Microfluidic immunoassay for detection of serological antibodies: A potential tool for rapid evaluation of immunity against SARS-CoV-2

In December 2019, coronavirus disease 2019 became a pandemic affecting more than 200 countries and territories. Millions of lives are still affected because of mandatory quarantines, which hamstring economies and induce panic. Immunology plays a major role in the modern field of medicine, especially against virulent infectious diseases. In this field, neutralizing antibodies are heavily studied because they reflect the level of infection and individuals' immune status, which are essential when considering resumption of work, flight travel, and border entry control. More importantly, it also allows evaluating the antiviral vaccine efficacy as vaccines are still known for being the ultimate intervention method to inhibit the rapid spread of virulent infectious diseases. In this Review, we first introduce the host immune response after the infection of SARS-CoV-2 and discuss the latest results using conventional immunoassays. Next, as an enabling platform for detection with sufficient sensitivity while saving analysis time and sample size, the progress of microfluidic-based immunoassays is discussed and compared based on surface modification, microfluidic kinetics, signal output, signal amplification, sample matrix, and the detection of anti-SARS-CoV-2 antibodies. Based on the overall comparison, this Review concludes by proposing the future integration of visual quantitative signals on microfluidic devices as a more suitable approach for general use and large-scale surveillance.