Plasmonic Nanocubes\nwith a Controllable “Crescent\nArc” Facet: Tunable Hotspot Engineering for Highly Reliable\nand Sensitive SERS Detection

The fine control of the nanogap and morphology of metal\nnanoparticles\n(NPs) has always been an obstacle, hindering the development and application\nof surface-enhanced Raman scattering (SERS) quantitative detection.\nHere, Au/4-mercaptobenzoic acid@Ag@Au–Ag bimetal core–shell\nnanocubes (NCs) with a “crescent arc” facet (C-Au/4MBA@Ag\nNCs) as a highly reliable and sensitive surface-enhanced Raman scattering\nSERS substrate is proposed for the first time. The bifunctional internal\nstandard (IS) molecules (4MBA) govern the morphology of metal shells\nto maintain cubic configuration and provide calibration for SERS signals’\nflotation. In parallel, the controllable curvature of the C-Au/4MBA@Ag\nNCs is directly modulated by adjusting the relative rates of the galvanic\nreplacement and co-reduction reaction, which generates a controllable\ninterparticle nanogap to offer large depositing spaces for analytes\nand improve authoritative SERS signals’ enhancement. The proposed\nC-Au/4MBA@Ag NCs exhibit an enhancement factor of up to 4.8 ×\n10<sup>10</sup> and contribute to the ultralow RSD (7.9%). These C-Au/4MBA@Ag\nNCs also enable the detection of hazardous pesticide residues such\nas methamidophos and thiram in herbal plants with a complex matrix,\nwith an average detection accuracy of up to 96%. In summary, this\nstudy achieves a fine control strategy of the “crescent arc”\nsurface for improving SERS performance and explores the practical\napplication potential for accurate and sensitive Raman detection of\nhazardous substances.