Scientists have developed a stamp-sized chip that simplifies COVID-19 testing, and delivers results on a smartphone in less than 55 minutes. The microfluidic chip developed by researchers from Rice University in the US measures the concentration of SARS-CoV-2 nucleocapsid (N) protein, a biomarker for COVID-19, in blood serum from a standard finger prick.
According to the research published in the journal ACS Sensors, the nanobeads bind to SARS-CoV-2 N protein in the chip and transport it to an electrochemical sensor that detects minute amounts of the biomarker. The researchers noted that their process simplifies sample handling compared to swab-based PCR tests that are widely used to diagnose COVID-19 and need to be analysed in a laboratory.
"What's great about this device is that it doesn't require a laboratory," said Rice lab of mechanical engineer Peter Lillehoj. "You can perform the entire test and generate the results at the collection site, health clinic or even a pharmacy. The entire system is easily transportable and easy to use," he said in a statement. The team, including Rice graduate student and lead author Jiran Li, took advantage of existing biosensing tools to develop simple diagnostics, like a microneedle patch introduced last year to diagnose malaria.
The new tool relies on a slightly more complex detection scheme but delivers accurate, quantitative results in a short amount of time. To test the device, the researchers relied on donated serum samples from people who were healthy and others who were COVID-19-positive. They said a longer incubation yields more accurate results when using whole serum. The team found that 55 minutes was an optimum amount of time for the microchip to sense SARS-CoV-2 N protein at concentrations as low as 50 picograms (billionths of a gram) per millilitre in whole serum.
The microchip could detect N protein in even lower concentrations, at 10 picograms per milliliter, in only 25 minutes by diluting the serum fivefold. Paired with a Google Pixel 2 phone and a plug-in potentiostat -- a device that controls voltage and measures resulting current -- it was able to deliver a positive diagnosis with a concentration as low as 230 picograms for whole serum. "There are standard procedures to modify the beads with an antibody that targets a particular biomarker," Lillehoj said.
"When you combine them with a sample containing the biomarker, in this case SARS-CoV-2 N protein, they bond together," he added. A capillary tube is used to deliver the sample to the chip, which is then placed on a magnet that pulls the beads towards an electrochemical sensor coated with capture antibodies. The beads bind to the capture antibodies and generate a current proportional to the concentration of biomarker in the sample. The potentiostat reads that current and sends a signal to its phone app. If there are no COVID-19 biomarkers, the beads do not bind to the sensor and get washed away inside the chip.
