A2G2S2 glycan (G2S2), APTS labelled (A2G2S2 N-linked oligosaccharide, APTS labelled; A2G(4)2S(6)2 glycan, APTS 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.