A core 1 / T antigen (Galβ1-3GalNAcα) presented on a serine residue and linked to 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. The Galβ1-3GalNAcα-O-Ser motif is the core 1 / T antigen, a tumor-associated carbohydrate antigen and ligand for galectins and the macrophage galactose lectin (MGL/CLEC10A). The serine presentation provides the natural mucin-type O-glycan context. The terminal Galβ residue is also a substrate for sialyltransferases (e.g., ST3Gal-I, ST6GalNAc to generate sialyl-T variants) and other glycosyltransferases, enabling enzymatic extension into more complex O-glycan structures. Used to build glycopeptides and probes for cancer immunology, mucin glycobiology, and lectin-binding research.