SERS hotspot engineering using external field assembly of a plasmonic magnetic nanocomposite with high sensitivity and uniformity

Abstract

Surface-enhanced Raman scattering (SERS) is a pivotal analytical technique in sensing, yet it grapples with challenges such as reproducibility, substrate stability, and hotspot uniformity. The use of highly effective external field nanocomposites facilitates the dynamic manipulation of “hotspots”—the nanoscale gaps between metal nanoparticles—which is critical for SERS enhancement. The gap between 4-mercaptopyridine-modified (4-MPY) Fe₃O₄@SiO₂@Au nanocomposites (FA) can be precisely reduced by applying an external magnetic field, resulting in up to a 30-fold increase in SERS signal intensity and an 8–39 times increase in the enhancement factor (EF). This approach markedly enhances SERS signal uniformity, demonstrated by the relative standard deviation of the EF dropping from 59.15–9.44% to 28.70–1.14%. By systematically studying the correlations between the SERS EF and the external-magnetic-field strength, hotspot density, and probe molecular density, sensitive magnetic, SERS platforms are established. The optimal hotspots occur in the magnetic field of 80 to 120 mT among the FA-4MPY nanocomposites, as validated by COMSOL finite-element analysis simulations. These findings offer a nuanced understanding of magnetic SERS hotspot tuning, paving the way for precise and improved molecular sensing.