The TE/TM polarized SER spectra obtained for 4MPy adsorbed on the AuAg NPs of the OCB are shown in Figure . Peak assignments for the SER spectra are based on previous studies where the Raman spectrum of 4MPy and its SER responses on different types of silver substrates were examined . Raman peaks at 1061, 1191, and 1227 cm -1 belong respectively to the 18b2 β(CH), 9a1 β(CH), and 3b2 β(CH) in-plane bending modes of the pyridine ring. The peaks at 1587 and 1617 cm -1 originate in 8b2 and 8a1 νCC pyridine carbon stretching modes. The absence of a peak for (SH) is attributed to the X-sensitive vibrations of 4MPy, which are mixed modes that result from the coupling of the 1a1 ring breathing mode with the vibration of the substituent (sulfur) of pyridine in the 4-position . With this reasoning, the 1a1 ring breathing mode at 1011 cm -1 is coupled with the 12a1 species at 1094 cm -1 , which is the most intense feature in this spectrum region, indicating the sulfur substituent moves with significant amplitude when bound to Ag/Au.