Auto-Decomposition of Ag+-Citrate Complex Leads to the Formation of Uniform Ag Shell on Citrate-Capped Gold Nanoparticles

Abstract

Bimetallic core-shell nanoparticles have emerged as a more economical and versatile platform that find applications in a wide range of fields such as biosensing, catalyst, and biomedicine. However, their synthesis by the popular seed-mediated growth method suffers from contamination by secondary seeds from heterogeneous nucleation and, thus, often requires combinational use of stabilizing agents and stringent kinetic control. Here, we report a seed-induced growth method for the synthesis of exclusively Au-Ag core-shell nanoparticles, where Ag+-citrate complex adsorbed on the surface of AuNP seeds automatically decomposed to form an ultrathin Ag shell. By studying the complexation process by DLS and zeta potential, the shell formation kinetics by UV-vis, and the nanoparticle structure by TEM and EDS, we identified that the Ag shell had a maximum thickness of around 3 nm, which was limited by the amount of adsorbed Ag+-citrate complex. Nonetheless, the obtained core-shell nanoparticles were highly uniform and free from secondary silver nanoparticle byproducts. Thus, this finding not only provides a simple and efficient avenue to but also offers novel insights for the synthesis of core-shell bimetallic nanoparticles.

Keywords: Au-Ag core-shell nanoparticles, Ag+-citrate complex, auto-decomposition, seed-mediated growth