A hotspot-engineered quasi-3D metallic network with controllable nanogaps is purposed as a high-quality surface-enhanced Raman scattering (SERS) substrate, which is prepared by a combination of non-close-packed colloid monolayer templating and metal physical deposition. The significant SERS effect arises from a strongly enhanced local electric field originating from the ultra-small-gaps between neighboring metal-caps and tiny interstices and between the metal-caps and the metal-bumps on the base, which is recognized by the numerical simulation. A remarkable average SERS enhancement factor of up to 1.5 × 108 and a SERS intensity relative standard deviation (RSD) of 10.5% are achieved by optimizing the nanogap size to sub-10 nm scale, leading to an excellent capability for Raman detection, which is represented by the clearly identified SERS signal of the Rhodamine 6G solution with a fairly low concentration of 1 nM.

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