Described herein is a modification unit (37) for the continuous, germ-reduced processing of a guidance molecule and a linker comprising the following components: - at least one reservoir containing the guidance molecule in buffer solution (1) and/or at least one inlet for a product stream containing the guidance molecule in buffer solution, - at least one reservoir containing the linker in solution (2), - at least one mixing device (3), - at least two valves (7, 8), one for dosage of the guidance molecule and one for dosage of the linker molecule - at least one outlet for the product stream comprising the guidance molecule-linker complexes and/or a reservoir for taking up the guidance molecule-linker complexes (5).
