Impact of adsorbed molecules on the relative intensity of surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) enhances molecules' vibrational signals for single-molecule detection which correlates with light-induced polarizability variations. The involved charge-transfer process impacts molecular polarizability, offering efficient modulation methods for SERS. Herein, the effect of ambient molecules (H₂O, CO₂, and N₂) on the SERS spectra of a metal-pyridine (Py) system is explored. It is found that the relative intensity changes differently between vibrational modes when adsorbing different ambient molecules. Especially, CO₂ adsorption alters the intensity ratios between ring-breathing and ring-stretching modes in Py molecule. Further polarizability analysis shows that CO₂'s larger polarizability contribution and adsorption configuration lead to the dominating ring-breathing mode. Additionally, SERS enhancement reduces with increasing ambient molecules, due to weakened electron exchange between Py and metal substrate. This study has the potential to provide an insight into detecting relative intensity changes in SERS and promote the development of related applications. © 2025 American Physical Society.