Cube-like Fe₃O₄@SiO₂@Au@Ag magnetic nanoparticles: a highly efficient SERS substrate for pesticide detection

As a novel surface-enhanced Raman spectroscopic (SERS) nanocomposite, cube-like Fe₃O₄@SiO₂@Au@Ag magnetic nanoparticles (NPs) were synthesized for the first time. Cube-likeα-Fe₂O₃NPs with uniform size were achieved by optimizing reaction temperature and time. Firstly, the cube-like Fe₃O₄@SiO₂with good dispersity was achieved by calciningα-Fe₂O₃@SiO₂NPs in hydrogen atmosphere at 360 °C for 2.5 h, followed by self-assembling a PEI shell via sonication. Furthermore, the Au@Ag particles were densely assembled on the Fe₃O₄@SiO₂NPs to form the Fe₃O₄@SiO₂@Au@Ag composite structure via strong Ag-N interaction. The obtained nanocomposites exhibited an excellent SERS behavior, reflected by the low detection of limit (p-ATP) at the 5 × 10^-14M level. Moreover, these nanocubes were used for the detection of thiram, and the detection limit can reach 5 × 10^-11M. Meanwhile, the U.S. Environmental Protection Agency specifies that the residue in fruit must be lower than 7 ppm. Hence, the resulting substrate with high SERS activity has great practical potential applications in the rapid detection of chemical, biological, and environment pollutants with a simple portable Raman instrument at trace level.