Nanofluidic Device for Detecting SARS-CoV-2 Antibodies

Point-of-care tests for the fast diagnosis of viral diseases can help to avoid further transmission. The SARS-CoV-2 pandemic has demonstrated the importance of such techniques. The state of the art for immunoassays in laboratory tests is the use of enzyme-linked immunosorbent assay (ELISA) methods. They can give quantitative results for anti-SARS-CoV-2 antibody levels, but are time-consuming. Fast, easy-to-use, low-cost lateral flow tests do not have this problem, but have limited sensitivities.

Yasin Ekinci, Paul Scherrer Institute, Villigen, Switzerland, and colleagues have developed a nanofluidic device that can be used for the rapid detection of antibodies against multiple viruses at the same time, e.g., SARS-CoV-2 and influenza A. The team used grayscale electron beam lithography and nanoimprint lithography to crate a nanostructured poly(methyl methacrylate) (PMMA) device. Liquid can move through the device using capillary force, and no external pump is required. The device acts as nanofluidic particle sorter, trapping different particles at different positions in narrowing channels.

This sorting mechanism can be used for assays to detect antibodies. The team functionalized tiny polymer beads with SARS-CoV-2 spike protein domains and mixed them with human serum samples. If SARS-CoV-2 antibodies are present, they bind to the spike proteins, and thus, to the beads. The antibody-decorated beads are then trapped at a specific location in the nanofluidic device depending on their size. Fluorescence measurements are used to detect the trapped particles. The test showed high sensitivity and specificity.

The researchers also functionalized a second set of polymer beads with a different antigen (in this case, influenza hemagglutinin) and mixed them with the beads decorated with SARS-CoV-2 spike protein domains. This allowed the team to simultaneously detect SARS-CoV-2 and influenza A antibodies, because the resulting particles have different sizes and are trapped at different positions in the nanofluidic device.