Tunable SERS activity of Ag@Fe3O4 core-shell nanoparticles: Effect of shell thickness on the sensing performance

Abstract

Surface enhanced Raman spectroscopy (SERS) with enormous advantages has emerged as a powerful tool for both highly sensitive structural detection of analytes and imaging applications. Among various multifunctional nanomaterials for SERS substrate, nanocomposites of magnetic and plasmonic materials deliver both SERS effect and magnetic manipulation capacity, and thereby, have practical advantages for trace analysis in a broad range of fields. Herein, we investigate the SERS performance of different-sized Ag@Fe3O4 core-shell nanoparticles (NPs) obtained by controlling the Fe precursor concentration in a facile one-pot solvothermal synthesis method. The surface morphology, composition, structure, optical and magnetic properties are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-Vis spectroscopy, and electrochemical techniques. The small shell thickness and high shell porosity of the smallest NPs significantly improve the mass diffusion and therefore SERS performance, making it an ideal substrate for highly sensitive detection of methylene blue (MB) and crystal violet (CV) organic pollutants. Quantitative SERS measurements using the Ag@Fe3O4 NPs are successfully demonstrated with MB as probe analytes. Due to the presence of a porous Fe3O4 shell, the Ag@Fe3O4 NPs showed outstanding SERS sensing performance with a linear concentration range from 10−7 to 10−10 M and the limit of detection (LOD) of 3 × 10−10 M. Moreover, the Ag@Fe3O4 core-shell nanocomposite exhibits high reproducibility and reliability and can be a promising candidate for SERS sensing systems.