Luminescent, freestanding composite films of Au₁₅ for specific metal ion sensing

Abstract

A highly luminescent freestanding film composed of the quantum cluster, Au₁₅, was prepared. We studied the utility of the material for specific metal ion detection. The sensitivity of the red emission of the cluster in the composite to Cu²⁺ has been used to make a freestanding metal ion sensor, similar to pH paper. The luminescence of the film was stable when exposed to several other metal ions such as Hg²⁺, As³⁺, and As⁵⁺. The composite film exhibited visual sensitivity to Cu²⁺ up to 1 ppm, which is below the permissible limit (1.3 ppm) in drinking water set by the U.S. environmental protection agency (EPA). The specificity of the film for Cu²⁺ sensing may be due to the reduction of Cu²⁺ to Cu¹⁺/Cu⁰ by the glutathione ligand or the Au₁₅ core. Extended stability of the luminescence of the film makes it useful for practical applications.