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

As a novel SERS nanocomposities, cube-like Fe3O4@SiO2@Au@Ag magnetic nanoparticles have been synthesized for the first time. Cube-like α-Fe2O3 NPs with uniform size can be achieved by optimizing reaction temperature and time. Firstly, the cube-like Fe3O4@SiO2 with good dispersity were achieved by calcining α-Fe2O3@SiO2 NPs in hydrogen atmosphere at 360 °C for 2.5 h, followed by self-assembling PEI shell via sonication. Furthermore, the Au@Ag particles can be densely assembled on the Fe3O4@SiO2 NPs to form the Fe3O4@SiO2@Au@Ag composite structure via strong Ag-N interaction. The obtained nanocomposites exhibit an excellent surface-enhanced Raman (SERS) behavior, reflected from low detection of limit (p-ATP) at 5×10-14 M level. Moreover, these nanocubes are used for detection of thiram and the detection limit can reach up to 5×10-11 M, while the rule of 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 rapid detection of chemical, biological and environment pollutants with a simple portable Raman instrument at trace level.