Fluorescent Ag clusters via a protein-directed approach as a Hg(II) ion sensor

Proteins have proven to be particularly attractive as effective ligands in the synthesis of nano- and subnanoscaled materials because of their multiple chelating and functional groups imparting unique functionalities. However, protein-directed fluorescent metal cluster synthesis is still a challenge but a promising area of research. Here, we report on the synthesis of new water-soluble, stable, fluorescent Ag clusters via a facile, green method using denatured bovine serum albumin (dBSA) as a stabilizing agent. The dBSA with its 35 free cysteine residues could contribute to polyvalent interactions with the Ag clusters and serve as effective stabilizing agents for these clusters. The as-prepared Ag clusters showed high fluorescence emission at ∼637 nm and were stable even in 1 M NaCl. The fluorescent Ag clusters were then used in the detection of Hg(2+) with high sensitivity and selectivity. The detection limit was 10 nM in the linear range from 10 nM to 5 μM.