Single-Nanoparticle-Based Digital SERS Sensing Platform for the Accurate Quantitative Detection of SARS-CoV-2

To prevent the ongoing spread of the highly infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), accurate and early detection based on a rapid, ultrasensitive, and highly reliable sensing method is crucially important. Here, we present a bumpy core-shell surface-enhanced Raman spectroscopy (SERS) nanoprobe-based sensing platform with single-nanoparticle (SNP)-based digital SERS analysis. The tailorable bumpy core-shell SERS nanoprobe with an internal self-assembled monolayer of 4-nitrobenzenethiol Raman reporters, synthesized using HEPES biological buffer, generates a strong, uniform, and reproducible SERS signal with an SNP-level sensitive and narrowly distributed enhancement factor (2.1 × 10⁸ to 2.2 × 10⁹). We also propose an SNP-based digital SERS analysis method that provides direct visualization of SNP detection at ultralow concentrations and reliable quantification over a wide range of concentrations. The bumpy core-shell SERS nanoprobe-based sensing platform with SNP-based digital SERS analysis achieves the ultrasensitive and quantitative detection of the SARS-CoV-2 spike protein with a limit of detection of 7.1 × 10^-16 M over a wide dynamic range from 3.7 × 10^-15 to 3.7 × 10^-8 M, far outperforming the conventional enzyme-linked immunosorbent assay method for the target protein. Furthermore, it can detect mutated spike proteins from the SARS-CoV-2 variants, representing the key mutations of Alpha, Beta, Gamma, Delta, and Omicron variants. Therefore, this sensing platform can be effectively and efficiently used for the accurate and early detection of SARS-CoV-2 and be adapted for the ultrasensitive and reliable detection of other highly infectious diseases.