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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. [ABSTRACT FROM AUTHOR]

Mercury ion (Hg2+) exposure is a threat to human health. We report a plasmonic core‐satellite Fe3O4@SiO2‐Au (FA) hetero nanostructure for Hg2+ detection using surface enhanced Raman scattering based on the T‐Hg2+‐T strategy. The FA nanostructure was functionalized by a DNA aptamer, which was designed with Cy5 at the 5′ end, and used as a Raman reporter to specifically bind to Hg2+ ions. In the presence of Hg2+, DNA formed a hairpin structure, bringing Cy5 close to the FA hotspots region, thus generating an enhanced Raman signal. The T‐Hg2+‐T complex formed the basis for the determination of trace Hg2+ with a detection limit lower than 5 × 10−9 M, and the influence of other metal ions was found to be negligible. With high selectivity, sensitivity, and recyclability, this FA‐DNA surface enhanced Raman scattering platform is a promising tool for field monitoring of Hg2+ ions. A simple, rapid, and sensitive surface‐enhanced Raman scattering nanosensor for the detection of Hg2+ was developed on the basis of DNA‐functionalized Fe3O4@SiO2‐Au (FA) with a satellite structure. With high selectivity and recyclability, this FA‐DNA surface‐enhanced Raman scattering platform is a promising tool for field monitoring of Hg2+ ions. [ABSTRACT FROM AUTHOR]

Nanomaterials with well-defined structures and optimised electromagnetic hot spots are crucial and highly desirable in surface-enhanced Raman scattering (SERS), but remain challenging to fabricate. In response, theoretical and experimental studies were performed to optimise the parameters of Fe3O4–Au satellite nanostructures for achieving pronounced electric field enhancements. The results indicated that independent control of the size and shape of the satellite nanostructures was insufficient for accurately maximising the SERS effect. A finite-difference time-domain (FDTD) simulation showed that, for ratios of the Au NP size (s) to the nanogap distance between Au NPs (D) ≥20, the magnetic field intensity was the most efficiently enhanced at 785 nm. Using a layer-by-layer fabrication method, satellite structures with the dimensions determined by the FDTD models were generated. The SERS enhancement results from these structures were in agreement with the modelled predictions, emphasising the potential utility of FDTD models in guiding satellite substrate design. For structures with parameters set to the optimised s/D value, the SERS enhancement factor was increased by up to two orders of magnitude. Magnetic satellite platforms optimised via this simulation-based approach possess excellent electromagnetic coupling properties and could assist in the development of new SERS applications. [ABSTRACT FROM AUTHOR]