Satellite Fe3O4@SiO2–Au SERS probe for trace Hg2+ detection

Abstract

Plasmonic core–satellite Fe₃O₄@SiO₂–Au (FA) was synthesized for Hg²⁺ detection based on the “turn-off” SERS strategy. The functionalization of FA simply included the adsorption of congo red (CR) to FA through a PDDA linker. In the presence of Hg²⁺, CR molecules are released from the substrate, thus generating a decreased peak intensity in the observed Raman spectra. This “turn-off” effect serves as the basis for the determination of trace Hg(II) with a detection limit of 1 × 10⁻⁸ M. The strong interaction between Hg²⁺ and the SERS substrate was confirmed by zeta potential and SEM-EDS analysis. The XANES results show that 94% of Hg on the substrate was reduced to Hg⁰, indicative of an Hg–Au amalgam formation. The interference from other metal ions and humic acids commonly encountered in the environment was negligible. This FA–CR SERS platform is a promising tool for monitoring mercury ions in environmental applications.