Reusable nanosilver-coated magnetic particles for ultrasensitive SERS-based detection of malachite green in water samples

A novel nanosilver-deposited silica-coated Fe₃O₄ magnetic particle (Fe₃O₄@SiO₂@Ag) with uniform size, good SERS activity and magnetic responsiveness was synthesized using amination polymer. The Fe₃O₄@SiO₂@Ag magnetic particles have been successfully applied for ultrasensitive SERS detection of malachite green (MG) in water samples. The mechanism is that MG can be adsorbed on the silver surface of nanosilver-coated magnetic particles via one nitrogen atom, and the Raman signal intensity of MG is significantly enhanced by the nanosilver layer formed on the magnetic particles. The developed sensing system exhibited a sensitive response to MG in the range of 10 fM to 100 μM with a low limit of detection (LOD) 2 fM under optimal conditions. The LOD was several orders of magnitude lower than those of other methods. This SERS-based sensor showed good reproducibility and stability for MG detection. The silver-coated magnetic particles could easily be regenerated as SERS substrates only using low pH solution for multiple sensing events. The recovery of MG added to several water samples at different concentrations ranged from 90% to 110%. The proposed method facilitates the ultrasensitive analysis of dyes to satisfy the high demand for ensuring the safety of water sources.