Advancing COVID‐19 Diagnosis: Enhancement in SERS‐PCR with 30‐nm Au Nanoparticle‐Internalized Nanodimpled Substrates

Real‐time polymerase chain reaction (RT‐PCR) with fluorescence detection is the gold standard for diagnosing coronavirus disease 2019 (COVID‐19) However, the fluorescence detection in RT‐PCR requires multiple amplification steps when the initial deoxyribonucleic acid (DNA) concentration is low. Therefore, this study has developed a highly sensitive surface‐enhanced Raman scattering‐based PCR (SERS‐PCR) assay platform using the gold nanoparticle (AuNP)‐internalized gold nanodimpled substrate (AuNDS) plasmonic platform. By comparing different sizes of AuNPs, it is observed that using 30 nm AuNPs improves the detection limit by approximately ten times compared to 70 nm AuNPs. Finite‐difference time‐domain (FDTD) simulations show that multiple hotspots are formed between AuNPs and the cavity surface and between AuNPs when 30 nm AuNPs are internalized in the cavity, generating a strong electric field. With this 30 nm AuNPs‐AuNDS SERS platform, the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) ribonucleic acid (RNA)‐dependent RNA polymerase (RdRp) can be detected in only six amplification cycles, significantly improving over the 25 cycles required for RT‐PCR. These findings pave the way for an amplification‐free molecular diagnostic system based on SERS.