The fourth-power dependence on wavelength was used to adjust for the differences between excitation wavelengths. Additionally, we assumed that SERS intensity is proportional to both laser power and acquisition time. To accurately estimate Nbulk, we determined the effective focus volume for SM-SERS EF calculations. Briefly, the laser beam was approximated as a Gaussian beam, and the knife-edge method was employed to measure the beam waist (w0). A slit width of 250 μm was used, representing the minimal width at which further expansion no longer increased signal intensity. The effective volume was calculated using the relationship Veff = Aeff × Heff, where Aeff = P0/I0 = πw0 2 /2 for a Gaussian beam. Extended Data Fig. illustrates the bulk Raman spectrum and the evaluation procedure for the effective volume. We obtained the values Aeff = 0.328 μm 2 , Heff = 0.986 μm, and Veff = 0.323 μm 3 . On average, each nano-Fanowman particle contained ~356 Cy5 dye molecules (NSERS = 356), determined by fluorescence measurements . The single-particle SERS intensity (ISERS) was measured using a slit size of 100 μm. To correct for intensity discrepancies arising from the different slit widths between bulk and SERS measurements, we determined a correction factor of 3.136 by measuring the silicon peak intensity at each slit width. Subsequently, Ibulk was divided by this factor. ) of the Cy5 dye, respectively. As the number of nanobridges increases, a pronounced Fano dip forms and gradually blueshifts, and the strongest hot spot appears at wider junction widths, also accompanied by a blueshift while the maximum |E/E0| 2 intensity at these hot spots gradually decreases. Thus, identifying an optimal structure that simultaneously maximises SERS enhancement at both the laser excitation and Raman Stokes wavelengths is critical for achieving superior SERS performance.