Aqueous solutions of 1 mM of 2,3 sialyllactose (3-SLA), 1 mM of 2,6 sialyllactose (6-SLA), and an equal volume mixture of sialic acid (0.5 mM) and lactose (0.5 mM) were prepared to represent α2,3 sialic linkage, α2,6 sialic acid linkage, and no linkage between sialic acid and other glycans, respectively. The samples were spotted on the BA-coated nanopapers and incubated at room temperature for 1 hour. Afterward, the nanopaper was then dried in an oven at 75℃ for 5 minutes and measured by Raman spectrometer using the same protocol reported above, with 200 spectra collected for each concentration.