Recyclable Fe3O4@SiO2@PEI-DTC@Au-Ag nanocomposites as a SERS platform for sensitive detection of thiram on fruit surfaces

Equipped with surface-enhanced Raman scattering (SERS) effect and magnetic manipulation capacity, a new paradigm of recyclable SERS substrates based on Fe 3 O 4 nanoparticles (NPs) @SiO 2 @PEI-DTC adhesive layer @Au-Ag alloy quantum dots (QDs) were successfully prepared via engineering hydrothermal and seed deposition techniques. The SERS performance and uniformity of those substrates with different gold-silver (Au-Ag) weight ratios were evaluated by 4-aminothiophenol (4-ATP) molecules, revealing that the relative standard deviations (RSDs) of all substrates were less than 12 %, with the optimal SERS substrate achieving an enhancement factor (EF) of up to 1.39 × 10 5 . This phenomenon can be attributed to the magnetic core and plasmonic resonance properties of Au-Ag alloy QDs, which result in abundant interparticle hotspots in the Fe 3 O 4 @SiO 2 @PEI-DTC@Au-Ag (FSPAA) nanocomposites. Furthermore, the optimal FSPAA nanocomposite was employed as a SERS substrate for rapid non-destructive detection of thiram on fruit surfaces. The SERS signal intensity exhibited a robust manifesting a linear association with thiram concentration within the span of 1 × 10 −4 to 1 × 10 −9  M, and the minimal detectable concentration was 1.04 × 10 −10  M. The FSPAA core–shell nanocomposites exhibit high reusability and reliability and hold great promise for the practical applications in on-site assessment of food/environmental safety, as well as in spectroscopic identification of molecules adsorbed onto fruit surfaces.