Two Distinct Fluorescent Quantum Clusters of Gold Starting from Metallic Nanoparticles by pH-Dependent Ligand Etching

Two fl uorescent quantum clusters of gold,namely Au25 and Au8,have been synthesized from mercaptosuccinic acid-protected gold nanoparticles of 45 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 fi rst 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 fl uorescent and are highly biocompatible due to their low metallic content,they can be used for diagnostic applications.