Because SERS is a near-field effect, we hypothesize that the major Raman signals are contributed by BA-glycan reaction complexes that directly attach to SERS substrates. To verify the hypothesis, we compared the SERS spectra of extracted oligosaccharides and unprocessed milk samples on 4MBA functionalized substrates (Cow milk example shown in Figure & a detailed comparisons among other milk samples in SI Figure ). Milk was dropped onto a surface-modified nanopaper, and then the nanopaper was rinsed with the buffer to remove unbound proteins and non-glycan contents. The spectral difference between processed and unprocessed milk samples is minimal. The small spectral differences were observed at 470 cm -1 (CCC out of plane bending), 607 cm -1 (CCC inplane bending), 1075 cm -1 (CCC in-plane bending, CS stretching), and 1589 cm -1 (CC stretching, CH bending). Since the milk oligosaccharides were extracted using Folch method, lipids and proteins were removed during the separation process