Fabrication and magnetic-induced aggregation of Fe₃O₄ –noble metal composites for superior SERS performances

Fe₃O₄–noble metal composites were obtained by combining Au, Ag nanoparticles (NPs) with 3-aminopropyltrimethoxysilane-functionalized Fe₃O₄ NPs. UV–Visible absorption spectroscopy demonstrates the obtained Fe₃O₄ –noble metal composites inherit the typical surface plasmon resonance bands of Au, Ag at 533 and 453 nm, respectively. Magnetic measurements also indicated that the superparamagnetic Fe₃O₄ –noble metal composites have excellent magnetic response behavior. A magnetic-induced idea was introduced to change their aggregated states and take full advantage of their surface-enhanced Raman scattering (SERS) performances. Under the induction of an external magnetic field, the bifunctional Fe₃O₄ –noble metal aggregates exhibit the unique superiority in SERS detection of Rhodamine 6G (R6G), compared with the naturally dispersed Au, Ag NPs. Especially, the detection limit of the Fe₃O₄–Ag aggregates for R6G is as low as 10⁻¹⁴ M, and the calculated EF reaches up to 1.2 × 10⁶, which meets the requirements for trace detection of analytes. Furthermore, the superiority could be extended to sensitive detection of other organic molecules, such as 4-mercaptopyridine. This work provides a new insight for active adjustment of the aggregated states of SERS substrates and the optimization of SERS performances.