Controlled nanogap formation in electrochemical SERS gold nanosubstrates: Enhancing sensitivity through Au nano-popcorn structures

Abstract

This study presents a novel approach to enhance the sensitivity of surface-enhanced Raman scattering (SERS)-based DNA hybridization assays using electrochemical SERS (EC-SERS) on gold nano-popcorn substrates (AuNPSs). While polymerase chain reaction (PCR) remains the gold standard for molecular diagnostics, it has time and labor intensity limitations. SERS spectroscopy offers advantages in sensitivity, speed, and potential for point-of-care testing. Building on previous work with gold nano-dimple substrates, we developed a platform utilizing AuNPSs, which exhibit higher SERS enhancement factors. We achieved significant improvements in sensitivity by applying an electric potential to control the nanogap between the AuNPSs and DNA-SERS nanotags. The RNA-dependent RNA polymerase (RdRp) genes of SARS-CoV-2 were used as a target marker model. The electrically controlled nanogap flattens the DNA hybridization complex, bringing the malachite green Raman reporter closer to the AuNPS surface. This approach improved the detection limit by up to 10 times that of conventional SERS-based DNA hybridization assays. We also optimized hybridization conditions and performed an EC-SERS analysis. This novel EC-SERS platform represents a significant step towards developing amplification-free molecular diagnostics with enhanced sensitivity and rapid detection capabilities. The technology shows promise for application in various fields requiring sensitive and specific molecular diagnostics.