Figure displays normalized SERS spectra of fetuin and asialofetuin binding to 4MBA, and the spectra of 1TBA, 3MBA, 4ABA, and PyriBA are shown in SI Figure . For 4MBA spectra, sialic acid residues in fetuin cause the peak shifts to higher wavenumber and the increases of intensity at 475 cm -1 (CCC out of plane bending) and 613 cm -1 (CCC in plane bending). Similarly, the presence of sialic acid residues also results in the variations of signal intensities at 1015 cm -1 (CC stretching, OH stretching) and at 1589 cm -1 (CC stretching, CH bending). These spectral changes are consistent with the data of sialic acid monosaccharide observed in our prior study . For 1TBA, the spectra differences among fetuin, asialofetuin, and negative control (no glycoprotein) are more significant. With sialic acid residue, the lower spectral signals were observed at 431 cm -1 (CCCC torsion, SCCC out-of-plane bending), 669 cm -1 (CCCC torsion, CCC in-plane bending), 1037 cm -1 (CC stretching), 1125 cm -1 (CC stretching, HCC bending), and 1194 cm -1 (CC stretching). In contrast, the signals raise at 1081 cm -1 (CC stretching) and 1554 cm -1 (CC stretching) when sialic acid residues present. This changes are consistent with our prior observations of sialic acid .