Figure shows the TE/TM SER spectra of 4ABA molecules bound to AuAg NPs on the OCB. The unenhanced Raman spectrum of crystalline 4ABA is provided in Figure for comparison. The most prominent TE polarization peaks in the 4ABA SERS occur at 1126, 1386, and 1603 cm -1 , attributed to NH2 bending (τNH2), COO -stretching (νCOO -), and NH2 deformation (δNH2), respectively . In the Raman spectrum of crystalline 4ABA (Figure ), the τNH2 mode is weak while the νC-OH mode appears as a peak of medium strength at 1293 cm -1 . The SERS of Figure shows a significant enhancement in the τNH2 mode and a blue-shift and moderate enhancement of the COO -stretching mode, suggesting that both the amine and carboxylic acid groups of 4ABA are involved in binding to the AuAg NPs. Previous studies indicated that 4ABA can bind through both amino and carboxylic acid groups . In terms of binding modes, the monocarboxylic acid was shown to bind through both oxygen atoms to two adjacent atoms in a symmetric -bridging fashion on the surface of Ag/Au , while amino acids bind to metal surfaces by donating the nitrogen lone pair to the antibonding orbitals of the metal, or by accepting the lone pair electrons of metal to the antibonding orbitals of N-H bonds . The strong peak at 1603 cm -1 is assigned as an overlap of ν8a ring stretching vibration and δNH2 deformation. In crystalline 4ABA, the ν8a band shows the strongest intensity among all Raman modes, while the δNH2 band has a much weaker intensity and often appears as a shoulder to the ν8a peak. Similar to the τNH2 mode, the intensity of the δNH2 mode is greatly enhanced upon metal binding. Past research has shown that the δNH2 band gets strongly enhanced due to interaction with the silver surface, surpassing the ν8a band in intensity .