Two distinct fluorescent quantum clusters of gold starting from metallic nanoparticles by pH-dependent ligand etching

Two fluorescent quantum clusters of gold, namely Au 25 and Au 8 , have been synthesized from mercaptosuccinic acid-protected gold nanoparticles of 4–5 nm core diameter by etching with excess glutathione. While etching at pH ∼3 yielded Au 25 , that at pH 7–8 yielded Au 8 . This is the first report of the synthesis of two quantum clusters starting from a single precursor. This simple method makes it possible to synthesize well-defined clusters in gram quantities. Since these clusters are highly fluorescent and are highly biocompatible due to their low metallic content, they can be used for diagnostic applications.