A sialyl-Tn antigen (Neu5Acα2-6GalNAcα) on a serine residue equipped with a biotin tag through an amide bond. The biotin moiety binds with high affinity to streptavidin and neutravidin, enabling straightforward immobilization on chips, in wells, or on other streptavidin/neutravidin-coated platforms. This compound presents the sialyl-Tn antigen (Neu5Acα2-6GalNAcα) on a serine residue, a tumor-associated carbohydrate antigen and ligand for Siglecs and anti-STn antibodies relevant to cancer immunology. The biotin tag enables immobilization on streptavidin/neutravidin-coated platforms.