Next-Generation Rapid and Ultrasensitive Lateral Flow Immunoassay for Detection of SARS-CoV-2 Variants

The coronavirus disease 2019 (COVID-19) pandemic highlighted the need for rapid and accurate viral detection at the point-of-care testing (POCT). Compared with nucleic acid detection, lateral flow immunoassay (LFIA) is a rapid and flexible method for POCT detection. However, the sensitivity of LFIA limits its use for early identification of patients with COVID-19. Here, an innovative surface-enhanced Raman scattering (SERS)-LFIA platform based on two-dimensional black phosphorus decorated with Ag nanoparticles as important antigen-capturing and Raman-signal-amplification unit was developed for detection of SARS-CoV-2 variants within 5-20 min. The novel SERS-LFIA platform realized a limit of detection of 0.5 pg/mL and 100 copies/mL for N protein and SARS-CoV-2, demonstrating 1000 times more sensitivity than the commercial LFIA strips. It could reliably detect seven different SARS-CoV-2 variants with cycle threshold (Ct) < 38, with sensitivity and specificity of 97 and 100%, respectively, exhibiting the same sensitivity with q-PCR. Furthermore, the detection results for 48 SARS-CoV-2-positive nasopharyngeal swabs (Ct = 19.8-38.95) and 96 negative nasopharyngeal swabs proved the reliability of the strips in clinical application. The method also had good specificity in double-blind experiments involving several other coronaviruses, respiratory viruses, and respiratory medications. The results showed that the innovative SERS-LFIA platform is expected to be the next-generation antigen detection technology. The inexpensive amplification-free assay combines the advantages of rapid low-cost POCT and highly sensitive nucleic acid detection, and it is suitable for rapid detection of SARS-CoV-2 variants and other pathogens. Thus, it could replace existing antigens and nucleic acids to some extent.