A2G2S2 glycan (G2S2), 2-AB labelled (A2G2S2 N-linked oligosaccharide, 2-AB labelled; A2G(4)2S(6)2 glycan, 2-AB labelled) is a N-polysaccharide protein and a multifunctional fluorescent linker. The resulting conjugates exhibit high sensitivity and specificity by mimicking the antennal elements of N-glycans.