A reagent for conjugation to a biomolecule, wherein the reagent is a single molecule with at least three functional parts and has schematic structure (I): a) wherein a trifunctional cross-linking moiety is coupled to b) an affinity ligand via a linker 1, said affinity ligand being capable of binding with another molecule having affinity for said ligand, to c) an effector agent, optionally via a linker 2, said effector agent exerting its effect on cells, tissues and/or humorous molecules in vivo or ex vivo, and to d) a biomolecule reactive moiety, optionally via a linker 3, said moiety being capable of forming a bond between the reagent and the biomolecule.
