Fe₃O₄@SiO₂–SO₃H@PPy@Au spheres: Fabrication, characterization and application in SERS

In this work, the sulfonic acid (–SO₃H) group terminated Fe₃O₄@SiO₂ magnetic spheres were prepared. Polypyrrole (PPy) was in-situ polymerized on Fe₃O₄@SiO₂–SO₃H spheres due to the dual roles of the –SO₃H groups: acting as both "anchoring sites" for adsorbing of pyrrole monomer and dopant agent in PPy. By adsorbing gold nanoseeds on the as-prepared Fe₃O₄@SiO₂–SO₃H@PPy spheres followed the seed-mediated growth method, the multifunctional Fe₃O₄@SiO₂–SO₃H@PPy@Au spheres were obtained. The application of Fe₃O₄@SiO₂–SO₃H@PPy@Au spheres in surface-enhanced Raman scattering (SERS) was investigated, and the results exhibited the enhancement in the order of 10⁴ using 4-aminothiophenol as the probe molecule. - Highlights: • The sulfonic acid-terminated Fe₃O₄@SiO₂ (Fe₃O₄@SiO₂–SO₃H) spheres were prepared. • The –SO₃H groups of Fe₃O₄@SiO₂–SO₃H spheres played dual roles in adsorbing pyrrole and protonating polypyrrole. • Fe₃O₄@SiO₂–SO₃H@PPy core/gold shell composites can act as SERS substrate for detecting 4-ATP molecule.