Probing the\nLocal Field Enhancement Using SERS Detection\nof DNA Strands with Different Lengths and Grafting Strategies on Graphene\nOxide Plasmonic Nanoplatforms

Surface-enhanced Raman spectroscopy (SERS) has emerged\nas a powerful\ntool for analyzing nucleic acids due to its exceptional sensitivity\nand specificity. This study rigorously investigates not only the impact\nof polyA strands of different lengths (<i>i.e.</i>, 5, 10,\n15, and 20 adenine bases) but also their distinct grafting strategy\n(SH at 5′ and NH<sub>2</sub> at 5′ end) on the SERS\nsignal of DNA strand using <i>in situ</i> synthesized gold\nnanoparticles (AuNPs) on graphene oxide sheets (GO-AuNPs). By comparing\nthe thiol vs amine bonding onto the GO-AuNP nanoplatform, we found\na strong correlation between the adenine peak intensity at 732 cm<sup>–1</sup> and the strand length for both grafting methods (SH\nat 5′ end or NH<sub>2</sub> at 5′ end). We demonstrated\nthat these intensity variations are highly influenced by the electromagnetic\nfields from the metallic surface proximity or in between SERS hot-spots\nformed by the AuNP dimer, as confirmed by numerical simulations. Such\nresults have allowed us to probe the local field enhancement generated\nby individual AuNPs or dimers and its decay length.