Top-down synthesis of the clusters can be achieved by the "etching"  of larger metallic nanoparticles with redox-active, thiol-containing biomolecules. In this process, gold atoms on the nanoparticles' surface react with the thiol, dissolving as gold-thiolate complexes until the dissolution reaction stops; this leaves behind a residual species of thiolate-protected gold clusters that is particularly stable. This type of synthesis is also possible using other non thiol-based ligands.