Polyethylenimine-interlayered silver-shell magnetic-core microspheres as multifunctional SERS substrates

The fabrication of an ideal noble metal modified magnetic microsphere as a high performance SERS substrate that possesses good dispersibility, strong magnetic responsiveness, and high sensitivity is still a challenge. Herein, we report a novel route for fabricating Ag-coated magnetic core-shell microspheres (Fe₃O₄@PEI@Ag) with most of the desired advantages by using polyethyleneimine (PEI) as an interlayer. The size and coverage level of the Ag-NPs shell on Fe₃O₄@PEI@Ag microspheres were easily controlled by varying the amount of AgNO₃. Meanwhile, the magnetic core endowed the Fe₃O₄@PEI@Ag microspheres with superior magnetic nature, which enabled convenient separation and further enhanced Raman signals due to enrichment of targeted analytes and abundant interparticle hotspots created by magnetism-induced aggregation. Considering these features, Fe₃O₄@PEI@Ag is expected to be a versatile SERS substrate, which was verified by the detection of adsorbed PATP molecules and human IgG with a detection limit as low as 10^-11 M and 10^-14 g mL^-1, respectively. Therefore, the novel Fe₃O₄@PEI@Ag microsphere has an enormous potential for practical SERS detection applications, especially in the field of quantitative detection of target proteins.