The present invention relates to a method for generating at least one polydentate metal chelating affinity ligand, which method comprises the steps of (a) providing at least one scaffold defined by the general formula (I): H2N—(X1)n—S—S—(X2)m—CH2—NH2 wherein X1 and X2 irrespective of each other are carbon atoms or heteroatoms, and n and m irrespective of each other are integers of 1 to 5; (b) providing at least one polydentate metal chelating affinity ligand arm, optionally in a form wherein the metal chelating functionalities of at least one arm are protected, on each scaffold by derivatisation of the nucleophilic NH2 groups of the scaffold; (c) reducing the disulfide bond of the derivatised scaffold; and, if required (d) deprotecting the functionalities of the ligand arm(s) provided in step (b). In the most preferred embodiment, the reduction of the disulfide bond and the deprotection step is performed essentially simultaneously.