Microfluidic immunoassay for the detection of SARS-CoV-2 neutralizing antibodies in ultralow-volume human plasma samples

• Microfluidic immunoassay for ultralow-volume plasma samples • Rapid on-site neutralizing antibody testing • Parallel channel design for simultaneous analysis and validation Infectious disease outbreaks are not only a globally recognized threat to human health, they can also put a significant strain on any country's healthcare system. Consequently, effective immunization strategies, including the maintenance of the immune protection within a population, are crucial to either prevent disease outbreaks or limit their severity. However, due to the inherent variability between individuals, it is often unclear how long immunity lasts. By assessing the presence of neutralizing antibodies, vaccination efficacy and, ultimately, an individual's immune response can be determined. However, to gain a deeper understanding of the correlation between antibody titer and disease severity, large-scale testing regimes need to be implemented to truly predict vaccine efficiencies. To make neutralizing antibody testing broadly accessible, we developed an easy-to-use microfluidic fluorescent beads immunoassay, capable of detecting neutralizing antibodies within 30 minutes with a detection limit of 46 IU/mL. As a practical example, neutralizing antibodies against SARS-CoV-2 of human plasma samples were analyzed, requiring a maximum sample volume of 1.35 µL. This was accomplished by developing a fluorescent beads immunoassay that detects primarily the inhibition of binding events between trimeric spike proteins of the virus envelope and angiotensin-converting enzyme 2 cell surface receptor in the presence of neutralizing antibodies. By emulating the virus-host interaction on this novel biochip platform it is possible to assess the efficacy of neutralizing antibodies against SARS-CoV-2 infections, thus providing insight into an individual's protective status.