Probing the Local Field Enhancement Using SERS Detection of DNA Strands with Different Lengths and Grafting Strategies on Graphene Oxide Plasmonic Nanoplatforms

Surface-enhanced Raman spectroscopy (SERS) has emerged as a powerful tool for analyzing nucleic acids due to its exceptional sensitivity and specificity. This study rigorously investigates not only the impact of polyA strands of different lengths (<i>i.e.</i>, 5, 10, 15, and 20 adenine bases) but also their distinct grafting strategy (SH at 5' and NH₂ at 5' end) on the SERS signal of DNA strand using <i>in situ</i> synthesized gold nanoparticles (AuNPs) on graphene oxide sheets (GO-AuNPs). By comparing the thiol vs amine bonding onto the GO-AuNP nanoplatform, we found a strong correlation between the adenine peak intensity at 732 cm^-1 and the strand length for both grafting methods (SH at 5' end or NH₂ at 5' end). We demonstrated that these intensity variations are highly influenced by the electromagnetic fields from the metallic surface proximity or in between SERS hot-spots formed by the AuNP dimer, as confirmed by numerical simulations. Such results have allowed us to probe the local field enhancement generated by individual AuNPs or dimers and its decay length.