M6 glycan (Man6), 2-AB labelled (Mannose-6 N-linked oligosaccharide, 2-AB labelled; Oligomannose 6 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.