SERS-based lateral flow immunoassay for rapid and sensitive sensing of nucleocapsid protein toward SARS-CoV-2 screening in clinical samples.

Early and accurate identification of SARS-CoV-2 infection is crucial for epidemic prevention and control. Lateral flow immunoassay (LFIA) has become the mainstream method for screening SARS-CoV-2 infection due to its rapid, simple and amenable for point-of-care detection (POCT), but still suffered from the poor sensitivity and accuracy. In this study, Au nanoparticles (NPs) with controllable Ag shell (Au@Ag) were manufactured via a seed-mediated growth method. The Au@Ag-based LFIA exhibited superb colorimetric (CM) signal and intense surface-enhanced Raman scattering (SERS) signal for dual-mode sensing of nucleocapsid protein (N protein), a naturally protein expression in vivo during SARS-CoV-2 infection. The limit of detection (LOD) of the SERS-LFIA mode was 2.16 pg/mL, which was around 150-time more sensitive than conventional visual CM-LFIA mode (300 pg/mL). More importantly, the proposed LFIA is capable of quantitatively detecting N protein-spiked real samples with satisfactory recoveries from 83 % to 91.4 %. Clinical pharyngeal swab samples of the infected patients (n = 20) and healthy subjects (n = 20) were effectively discriminated in the developed SERS-LFIA, where the negative accuracy rate was 100 % and the positive accuracy rate was 85 %, among which samples from P1, P18, and P19 were false-negative results. The results obtained from the LFIA immunoassay were in good agreement with the standard PCR method in clinic, and superior to those of the commercially colloidal gold strip by using the same antibodies. In conclusion, the LFIA proposed here can perform specific, rapid, and ultrasensitive analysis of N protein toward early warning of SARS-CoV-2 infection.