A GlcNAcβ1-3-capped di-LacNAc ligand equipped with a terminal carboxylic acid through a hydrophilic PEG3 spacer. The carboxylic acid can be activated to NHS, sulfo-NHS, or pentafluorophenyl esters and reacted with amine-functionalized platforms or lysine residues on proteins and peptides to form amide bonds. This compound presents extended poly-N-acetyllactosamine (poly-LacNAc) chains, which are high-affinity galectin ligands and substrates for sialyltransferases and fucosyltransferases, used to build glycoconjugates and probes for galectin and lectin research.