Rapid and simultaneous detection of SARS-CoV-2 and influenza A using vertical flow assay based on AAO and SERS nanotags

The clinical symptoms of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are similar to those of influenza A infection. Therefore, accurate diagnosis of SARS-CoV-2 and influenza A in the early infection stage is essential for appropriate clinical treatment. In this work, a vertical flow assay (VFA) device based on Au@Ag@Au core–shell SERS nanotags and anodic aluminum oxide (AAO) was proposed to diagnose and distinguish between SARS-CoV-2 and influenza A at the same time. Antibodies paired with SARS-CoV-2 and influenza A were immobilized simultaneously on the AAO. In the presence of SARS-CoV-2 or influenza A antigens, sandwich immune-complexes were formed on the AAO and the corresponding SERS signals of nanotags could be detected. The whole detection process took only about 15 minutes, taking comparable or even shorter time than reported POCT antigen assays. The detection limit reached 0.47 pg ml−1 for SARS-CoV-2 nucleocapsid protein (NP) and 0.62 pg ml−1 for influenza A antigen. The clinical feasibility of the proposed VFA device was validated by testing clinical throat swab samples (3 SARS-CoV-2 positive samples and 17 negative samples). Real sample analysis indicated a well-distinguished positive/negative sample group. Conceptually, this VFA device is a potential POCT diagnosis tool for determining if a suspected patient is infected with SARS-CoV-2 or influenza A.