Fluorescent Au@Ag Core–Shell Nanoparticles with Controlled Shell Thickness and HgII Sensing

Au–Ag core–shell nanoparticles have been synthesized using synthetic fluorescent dipeptide β-Ala-Trp (β-Ala is β-alanine; Trp is l-tryptophan) in water at pH 6.94 and at room temperature. The synthesis of the Au–Ag core–shell nanomaterial does not involve any external reducing and stabilizing agents, and the constituents of dipeptide β-alanine and l-tryptophan are naturally occurring. Therefore, the synthesis procedure is ecofriendly. Moreover, the shell thickness has also been controlled, and the optical property of the core–shell nanomaterial varies with the shell thickness. The core–shell nanomaterial exhibits a fascinating fluorescence property. This fluorescent Au@Ag core–shell nanoparticle can detect toxic HgII ions ultrasensitively (with a lower limit of detection of 9 nM) even in presence of ZnII, CdII, and other bivalent metal ions (CaII, MgII, NiII, MnII, BaII, SrII, PbII, and FeII). Au–Ag core–shell nanomaterials can also be reused for sensing HgII ions.