In general however linkers will be from 100 to 100 000 D, especially 120 D to 20 kD in molecular weight. [0192] Conjugation of linker to vector and linker to reporter may be by any appropriate chemical conjugation technique, eq. covalent bonding (for example ester or amide formation), metal chelation or other metal coordinative or ionic bonding, again as described above. [0193] Examples of suitabl