Mercury Ion-Responsive Coalescence of Silver Nanoparticles on a Silica Nanoparticle Core for Surface-Enhanced Raman Scattering Sensing

Amalgamation of metal nanoparticles (NPs) with mercury (Hg) and the accompanying changes in morphology or localized surface plasmon resonance have received increasing attention in recent years because of their potential applicability in mercury sensing for environmental protection. In this work, the amalgamation of silver NPs (Ag NPs) densely assembled on a silica nanoparticle core is achieved simply by an incubation with aqueous Hg2+. The formation of the Ag-Hg amalgam is followed not only by a coalescence between Ag NPs on silica NP cores but also by a prompt suppression of their surface-enhanced Raman scattering (SERS) activity. Based on the observations, we hypothesize that the suppression of the SERS signal is attributed to the deformation of nanojunctions where the electromagnetic hotspots are located during the coalescence process. In addition, we propose a reducing agent-free method for Hg2+ detection by utilizing the correlation between Hg2+ concentration and the following SERS signal of 4-fluorobenzenethiol introduced as a Raman dye. In the evaluation of analytical performance, the proposed method exhibits rapidness within 1 min and improved signal reproducibility with relative standard deviations below 4.62% compared to the conventional SERS methods for Hg2+ detection.