A composition includes a quantum cluster of Agm or Aun, one or more protector molecules; and a molecular cavity partially or wholly surrounding the quantum cluster. A method for preparing the quantum clusters includes adding a first amount of glutathione to a gold salt, a silver salt, or a mixture thereof to form a mixture; adding a reducing agent to the mixture to form a precipitate; and mixing the precipitate with a second amount of glutathione and a cyclodextrin to form a composition. Devices are prepared from the quantum clusters, and the devices may be used in methods of authentification of articles.