LAUSR

Metal nanostructures with a tunable plasmonic gap are useful for photonics, surface‐enhanced spectroscopy, biosensing, and bioimaging applications. The use of these structures as chemical and biological sensing/imaging probes typically requires an ultra‐precise synthesis of the targeted nanostructure in a high yield, with Raman dye‐labeling and complex assay components and procedures. Here, a plasmonic nanostructure with tunable dual nanogaps, Au dual‐gap nanodumbbells (AuDGNs), is designed and synthesized via the anisotropic adsorption of polyethyleneimine on Au nanorods to facilitate tip‐selective Au growths on nanorod tips for forming mushroom‐shaped dumbbell‐head structures at both tips and results in dual gaps (intra‐head and inter‐head gaps) within a single particle. AuDGNs are synthesized in a high yield (>90%) while controlling the inter‐head gap size, and the average surface‐enhanced Raman scattering (SERS) enhancement factor (EF) value is 7.5 × 108 with a very narrow EF distribution from 1.5 × 108 to 1.5 × 109 for >90% of analyzed particles. Importantly, AuDGNs enable label‐free on‐particle SERS detection assays through the diffusion of target molecules into the intraparticle gap for different DNA sequences with varying ATGC combinations in a highly specific and sensitive manner without a need for Raman dyes.