A3G3 glycan (G3), procainamide labelled (A3G3 N-linked oligosaccharide, procainamide labelled; A3G(4)3 glycan, procainamide 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.