Fluorescent Au@Ag core-shell nanoparticles with controlled shell thickness and Hg(II) 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 Hg(II) ions ultrasensitively (with a lower limit of detection of 9 nM) even in presence of Zn(II), Cd(II), and other bivalent metal ions (Ca(II), Mg(II), Ni(II), Mn(II), Ba(II), Sr(II), Pb(II), and Fe(II)). Au-Ag core-shell nanomaterials can also be reused for sensing Hg(II) ions.