Rapid, Point-of-Care scFv-SERS Assay for Femtogram Level Detection of SARS-CoV-2

Rapid, sensitive, on-site identification of SARS-CoV-2 infections is animportant tool in the control and management of COVID-19. We have developed asurface-enhanced Raman scattering (SERS) immunoassay for highly sensitive detection ofSARS-CoV-2. Single-chain Fv (scFv) recombinant antibody fragments that bind theSARS-CoV-2 spike protein were isolated by biopanning a human scFv library. ScFvs wereconjugated to magnetic nanoparticles and SERS nanotags, followed by immunocomplexformation and detection of the SARS-CoV-2 spike protein with a limit of detection of 257fg/mL in 30 min in viral transport medium. The assay also detected B.1.1.7 (alpha),B.1.351 (beta), and B.1.617.2 (delta) spike proteins, while no cross-reactivity wasobserved with the common human coronavirus HKU1 spike protein. Inactivated wholeSARS-CoV-2 virus was detected at 4.1x104genomes/mL, which was 10-100-fold lowerthan virus loads typical of infectious individuals. The assay exhibited higher sensitivity forSARS-CoV-2 than commercial lateralflow assays, was compatible with viral transportmedia and saliva, enabled rapid pivoting to detect new virus variants, and facilitated highly sensitive, point-of-care diagnosis ofCOVID-19 in clinical and public health settings.

Automated summary

The authors developed a surface-enhanced Raman scattering (SERS) immunoassay for highly sensitive detection of SARS-CoV-2. This assay exhibited higher sensitivity than commercial lateral flow assays, detected different spike protein variants, and enabled rapid on-site diagnosis of COVID-19 in clinical and public health settings.