Alfredo Ongaro prepares the device in the Optoelectronics lab to take to the Biology lab at ICFO for testing of the saliva samples. (Credit: ICFO)

A new low-cost portable instrument manipulates light and fluid for fast and reliable detection of SARS-CoV-2 in saliva samples. Although still in the research stage, the new device could offer a higher sensitivity than today’s COVID-19 rapid antigen tests while also being faster and more cost-effective than PCR tests.

The researchers report that the system correctly detected 91.2 percent of COVID-19 positive cases and 90 percent of negative cases in tests of more than 50 previously frozen saliva samples. The test can measure very small quantities of virus like PCR tests but is as fast as rapid antigen tests.

The new instrument, which the researchers call a flow virometry reader, is based on a modification of flow cytometry, a laser-based technique that uses fluorescence to count or analyze cells. Rather than counting cells, the new device detects light emission from fluorescent antibodies that bind to specific viral particles. It can offer quantitative results in less than 30 minutes using an instrument that is about the size of a shoebox.

To run a test, a saliva sample is introduced in a solution that contains fluorescent antibodies that will attach to SARS-CoV-2 particles. The sample is then processed by the flow virometry reader, which uses a single microfluidic channel to pass the sample through a laser illumination and detection setup. If viral particles are present in the solution, they change the sample’s fluorescence in a detectable way, providing information that can be used to calculate the viral concentration.

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