Penicillamine-protected Ag20 nanoclusters and fluorescence chemosensing for trace detection of copper ions.

We report the synthesis of penicillamine-protected Ag20 nanoclusters (NCs), with properties of high monodispersity, red fluorescence and water solubility. Full characterization of the Ag20 NCs is addressed, along with first-principles optimization calculations, revealing the chemical composition and structure of the as-prepared Ag NCs within a molecular formula [Ag20(DPA)18-H]-. Moreover, natural bond orbital (NBO) analysis demonstrates the charge-transfer interactions between the ligand and Ag atoms, and helps in understanding the origins of fluorescence of Ag20 NCs related to the ligand-to-metal charge transfer (LMCT) mechanism. Further, fluorescence chemosensing of the Ag20 NCs is demonstrated for tracing copper ions with high sensitivity and selectivity in aqueous solution.