Diagnostic devices used at home or in doctors’ offices are often not sensitive enough to detect small amounts of the virus that may be present in samples from asymptomatic patients, which can occur during the early stages of COVID-19. Scientists are reporting a membrane-based invention that can concentrate the viral content of a urine or saliva sample, making it easier to detect. The research results are published by the specialized journal Biomicrofluidics.
To increase the concentration of the sample, previous teams of scientists used gel particles bound with a chemical dye to capture and detect the virus. However, this approach is limited to the specific viruses that can bind to the dye. In addition, testing time can be over 30 minutes and requires expensive equipment.
Of course, scientists have tried other approaches, but they all lack the ability to diagnose various viruses or other biological substances of interest, such as human chorionic gonadotropin (hCG), a hormone present in urine during pregnancy.
Researchers at the University of Cincinnati and Wright-Patterson Air Force Base tried two different devices based on similar membrane filter systems.
The first device was a fully integrated concentration unit along with a component that could detect the virus in question. Using a vacuum, water was passed through the membrane, leaving the virus in a more concentrated solution, and the sample was analyzed on the same device.
“The time it took to complete the concentration process was very slow,” said author Amy Drexelius. “On average, each device took about 30 minutes to complete the concentrating process. Therefore, we concluded that the automatic step device with a vacuum drive was practically useless and turned to an alternative device using much higher positive pressure. ”
The researchers realized that by applying high pressure instead of high vacuum, they could increase the pressure drop between the sample and the environment. Attached to their second device was a nitrogen cylinder and a regulator that could generate pressures up to 45 kg per square inch (6.4 cm).
The team examined samples of saliva and urine, with added protein samples from the influenza A virus. Other samples contained hCG.
The test results completely matched the second device, showing a concentration result 33 times higher than that of the original sample, the scientists say. The concentration of a 1 ml sample can be achieved in five minutes or faster with higher applied pressure.
The new coronavirus that causes COVID-19 has not been tested, but this method should work for it, as the technology can successfully detect influenza A. Both respiratory viruses are likely present in saliva. In addition, this method holds promise for pregnancy testing where early results are also highly desirable.