Controlled Formation of Emissive Silver Nanoclusters Using Rationally Designed Metal-Binding Proteins

The metal-binding properties of rationally designed, synthetic proteins were used to prepare a series of emissive silver nanoclusters having predictable sizes and emission energies. Metal-binding α-helical coiled coils were designed to exist as peptide trimers, tetramers, and hexamers and found to uniquely bind 6, 8, and 12 Ag⁺ ions, respectively. Subsequent treatment with a chemical reducing agent produced a series of peptide-bound Ag⁰ nanoclusters that display a strong visible fluorescence whose emission energies depend on the number of bound metal ions in excellent agreement with theory.