SERS-PCR assays of SARS-CoV-2 target genes using Au nanoparticles-internalized Au nanodimple substrates

The reverse transcription-polymerase chain reaction (RT-PCR) method has been adopted worldwide to diagnose severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although this method has good sensitivity and specificity, there is a need to develop a more rapid diagnostic technology, given the virus's rapid spread. However, the RT-PCR method takes a long time to diagnose SARS-CoV-2 because of the required thermocycling steps. Therefore, we developed a surface-enhanced Raman scattering (SERS)-PCR detection method using an AuNP-internalized Au nanodimple substrate (AuNDS) to shorten the diagnosis time by reducing the number of thermocycling steps needed to amplify the DNA. For the representative target markers, namely, the envelope protein (E) and RNA-dependent RNA polymerase (RdRp) genes of SARS-CoV-2, 25 RT-PCR thermocycles are required to reach a detectable threshold value, while 15 cycles are needed for magnetic bead-based SERS-PCR when the initial DNA concentration was 1.00× 10⁵ copies/μL. However, only 8 cycles are needed for the AuNDS-based SERS-PCR. The corresponding detectable target DNA concentrations were 3.36 × 10¹², 3.28 × 10⁹, and 2.56 × 10⁷ copies/μL, respectively. Therefore, AuNDS-based SERS-PCR is seen as being a new molecular diagnostic platform that can shorten the time required for the thermocycling steps relative to the conventional RT-PCR.