing one second.

Detecting the SARS-CoV-2 virus may soon be as quick as snapping your fingers.

The pandemic made it quite clear that technological advances were necessary to spot, treat, and prevent the virus. A year and a half later, waves of successive outbreaks and dire need for new medical solutions—particularly in testing—continue to exist.

Schematic and photograph of COVID-19 sensor strip and the printed circuit board fabricated to produce a digital sensor output. Image courtesy of AIP Publishing.
Researchers from the University of Florida and the National Chiao Tung University in Taiwan have built a microfluidic device capable of detecting the SARS-CoV-2 spike protein in a saliva sample within an astonishing one second. The electrochemical device uses antibodies against the spike protein to spot the virus, and could allow for ultra-rapid COVID-19 testing.

Aside from collection via conventional oropharyngeal swabs, SARS-CoV-2 has been spotted in saliva, indicating it may contribute as a transmission route. However, this also means there exists an opportunity for virus testing using a simple, noninvasive collection method.

The current standard, Abbott’s BinaxNOW rapid antigen COVID-19 test, takes five minutes to confirm an infection.

“This could alleviate slow COVID-19 testing turnaround time issues,” Minghan Xian, an author and a chemical engineering doctoral candidate at the University of Florida, told the press.

The researchers have previously demonstrated biomarker detection relevant for epidemics and emergencies like the Zika virus, heart attacks, and cerebral spinal fluid leaks. These accomplishments helped leverage their expertise to develop a sensor system that detects biomarkers in one second.

Viral detection takes place on a gold electrode lined with antibodies against the viral spike protein, which is then loaded with the saliva sample. When the spike protein binds to the electrode, the electrical charge running through it changes to spot the virus.

Spotting the virus’s presence requires amplifying the numbers of the copies of viral ribonucleic acid in the common polymerase chain reaction (PCR) for COVID-19 detection, or amplifying the target biomarker’s binding signal. The researchers’ method amplifies the binding signal for a target biomarker.

“Our biosensor strip is similar to commercially available glucose test strips in shape, with a small microfluidic channel at the tip to introduce our test fluid,” said Xian. “Within the microfluidic channel, a few electrodes are exposed to fluid. One is coated with gold, and COVID-relevant antibodies are attached to the gold surface via a chemical method.”

During measurement, sensor strips are connected to the circuit board with an embedded metal-oxide-semiconductor field-effect transistor (MOSFET) via a connector. A short electrical test signal is sent between the gold electrode bonded with the COVID-19 antibody and another auxiliary electrode. This signal is then returned to the circuit board for analysis.

“Our sensor system, a circuit board, uses a transistor to amplify the electrical signal, which then gets converted into a number on the screen,” said Xian. “The magnitude of this number depends on the concentration of antigen, the viral protein, present within our test solution.”

The system’s biosensor strips have to be discarded after use, but the test printed circuit board is reusable. This could mean greatly reduced costs for testing, and this technology’s versatility extends way beyond detecting COVID-19. The portable and inexpensive cartridge sensor described opens the door for off-site biomarker testing of viral and life-threatening diseases with fast turnaround time.

“By altering the type of antibodies attached to the gold surface, we can repurpose the system to detect other diseases,” said Xian. “The system can serve as a prototype for modularized, inexpensive protein biomarker sensors for expedient real-time feedback within clinical applications, operating rooms, or home use.”