Chiral-Induced Surface-Enhanced Raman Optical Activity on Nanoparticle-On-Mirror Substrate

Raman Optical Activity (ROA) has emerged as a valuable tool for characterizing stereostructural changes in both organic and inorganic compounds, offering complementary steric information to traditional spectroscopic methods. In particular, ROA has garnered attention as a chiral-selective method for analyzing biomolecules such as nucleic acids, and peptides, overcoming the limitations of conventional spectroscopy. However, due to the inherently low cross-section of ROA, which is three to five orders of magnitude lower than typical Raman, achieving sufficient signal sensitivity remains a challenge. To address this issue, efforts have been made to measure ROA signals using SERS, which utilizes plasmonic materials to enhance the Raman signal of analytes via the electric field concentrated around nanoparticles (SEROA). However, biomolecules typically have low Raman cross-sections and poor signal stability at high laser intensity and long measuring times, limiting the utility of SEROA. Recently, chiral-induced ROA has been proposed as a breakthrough, leveraging the "sergeants-and-soldiers" principle to induce chirality in a trace chiral compound, enabling the measurement of chirality with shorter measuring times and lower laser intensities.<br/>This study demonstrates the possibility of a nanoparticle-on-mirror (NPoM) substrate and measurement configuration for ROA, which isolates hotspots from particle aggregation. To confirm the reliability of the NPoM configuration for ROA, chirality was induced in a self-assembled monolayer of 4-mercaptopyridine on a gold nanofilm surface.