The continuing global spread of Coronavirus Disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection, has led to an unprecedented global health crisis. Effective and affordable methods are needed to diagnose SARS-CoV-2 infection. In this work, a ratiometric fluorescence probe, Si-Mn:ZnSe nanoparticles, was constructed through the electrostatic interaction between Si dots and Mn:ZnSe QDs, and the fluorescence of Mn:ZnSe QDs has a specifical response to H₂O₂. An immunocomplex was formed by the recognition of capture antibody/spike (S) protein/spike neutralizing antibody/biotinylated second antibody/streptavidin/biotinylated catalase (CAT). In the presence of S protein, CAT effectively catalyzed the decomposition of H₂O₂ in the system, and the fluorescence of Mn:ZnSe QDs was not specifically quenched. Based on this principle, a ratiometric immunoassay of SARS-CoV-2 S protein was established. The sensitivity of the proposed ELISA method was comparable to that of the commercial kit. In addition, this method can effectively distinguish the pseudo-SARS-CoV-2 virus and other pseudovirus. Therefore, this method provided a reliable and potential direction for diagnosing SARS-CoV-2 infection.

Influenza A viruses (IAVs) are significant respiratory pathogens characterized by high mutation rates and frequent genetic reassortments, underscoring the need for vaccines that can induce robust and broadly protective mucosal immunity. While replication-competent vesicular stomatitis virus (VSV) vectors have the potential to elicit mucosal immunity, their neurovirulence raises significant safety concerns. Herein, we report that a semi-replicating VSV (srVSV) vector, composed of one VSV with the glycoprotein (G) gene deleted (rVSVΔG) and another with the L gene deleted (rVSVΔL), has improved safety. Using srVSV, we constructed a monovalent vaccine (srVSV-N1), expressing the neuraminidase 1 (N1) of IAV. A single intranasal dose of srVSV-N1 elicited both systemic and mucosal immune responses against N1, and provided sterilizing immunity against homologous influenza virus. We further generated a bivalent IAV vaccine (srVSV-N1/N2), co-expressing N1 and N2. A single intranasal dose of srVSV-N1/N2 conferred 80% protection against heterologous IAVs (H1N1 and H3N2). Notably, low-dose priming immunization followed by a high-dose boost with srVSV-N1/N2 fully protected mice against lethal heterologous IAV challenges. These findings demonstrate the potential of the srVSV platform for developing mucosal vaccines against IAVs and other respiratory viruses.