Uniform arrangement of gold nanoparticles on magnetic core particles with a metal-organic framework shell as a substrate for sensitive and reproducible SERS based assays: Application to the quantitation of Malachite Green and thiram.

Magnetite (Fe3O4) spheres acting as a core were evenly decorated with gold nanoparticles (AuNPs) and coated with a shell of a metal organic framework (MOF) of type MIL-100(Fe). The resulting hybrid nanomaterial of type Fe3O4-Au@MIL-100(Fe) hybrid is shown to be a viable new SERS substrate. The integration of magnetic core, build-in plasmonic gold nanoparticles and a MOF shell endows the Fe3O4-Au@MIL-100(Fe) with highly efficient magnetic separation and enrichment ability, abundant interparticle hotspots, and significant chemical enhancement effect. This leads to a large enhancement, and greatly improved reproducibility of the SERS signals as shown for Malachite Green (MG) and the fungicide thiram. MG in solution can be quantified with a 50-fold lower detection limit (0.14 nM for peak at 1398 cm-1) and largely improved reproducibility (RSD = 9%, 1398 cm-1) when compared to the use of (a) AuNPs anchored on MIL-100(Fe) (RSD = 27%, 1186 cm-1), or (b) AuNPs embedded in MIL-100(Fe) (RSD = 36%, 1398 cm-1). The method was applied to the quantitation of MG and thiram in spiked water samples. The lower limits of detection are 4.4 nM for MG (1398 cm-1) and 15 nM for thiram (1380 cm-1), respectively, and signals' RSDs are 13% (1398 cm-1) and 5% (1380 cm-1) for MG and thiram, respectively. The substrate is recyclable. Graphical abstract Schematic illustration of the preparation and SERS molecule sensing application of Fe3O4-Au@MIL-100(Fe) hybrid. PMMA: poly(methacrylic acid; BPEI: branched poly(ethyleneimine); BTC: 1,3,5-tricarboxybenzene.